A&A 454, 759-772 (2006)
DOI: 10.1051/0004-6361:20064883
The structure of galactic disks
Studying late-type spiral galaxies using SDSS![[*]](/icons/foot_motif.gif)
M. Pohlen1,2 - I. Trujillo3,4
1 -
Kapteyn Astronomical Institute, University of Groningen, PO Box 800,
9700 AV Groningen, The Netherlands
2 -
Instituto de Astrofísica de Canarias, C/ Via Láctea s/n,
38200 La Laguna, Tenerife, Spain
3 -
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117
Heidelberg, Germany
4 -
School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
Received 20 January 2006 / Accepted 26 April 2006
Abstract
Using imaging data from the SDSS survey, we present the
and
radial stellar light distribution of a complete sample of
90 face-on to intermediate inclined, nearby, late-type (Sb-Sdm)
spiral galaxies. The surface brightness profiles are reliable (
uncertainty less than 0.2 mag) down to
mag/
. Only
10% of all galaxies have a normal/standard purely exponential
disk down to our noise limit.
The surface brightness distribution of the rest of the galaxies is better
described as a broken exponential. About 60% of the galaxies have a break in
the exponential profile between
1.5-4.5 times the scalelength
followed by a downbending, steeper outer region. Another
30%
shows also a clear
break between
4.0-6.0 times the scalelength but followed by an
upbending, shallower outer region. A few galaxies have even a more
complex surface brightness distribution.
The shape of the profiles correlates with Hubble type. Downbending breaks
are more frequent in later Hubble types while the fraction of upbending
breaks rises towards earlier types. No clear relation is found between the
environment, as characterised by the number of neighbours, and the shape of
the profiles of the galaxies.
Key words:
galaxies: photometry -
galaxies: structure -
galaxies: fundamental parameters -
galaxies: evolution -
galaxies: formation
1 Introduction
The structural properties of the faintest regions of galactic disks
must be intimately linked to the mechanisms involved in the growing and
shaping of galaxies. These outer edges are easily affected by
interactions with other galaxies and, consequently, their characteristics
must be closely connected with the evolutionary path followed by the
galaxies. Together with their stellar halos, the study of the outer edges
allows the exploration of the so-called fossil evidence imprinted by the
galaxy formation process.
Most of the so far detailed structural studies of nearby disk galaxies
(MacArthur et al. 2003; Jansen & Kannappan 2001; Möllenhoff 2004; Courteau 1996; Trujillo et al. 2002; de Jong 1996; Graham 2001) have been concentrated on the (most
easily accessible) inner parts of the galaxies.
These studies of the brightest region of the stellar disk show that its
light distribution is almost always well described by a simple exponential
decline going back to Patterson (1940), de Vaucouleurs (1959),
or Freeman (1970).
This simple description, however, has now been shown to fail at fainter
surface brightness. In fact, since van der Kruit (1979) we know that this decline
does not continue to the last measured point, but is truncated after
several radial scalelengths.
The main concern with current, larger statistical studies exploring the
faintest surface brightness region of the galaxies is that they are based
on edge-on galaxies
(de Grijs et al. 2001; Kregel et al. 2002; Pohlen 2001; Barteldrees & Dettmar 1994; Florido et al. 2001; Pohlen et al. 2000a).
This geometry facilitates the
discovery of the truncation in the surface brightness profiles, but
introduces severe problems caused by the effects of dust and the
line-of-sight integration (Pohlen et al. 2004, for a recent review),
such as masking the actual shape of the truncation region, or interfering
with the identification of other important disk features (e.g. bars, rings,
or spirals).
Only few works have probed the faintest regions of the disk galaxies in low
inclination systems. Pohlen et al. (2002) demonstrated for a small sample of
face-on galaxies that the so-called cut-offs in the surface brightness
profiles discovered by van der Kruit are in fact not complete but better
described by a broken exponential with a shallow inner and a steeper outer
exponential region separated at a relatively well defined break radius.
However, not all the galaxies seem to have a break or a truncation in their
surface brightness profiles. Just recently Bland-Hawthorn et al. (2005) found
(using star counts) again a galaxy (NGC 300) for which the exponential
decline simply continues down to
10 radial scalelength. Together with
earlier measurements by Barton & Thompson (1997) or Weiner et al. (2001) (using
surface photometry) this provides evidence that indeed there are
prototypical, model exponential disks.
Our picture of the faintest regions of spiral galaxies have been even
broadened with some recent studies. Erwin et al. (2005a), studying a large sample
of early-type barred S0-Sb galaxies, discovered that there is more than
truncated or untruncated galaxies. They report the detection
of antitruncated galaxies, which show also a broken exponential
but having the opposite behaviour, an outer upbending profile. Similar
structures are also found for a large sample of irregular systems (Im)
and BCDs by Hunter & Elmegreen (2006).
The disk structures we describe in this study are the result of
initial conditions, infalling matter and/or redistribution of gas
and stars, already settled in the disk, triggered
by internal (e.g. bars) or external (e.g. interaction) forces.
All these processes are linked to the detailed mechanism of forming
the stars which build up the observed brightness distribution.
To explain for example the observed truncation in the surface
brightness profiles radial star-formation thresholds
(e.g. Kennicutt 1989; Schaye 2004) have been suggested
(see Pohlen et al. 2004).
However, there is compelling evidence of star-formation in the
far outer regions of spiral galaxies
(e.g. Thilker et al. 2005; Ferguson et al. 1998; Gil de Paz et al. 2005; Cuillandre et al. 2001),
well beyond the break of the observed broken exponential
structure (Pohlen et al. 2002).
The outer star formation activity argues against a simple
threshold scenario.
Just recently, though, Elmegreen & Hunter (2006) show that their model
of star-formation is able to produce the variety of observed
radial profiles. Alternatively, Debattista et al. (2006) also find
downbending breaks using purely collisionless N-body
simulations.
The main goal of the present study is to conduct a complete census of the
outer disk structure of late-type galaxies - together with a complementary
study by Erwin et al. (2006) for early-type (barred) galaxies - in the local
universe.
The objective is to provide the frequencies of the different surface
brightness profile types, the structural disk parameters, and search
for correlations (if any) between them.
Aside from the observations showing the increasing complexity of
radial surface brightness profiles, the breaks in the surface
brightness distribution can be used to directly constrain galaxy
evolution. Pérez (2004) showed
that it is possible to detect stellar truncations even out to higher
redshift (
). So using the radial position of the truncation as
a direct estimator of the size of the stellar disk, Trujillo & Pohlen (2005)
infer a moderate (
25%) inside-out growth of the disk galaxies
since
,
using as a local reference the galaxies studied
in this paper.
The remainder of this paper is organised as follows. In Sect. 2
we describe the sample selection and our environment parameter. In
Sect. 3 we give the details about the ellipse fitting and the
SDSS imaging used, characterising their quality and addressing
the crucial issue of sky subtraction. The applied classification schema
of the observed profiles and the derived parameters are discussed in
Sect. 4. The results are presented in Sect. 5
and briefly discussed in Sect. 6.
The colour profiles and the physical implications derived from
them will be discussed in a subsequent paper.
In Appendices A we give detailed comments for all galaxies,
show their
and
-band surface brightness
profiles and reproduce their SDSS colour pictures.
2 The sample
2.1 Selection
We selected our initial galaxy sample from the
LEDA
online galaxy
catalogue (version Nov. 2004), since this is the richest catalogue with
homogeneous parameters of galaxies for the largest available sample.
We restricted the Hubble type (T parameter), the mean heliocentric
radial velocity relative to the Local Group
(corrected for virgocentric inflow,
), the axis ratio
(major axis/minor axis), the absolute B-magnitude (
),
and the Galactic latitude (
).
The Hubble type is chosen to be between
2.99 < T < 8.49
(corresponding to Sb to Sdm galaxies) building an
intermediate- to late-type galaxy sample.
This allows a complementary study to the work by Erwin et al. (2006) on
the disk structure of early type (barred) galaxies. To have some,
but not too much, overlap with their sample we did not include all
Sb galaxies by excluding the range
2.49<T<2.99.
The axis ratio is selected to be
(equal to a/b<2
or e<0.5, which corresponds to an inclination of
assuming an intrinsic flattening of q0=0.14) bringing a face-on to
intermediate inclined galaxy sample.
This is necessary to avoid the influence of the dust and is convenient
to provide reliable information on the morphological features such as
bars, rings, or spiral arm structure.
The recession velocity is chosen to be
km s-1 and the galaxies
brighter than -18.4
in B band (the total B-magnitude,
provided by LEDA, is corrected for galactic and internal extinction, k
corrected, and the distance modulus is derived from the recession velocity
corrected for Virgo infall with a Hubble constant of
km s-1 Mpc-1).
We did not apply a diameter limit.
Since SDSS, our data source, is a survey of the high Galactic latitude
sky, visible from the northern hemisphere, there is no worry about
incompleteness there. In any case, we restricted the initial sample to
.
To assess the completeness of the LEDA catalogue Baryshev & Paturel (2001) draw
several cumulative curves
versus
(N is the total
number of observed galaxies within the radius r in Mpc) for
different absolute magnitudes and compare these with an expected
galaxy distribution.
Using the same approach we have confirmed that LEDA
(version Nov. 2004) is almost complete for galaxies of
within our
46 Mpc survey distance (estimated
following the Hubble relation with
km s-1 Mpc-1).
Our selection criteria result in a total number of
655 galaxies, of which 98 (15%) are part of the SDSS Second
Data Release (DR2), surveying the north Galactic cap and three
stripes in the southern Galactic cap (Abazajian et al. 2004; York et al. 2000).
The global parameters
for this subsample of
98 galaxies are presented in Table 1.
Histograms showing the distribution of Hubble type and absolute
magnitude (cf. Fig. 1) reveal that the subsample
restricted by the SDSS DR2 coverage is apparently unbiased in this
sense. There is a lack of very bright galaxies
(
B-mag) due to the small number statistics.
Plotting absolute magnitude
with Hubble Type T reveals
- although with a lot of scatter - a mild trend of earlier Hubble
type galaxies being on average brighter.
Only three galaxies (NGC 4273, NGC 4480, NGC 4496A) are possible
members of the Virgo Cluster according to their VCC numbers
by Binggeli et al. (1985).
![\begin{figure}
\par\includegraphics[width=5.6cm,angle=270]{4883f001.ps}\hspace*{3mm}
\includegraphics[width=5.6cm,angle=270]{4883f002.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg124.gif) |
Figure 1:
Histogram showing the distribution of galaxies covering
the morphological types (T) and absolute magnitude (
) for the
full LEDA sample (rising hashed lines) and the studied SDSS DR2
subsample (falling hashed lines). |
Open with DEXTER |
In this sense our sample is a faithful representation of
the local spiral galaxy population providing a volume limited
sample (
Mpc) of late-type, intermediate inclined to
face-on nearby
galaxies brighter than -18.4 B-mag.
The Appendices A and B show colour images
for all galaxies.
2.2 Environment
To characterise the environment we counted neighbours around our
sample galaxies using the SDSS database from a more recent
Data Release (DR3, Abazajian et al. 2005).
According to the distance, derived from the infall corrected velocity,
we sum all the DR3 galaxies within a projected radius of 1 Mpc that
satisfy the following criteria: the difference in velocity with respect
to the targeted galaxy is less than 350 km s-1 (Giuricin et al. 2000)
and their absolute magnitude is brighter than
-mag.
It is important to note, however, that the density of galaxies could
be affected by the position of the galaxy within the survey.
If the targeted galaxy is close to the edge of the survey or to a
region where the redshift completeness (fraction of photometrically
detected galaxies with redshifts) is not high, the number of
neighbours could be underestimated.
To eliminate such a problem we have estimated whether the distance
of our galaxy to the edge of the survey or to a redshift incomplete
region is less than 1 Mpc.
If this is the case this galaxy is not used in the analysis
of the effect of the density on the galaxy profile type.
3 Data and profile extraction
3.1 The data
The Sloan Digital Sky Survey (SDSS) (York et al. 2000)
will map one-quarter (
)
of the entire sky mainly
around the north galactic cap (above Galactic latitude
)
in five bands,
,
,
,
and
(Smith et al. 2002; Fukugita et al. 1996). SDSS imaging are obtained
using a drift-scanning mosaic CCD camera (Gunn et al. 1998) with a pixel
size of
.
We downloaded the
and
band images (which have a median PSF
of
1.4
in
)
of the night sky ("corrected frames")
in fits format using the Data Archive Server
.
The
,
and
bands
images are less sensitive
and, consequently, less useful to study the profile towards the outer disk.
The corrected frames, having been bias subtracted, flat-fielded,
and purged of bright stars are stored at SDSS in integer format
to save disk space. According to the
SDSS helpdesk the pixel values get randomised appropriately before
being rounded to make sure that the statistics of the background
counts are what they should be.
An additional offset (SOFTBIAS) of 1000 counts is added to each
pixel to avoid negative pixel values and should be subtracted together
with the sky value (as described in Sect. 3.3).
After inspecting all images for the 98 galaxies we had to remove
13 galaxies (marked with a
in Table 1) from
further analysis (cf. Appendix B).
For four galaxies (NGC 0988, NGC 4900, UGC 04684, and UGC 06162)
there are one (or more) very bright foreground stars too close to the
galaxy preventing any useful surface brightness measurement.
Another six galaxies (NGC 0428, NGC 2712, NGC 4116, NGC 4496A,
NGC 5364, and UGC 09215) are very close to the border of the SDSS
field (more than 1/3 of the galaxy is off the image). To avoid any
problems while trying to recover the galaxies with a mosaic out of
two or even three images we discarded them.
Two peculiar galaxies (NGC 3023 and NGC 5218) are removed since
they are clearly interacting systems. They are gravitationally
highly distorted and in the case of NGC 5218 connected by an intergalactic
bridge to its companion.
One galaxy (PGC 032356
UGCA 219) turns out to be a BCD
galaxy and probably even a double system.
This leave 85 galaxies for the final analysis.
3.2 Photometric calibration
The photometric calibration is done using the aa, kk, and airmass
coefficients (the photometric zeropoint, the extinction term
and the airmass) out of the associated TsField table file for
each image.
From this we calculated
our surface brightness zeropoints as:
using the pixel scale of
/pixel and the exposure
time of 53.907456 s for each SDSS pixel.
Our magnitudes are the conventional Pogson astronomical
magnitudes in the SDSS
and
AB system in contrast to
the asinh magnitudes used in the SDSS database.
The applied zero points are given in Table 2.
To transform the SDSS
and
standard-star system
magnitudes
into the commonly used Johnson-Cousins B, R system, we applied
the transformation equations given in Smith et al. (2002):
and
.
For eight galaxies of the final SDSS sample we found aperture
measurements in the literature. Synthetic aperture measurements
on the SDSS images agree with these previous published values in
the majority of cases to better than 0.1 mag.
All profiles and surface brightness results, given in Table
3, are the measured values from the uncorrected SDSS
data. Only at calculating mean values and plotting histograms we
applied the galactic extinction correction according to
Schlegel et al. (1998) using
.
The values we used for
and
are also shown
in Table 3.
No attempt was made to correct the surface brightness measurements for
internal extinction, since no unique recipe is available to do this.
In addition, the galaxies studied here are all fairly face-on
systems (
)
so the expected
corrections are only small. Since we are working with a local
sample (
)
we also do not correct for the cosmological surface
brightness dimming.
3.3 Sky subtraction
The crucial point in using SDSS data (and in general) to study surface
brightness profiles at very faint levels is the measurement of an
appropriate sky value. SDSS provides in the header of each image a
first estimate of such a value. However, this is just a global value
which is in more than half of the cases off by more than
0.2 counts
(
0.2% level) and therefore for our purposes not accurate
enough.
We need a more elaborated value depending on the size of the
galaxy, thus the area of sky covered by the galaxy, and the
exact position on the chip. This means that for different galaxies
on the same chip we may derive different sky values.
In deep surface photometry the quality (flatness and noise)
of the background around (and "below'') the galaxy determines
the surface brightness level down to which one
can trust the profiles.
A common way of measuring the sky is, after the removal of a possible large scale
gradient (typically of only first order), to manually place several
small boxes homogeneously around - but outside - the galaxy,
avoiding foreground stars or obvious background galaxies, and
measure the median of the pixel distribution in each box. The best
sky value is then the mean value of all median measurements.
However, the fact of storing SDSS data as integer not real numbers
(cf. Sect. 3.1) hampers the use of median values in small boxes.
Only by using a large number of pixels (or an inappropriate high
number of boxes dealing with about 100 galaxies) one is able to recover
an accurate estimate of the mean value of the background pixel
distribution.
Therefore we decided to use two independent methods to determine
the sky value. First, we strategically placed 2-5 large, rectangular
sky boxes (of roughly 100 k-200 k pixels) as close as possible to the
galaxy avoiding bright foreground stars or obvious structure in
the background (e.g. from halos of very bright foreground stars)
while trying to match the brightness of the sky around the galaxy.
Within each box we derived the mean sky after three,
,
clipping
iterations to remove the unavoidable contamination by faint foreground
stars. The mean value of all boxes serves as the first estimate of
the sky.
For the second method we applied a free ellipse fit to the original
image. Using the ellipse task in IRAF
we calculated the flux in linear steps of 10 pixels between successive
ellipses forcing the program to extend the fit well beyond the galaxy
with the fixed ellipticity and PA of the outer disk (see
Fig. 2). By plotting the flux at these ellipses as
a function of radius it becomes clear at which radial distance the ellipses
leave the galaxy and enters the background, flat flux (noise), region. After
visual confirmation that these ellipses are really outside the galaxy,
by overplotting the ellipses on the image, the mean value and standard
deviation of the fluxes within the above radius and the radius extended by
20% are used as the final sky values.
In most cases the two methods agree well within
0.15 counts
(
0.15% of the sky). Since it is possible to automatise it,
we choose the ellipse method to fix our final sky values. They are
listed in Table 2 together with a limiting surface
brightness (
)
due to a
-sky error, which
is used to constrain the outer boundary for the exponential fits.
Our sky values can be easily inspected by downloading the public
SDSS images.
To specify the error on the profiles from our sky estimate
(which is much larger than the statistical errors produced
by e.g. photon noise) in more detail we defined a more conservative
critical surface brightness (
)
up to where
we really trust the final profile.
This is placed where the profiles obtained by either over- or
undersubtracting the sky by 
start to deviate by more
than 0.2 mag, which is at 0.54 mag above the limiting surface
brightness defined above.
So the typical value for the full sample of this critical surface
brightness is
-mag/
.
This is the limit down to which the slope of the outer profile could
be traced confidently.
![\begin{figure}
\par {\hspace*{2mm}\includegraphics[width=5.6cm,angle=0]{4883f003...
...4883f004.ps}\par\includegraphics[width=5.7cm,angle=270]{4883f005.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg145.gif) |
Figure 2:
Sky obtained by ellipse fitting:
upper panel:
-band image of NGC 5300 exemplary
overlayed by eight fixed ellipses at every 100 pixels in the range
300-700 pixels. The white rectangular regions are masked areas.
Middle panel: mean isophotal intensity (in counts) of
the fixed ellipses fitted every 10 pixels. The region between
the vertical dashed lines is used to determine the sky value
(
), which is indicated as a horizontal
dashed line together with the two dotted lines at  .
Lower panel: final surface brightness profile (circles)
overlayed by the four profiles obtained by either over- or
undersubtracting the sky by 
(triangles) or
by
(squares).
The horizontal dashed line gives the critical surface brightness
(
)
up to where we trust the profile i.e. where
the
profiles deviate by more than 0.2 mag.
|
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The pure background noise in the
band images is typically slightly
higher compared to the
band image, which is expected for images
taken at new moon. However, the
band images suffer often from an
electronic noise pattern in addition to the normal patchy background.
Typically 6-8 more or less pronounced stripes are visible where all
rows show a slightly different background level, alternating between
being higher or lower. Unfortunately, this structure is not common on
all images so there is no way to properly remove it by combining
several images as usually done for fringe patterns. In many cases the galaxies
are small compared to the strip size and the above pattern is not an issue.
In other cases only small parts of the galaxies reach another
strip and can be masked. However, there are some galaxies extended over
two or more stripes. For these systems the sky estimate is less
reliable because the contribution of each region changes with
changing size of the ellipse.
For five galaxies (NGC 1042, NGC 1084, NGC 5480, NGC 5624, and
PGC 006667) we had to remove at first a large scale gradient (from
top to bottom) in the background of the
band images (for NGC 1042
also in the
band) with a linear fit (using IRAFs imsurfit).
![\begin{figure}
\par\includegraphics[width=5.5cm,angle=270]{4883f006.ps}\\ [2mm]
\includegraphics[width=5.5cm,angle=270]{4883f007.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg146.gif) |
Figure 3:
SDSS quality check: azimuthally averaged, radial surface
brightness profiles obtained from SDSS images (
band with
big circles;
band with big triangles)) are compared with much deeper imaging
(thin, continuous line) presented in Pohlen et al. (2002).
The small squares are obtained by using the transformation
to convert SDSS
and
into standard Johnson R band
(used by Pohlen et al. 2002) following Smith et al. (2002). |
Open with DEXTER |
We have checked our sky estimation method comparing the profiles obtained
from the SDSS images with deep surface photometry. We have used the
profiles of three face-on Sbc-Sc galaxies from Pohlen et al. (2002), from
which UGC 9837 is also part of our sample.
The photometrically transformed SDSS profiles match the deep R-band surface
brightness profiles in all three cases quite well (two of the galaxies are
shown in Fig. 3). The remaining differences visible are easily
explained by the two very different methods applied to extract these profiles.
Whereas the SDSS profiles are standard fixed ellipse fits to the images, the
deep R-band comparison profiles are obtained by vertically averaging after
polar transformation (see Pohlen et al. 2002). This test confirms that SDSS
profiles can be obtained reliably down to
-mag/
.
3.5 Ellipse fitting and masking
We used the IRAF task ellipse (STSDAS package) on the sky
subtracted images to produce our final surface brightness profiles.
We apply an extensive manual masking for each galaxy image. This is
necessary to remove contamination from different sources.
We masked all non-galaxy components like foreground stars, companion
galaxies, or faint background galaxies. Not masked are extended spiral
arms, or outer asymmetries clearly belonging to the galaxy itself.
The masking is primarily done in a
pixel (
)
median smoothed version of the image, ideally suited to visualise
structure in the background. This step also ensures to reliably
trace the halos of the foreground stars to large radii.
Whereas this is necessary for bright stars it is a conservative measure
for fainter ones. In a second round any remaining stars in the unsmoothed
image are also masked.
The common center for each concentric ellipse is fixed by a Gaussian
fit to the bright nucleus of the galaxy. For 21 galaxies (marked in
Table 2 with a
)
the disk is lopsided or
there is no bright center visible so we first allowed the ellipse
centers to vary, choosing the best center representative for the
outer disk.
We used a logarithmic radial sampling with steps of 0.03 to increase
the S/N especially in the outer parts at cost of larger radial bins
compared to linear sampling. Iterative
rejection along the
ellipse is applied to minimise the influence of cosmic rays or
any remaining faint foreground stars.
We fitted two different sets of ellipses (three in case of a
necessary free center fit) to each galaxy image (for general
information on ellipse fitting see Erwin et al. 2006). The first,
free ellipse fit tends to follow morphological features like
bars, spirals, or asymmetries so it is not ideal to characterise
the outer, underlying disk component, which we want to address in
this work. Therefore we used a fixed ellipse fit to produce our
final surface brightness profiles which will be the only ones
discussed in the following sections. Fixing a single ellipticity and
position angle for a galaxy is based on the assumption that the
disk is axisymmetric and round and the ellipticity and PA values
are representative for the orientation (inclination angle) of the
galaxy.
The initial free ellipse fit (fixed center, free ellipticity and PA)
is used to determine the best set of ellipticity and PA describing
the outer disk. These values are typically taken at the radius where
the mean flux of the best fitted free ellipse reaches the value of
the standard deviation of our background measurement in large boxes
(
criterion).
This limit ensures enough S/N to fit a free ellipse but is small enough
to be in the radial region dominated by the outer disk.
Ideally one would like to determine the ellipticity and PA
of the outer disk not photometrically, but by means of kinematical
informations. Since this is not possible for the whole sample
we used only the photometric way to get a set of homogeneous values
for all our galaxies. However, for some galaxies the
criterion
clearly marked a radius in a region with rapidly changing ellipticity
and PA values, or a region which is not representative of the outer disk.
In this cases we chose, after visual inspection, a different radius to
represent the disk, which is typically the outermost successfully
fitted free ellipse.
The
band and
band ellipticity and PA values
are determined independently. Since a galaxy should have only a single
pair of PA and ellipticity (depending on the inclination and intrinsic
circularity) independent of the wavelength used, we averaged the
two values in case of no major problem in one of the bands.
The fixed ellipse fits to the
and
band is
therefore repeated using these mean values (see Table 2)
and the resulting profiles are shown in Appendix A.
4 Analysis
4.1 Classification
![\begin{figure}
\par\includegraphics[width=7.0cm,angle=0]{4883f008.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg151.gif) |
Figure 4:
Classification schema (following Erwin et al. 2006): The
three main disk types according to break features in their surface
brightness profiles are
Type I (no break), Type II ( downbending break),
and Type III ( upbending break).
In case the galaxy is barred (SB/SX) the downbending
breaks (Type II) are subdivided according to the position of
the break in respect to the bar:
Type II.i (inside) or Type II.o (outside).
An additional level of subclassification is applied for this
class trying to relate the observed break to a physical origin.
These are Type II.o-AB, Type II.o-OLR, and Type II.o-CT (see text).
For apparently unbarred galaxies (SA/S?) we use only Type II-CT or
Type II-AB.
The upbending breaks (Type III) are subdivided according
to the possible nature of the outer region: (d)isk- or
(s)pheroid-like.
Some galaxies are better described with two breaks, each of
which could be associated to one of the individual types.
They are assigned a mixed classification (e.g. Type II-CT + III).
|
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We have classified (following Erwin et al. 2006) each profile according
to observed break feature using the following nomenclature: Type I
(no break), Type II (downbending break), and Type III (upbending break).
A schematic view of our classification is shown in Fig. 4.
Images and profiles for some typical examples of each class are given
in Fig. 5.
The Type I classification follows the nomenclature established by
Freeman (1970). Aside from a varying bulge component these galaxies exhibit
a region well described by a single exponential allowing for some wiggles
associated with substructure in the disk such as spiral arms or prominent
star forming regions.
The galaxies displaying a break with a downbending steeper outer
region could be labelled
Type II as (Freeman 1970) originally proposed. Although he states at
some point the inner deficit is not far from the center of the system
there is no further restriction on this distance. In addition, for the three
most prominent Type II galaxies in his sample he states that the outer
exponential disk begins outside the main region of spiral-arm activity,
so clearly outside a central region.
Following Erwin et al. (2006) the Type II class is subdivided
into two groups in case the galaxy is barred. A Type II.i (inside)
and a Type II.o (outside) depending on the position of the break in
respect to the bar length (inside or outside the bar region).
Moreover, we tried to subclassify the Type II and Type II.o profiles
even further into additional three groups, which now tend to
categorise the observed profiles according to their potential
physical origin.
First, profiles where the apparent break can be associated with
large scale asymmetries of the galaxy in itself (only present
in Sc-Sd galaxies). These are either associated to a lopsided disk
having a well defined center, which is different from the applied
ellipse centered on the outer disk, or to some large scale asymmetries
in (or beyond) the main body of the outer disk (cf. extended spiral arms).
These profiles are called Type II-AB, for Apparent
(or Asymmetric) Break.
Another group, showing the break radius at around 2-2.5 times the
bar radius, is probably related to a resonance of the bar as described
in Erwin et al. (2006). The bar itself is most often nicely marked by the
presence of an additional inner ring.
These profiles are classified as Type II.o-OLR, for Outer
Lindblad Resonance which happens to be at the
position of
2 times the bar radius.
The remaining profiles revealing a broken exponential behaviour
are called Type II-CT, since they are best associated to what we
call now Classical Truncations discovered by
van der Kruit (1979). Three nice examples of unbarred Sbc-Sc face-on
galaxies are presented by Pohlen et al. (2002).
For Type II-CT galaxies with bars we made sure that the break is
significantly further out than typical for the Type II.o-OLR breaks.
The galaxies with a break followed by an upbending (shallower outer)
profile are
called Type III according to Erwin et al. (2005a) who find two
sub-classes. One (Type III-s) showing a fairly gradual
transition and outer isophotes that are progressively rounder
than the isophotes in the main disk, suggesting a disk embedded
within a more spheroidal outer zone associated to a halo or an
extended bulge component. The other type (Type III-d)
exhibits a rather sharp transition with the outer isophotes being
not significantly rounder.
Whereas measuring the ellipticity is an appropriate way to
disentangle for early-type galaxies, devoid of prominent
spiral arm structure misleading the free ellipse fits, it
will most probably fail for late-types. So we decided here
to classify them all as Type III only subclassifying those
with visible spiral arm structure beyond the break radius,
obviously associated with an outer disk-like region,
as Type III-d (cf. Appendix A).
In our subsequent paper we will study if colour variations
at and beyond the break could potentially be used to decide
between these subclasses. The colour profile of a transition
between a star-forming inner disk and a halo/envelope
(Type III-s) may look different from a transition
between an intermediate-age inner disk to a predominantly
younger outer disk (Type III-d).
Some galaxies have a more complex surface brightness
distribution. They are better described with two breaks
each of which could be associated to an individual
type (as described above). These are called mixed
classification (see Fig. 5).
For all the galaxies with a break in the profile we verified
that changes in the sky value (e.g. subtracting
to the sky level) will not produce an untruncated Type I
profile (see Fig. 2).
![\begin{figure}
\par\includegraphics[width=5.4cm,angle=270,clip]{4883f009.ps}\inc...
...883f015.ps}\includegraphics[width=5.4cm,angle=270,clip]{4883f016.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg152.gif) |
Figure 5:
Prototypical examples for each class of profiles:
Type I, Type II-CT, Type II.o-OLR, and Type III (top to bottom).
Left panels:
-band images (unrotated cut-outs
from the SDSS fields) with the break radius marked with an ellipse.
The ellipse for the first Type I
galaxy corresponds to the noise limit at 140''.
Right panels: azimuthally averaged, radial SDSS surface
brightness profiles in the
(triangles) and
(circles)
band overlayed by
band exponential fits to the
individual regions: single disk or inner and outer disk.
In addition we show the critical surface brightness
(
)
for each band (dotted and dashed
horizontal lines), down to which the profile is reliable
(see Appendix A for a detailed legend).
|
Open with DEXTER |
![\begin{figure}
\par\includegraphics[width=5.5cm,angle=270]{4883f017.ps}\includeg...
...]{4883f023.ps}\includegraphics[width=5.5cm,angle=270]{4883f024.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg153.gif) |
Figure 5:
continued.
The ellipse for the first Type II.i galaxy corresponds to
the inner boundary at 20''. For the mixed classifications
two ellipses are shown corresponding to the associated breaks.
|
Open with DEXTER |
Please note that our classification Type I and Type II are used
slightly different from MacArthur et al. (2003). Our Type II-CT class
is called Type I with truncation in their study and their Type II
is a mix of our Type II.i and all other Type II.o classes. Since we
do not have infrared images we cannot comment on their "transition''
class. However, we note that for IC 1067 (see Appendix A
for a detailed discussion) the
-band profile is barely
consistent with being Type I whereas in the
-band
it is clearly a Type II.o-OLR which is consistent with the profile
shown by Erwin et al. (2006). This might imply that in very few
cases dust is playing a role in shaping the observed profile
close to the center. So this profile could be a Type I
in the K-band, which has to be investigated in further
studies.
4.2 Deriving break radius, break region and scalelengths
In addition to our pure identification - break (down- or up-bending)
yes or no - we have quantified the radial distance
where the break occurs, characterised its sharpness and derived
an inner and outer scalelength (
,
) (see Fig. 6).
To determine the scalelengths we restricted our fits to the 1D,
azimuthally averaged, surface brightness profiles obtained with
fixed ellipse fits (cf. Sect. 3.5). Since a detailed bulge
to disk decomposition is beyond the scope of this paper, we used
the so called "marking the disk'' method by applying boundaries
and fitting simple exponential functions:
.
The inner boundary (b1) is chosen manually to exclude the region
obviously dominated by the bulge plus bar (shoulder) component.
The outer boundary (b4) is taken where the surface brightness
profile reaches (
)
of the noise level obtained from the
sky ellipse fitting described in Sect. 3.3.
If the profile shows a broken exponential we need an additional
boundary marking the break. This could be placed by eye, but to
obtain the break radius objectively we used the following approach.
At first an approximated derivative of the profile is calculated
at each point, by fitting a straight line including four points
around each radius. This provides a measure of a local scalelength
(
) along the radial axis (cf. Fig. 6).
To get a linear spacing of surface brightness measurements along
the radial axis and to decrease the noise in the
distribution
we first rebinned the profile to linear units using a spline function
and then median smoothed the
profile adapting the smoothing
length to
of the full extent of the profile.
Our general assumption is now that we have two regions with
nearly constant scalelength together with a change (up- or downbending)
in the profile. This will be reflected by two plateaus in the plot
of
(see Fig. 6). Depending on the actual shape
(e.g. sharpness) of the transition region
will move from
one scalelength region around
to another region around
.
To quantify a single radius defining this break we used then
the radius where the
profile crosses the horizontal line set
by a characteristic value. In case the two regions do not cover
the same radial range, the characteristic value is always taken
as the median of the
distribution, to avoid a bias
towards the more extended region.
To characterise the shape of the break we defined an additional
region around the break. Ideally a sharp break would translate into
a step function in the
profile whereas a smooth transition
would cross the line set by the weighted mean value with a finite
slope. Therefore we defined an inner and outer boundary of the
break region where the profile, starting from the break, reaches
a value within two standard deviations away from the mean calculated
for the inner/outer region separately (cf. Fig. 6).
The derived break radii are almost always consistent with those
derived by eye, but of course fail if one of the regions is very
small (e.g. in the case of IC 1067, see Appendix A)
or get uncertain if more than two regions with roughly constant
scalelengths are involved (as for the mixed classifications, see
below and Sect. 5).
Using the boundaries of the break region (b2 and b3)
to mark the separation of an inner and outer exponential disk,
the final scalelengths are derived from two simple exponential fits
(
and
)
to the original profile.
To decrease the noise we give priority to this classical approach
to determine the scalelength over using a weighted mean from the
values inside the now defined inner and outer region.
Fitting the two exponentials one could alternatively define
the break radius, as the meeting point of the two exponential
fits. However, since this would add an influence by the actual
shape of the two disk regions into the positioning of the break
radius we decided against it.
In cases where the derivative profile (
) crosses the
horizontal line set by the characteristic value twice (three
or more times is considered to be explained by wiggles caused
by asymmetries such as spiral arms) we check if we could apply
a mixed classification. This implies assigning two breaks associated
to the individual types as discussed in Sect. 4.1
which significantly improve the overall fit. The boundaries for
both breaks are then used to fit three exponential regions.
The final results for all the galaxies are given in Table 3.
We do not provide individual errors for the fitting parameters in
Table 3, since their uncertainty is a complex
combination of random and systematic errors.
Typical random errors of the exponential fitting routine alone are
2% for
, 3% for
,
mag for
,
and
mag for
.
The uncertainty in the sky subtraction, however, translates to
a clearly systematic error. In the case of over/under-subtraction
the measured scalelengths are systematically smaller/larger and
the central surface brightnesses are systematically lower/higher.
To estimate how the error on the sky subtraction alone effects
our parameters we have over/under-subtracted the measured sky
level by
.
Typical errors are then only
for
and
mag for
, but
for
and
mag for
.
Another source of uncertainty is generated by the positioning of
the boundaries (b1-4). This uncertainty can not be easily
quantified since it depends on the shape (up/down-bending) of,
and features (bulges, bars, etc.) in, the surface brightness
profiles and cause systematic errors. To minimise their
contribution in our determination of the structural
parameters each fit is verified by eye.
![\begin{figure}
\par\includegraphics[width=6.1cm,angle=270]{4883f025.ps}\par\includegraphics[width=6.1cm,angle=270]{4883f026.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg167.gif) |
Figure 6:
Example of how to establish the break radius, the
break region and the associated scalelengths: upper panel:
azimuthally averaged, surface brightness profile, overlayed by the
best fitting exponentials (with scalelengths
and
) marking
the position of the boundaries (b1-4) and the break radius
.
Lower panel: approximated derivative (crosses) of the
profile providing a local scalelength (
) together with
the rebinned and smoothed version (triangles). The
horizontal dashed line marks our characteristic (or mean) value
which is the median of the
distribution. The
vertical dotted lines mark the inner and outer boundary of
the break region. |
Open with DEXTER |
5 Results
Our final classifications are presented in Table 3
and discussed in more detail individually in Appendix A.
For four galaxies in common with Erwin et al. (2006) the classification
(as well as the final profiles) agree very well.
All features in the surface brightness profiles classified here
are always consistently found in deep surface photometry profiles
available (cf. Appendix A) in the literature
(e.g. Courteau 1996).
About 90% of our sample can be classified into one of
the classes described in Sect. 4.1. However, the
remaining galaxies are better described with two breaks in
their surface brightness profiles. Galaxies with extra
breaks are classified as mixed.
In almost all cases this is a combination of a downbending
break, either Type II-CT, Type II.o-OLR, Type II-AB, or Type II.i,
classified as described in Sect. 4.1, followed by an
additional upbending break in the very outer parts. These
galaxies are classified as e.g. Type II.o-OLR + III.
Interestingly, none of the Type III profiles show an additional
outer truncation within our sensitivity limit.
Only two galaxies (see detailed explanation in Appendix
A) exhibit an inner downbending break followed
by an additional outer downbending break. In one case
(NGC 4517A) the outer sharp drop is clearly associated to a
Type II-AB, whereas the inner break is consistent with being a
Type II.o-OLR or Type II-CT.
The other case is NGC 4210, where the inner boundary of an extended,
exponential, break region is consistent with a Type II.o-OLR break leaving
the outer break to be Type II-CT. This galaxy could be the ideal test
object to study the difference between Type II.o-OLR and Type II-CT breaks.
Finally, for only one galaxy, IC 1067, the classification in
the
and
-band could be different
(see Sect. 4.1).
The vast majority (almost 90%, see Table 4) of the galaxies
exhibit surface brightness profiles with breaks, only 9 (
)
are reasonably well described (allowing sometimes for quite extensive
deviations) as being purely single-exponential (Type I).
Even adding the barred galaxies showing only a dip inside the bar
radius (Type II.i), their frequency increases up to merely
.
of the galaxies are classified as Type II with a break
and downbending profiles (
excluding Type II.i). The frequencies
of the three main subgroups are the following:
a)
(from the full sample) exhibit a classical
truncations (Type II-CT);
b)
(from the full sample) are classified as having
breaks with downbending profiles that could be (size wise) related to
the presence of the bar (Type II.o-OLR); and
c)
(from the full sample) show breaks in their profile
(Type II-AB) that could be originated by a lopsided or asymmetric disk,
not allowing us to probe for a real, intrinsic break in the stellar
light distribution using our azimuthally averaged, fixed ellipse fits.
of the galaxies show a break with an upbending
profile (Type III).
Table 4:
Frequency of disk types: listed are the number of galaxies
per profile type. The values in brackets are those associated to more
than one break type (mixed classification). Therefore the last column
gives the frequency for each break type and does not add up to 100%.
In the following we give all measurement of lengths and ratios
as obtained for the
band and excluding the mixed
classifications if not otherwise stated.
The mean central surface brightness and scalelength of the 9 Type I
galaxies are
-mag/
and
kpc respectively, which are typical values for local galaxies
(cf. MacArthur et al. 2003; de Jong 1996).
We confidently trace the profiles down to our critical surface
brightness of
-mag/
(see Fig. 2). So, in terms of scalelength we do
not find a break down to 6-8 times the measured scalelength.
The break in the surface brightness profiles appears at
kpc and ranges between 5.1 kpc
and 14.7 kpc with a slight trend towards galaxies with higher
luminosities having larger break radii (cf. Fig. 7).
![\begin{figure}
\par\includegraphics[width=5.5cm,angle=270]{4883f027.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg184.gif) |
Figure 7:
Break radius (
) in absolute units (kpc) versus dynamical
mass (
)
and absolute magnitude (
) in the B-band according
to LEDA for the different break types: Type II-CT (upper row),
Type III (middle row), and Type II.o-OLR (bottom row).
Overplotted are robust linear fits (dashed lines) to guide
the eye and in the lower right corner of each plot the Spearman
rank correlation coefficient. The break radius correlates
in all three cases with absolute magnitude. With the exception
of the Type II-CT, the relation of the position of the break with
the dynamical mass is less tight. |
Open with DEXTER |
We do not find a systematic difference between the break
radii as measured in the
or
band.
In relative units the break is at
times the inner
scalelength with values between 1.4 and 4.2, uncorrelated
with rotational velocity and with a weak trend towards higher
values for brighter galaxies (cf. Fig. 8).
![\begin{figure}
\par\includegraphics[width=5.5cm,angle=270]{4883f028.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg186.gif) |
Figure 8:
Classical truncations (Type II-CT): break radius in units of
inner scalelength versus
absolute magnitude (
) (left, upper panel),
rotational velocity (
) (left, middle panel),
extinction corrected central surface brightness of the
inner disk (
) (left, lower panel),
break radius in linear unit (
) (right, upper panel),
inner scalelength in linear unit (
) (right, middle panel),
and Hubble type (T) (right, lower panel). Overplotted are
robust linear fits (dashed lines) to guide the eye and in the
lower right corner of each plot the Spearman rank correlation coefficient.
|
Open with DEXTER |
The value found here for the position of the break in terms of
radial scalelength is apparently smaller (although compatible
within 1
)
to the one
quoted for three galaxies by Pohlen et al. (2002):
.
According to Pohlen et al. (2002), the one galaxy in common (UGC 9837) has
a value of 3.1 for
, which is consistent with our ratio of 2.7
obtained from the SDSS image.
The two galaxies with high values (4.3 and 4.2) are too distant to
be in our sample and both are intrinsically large, having break
radii of 14.7 kpc and 21.1 kpc.
Fitting the SDSS profile (converted to Johnson R according to
Sect. 3.2, see Fig. 3) and using our method
for one of them (NGC 5923), we obtain also a consistent value
(4.1 compared to 4.3 quoted by Pohlen et al. 2002).
Due to the completely different masking of a very close extended
companion the comparison for the third galaxy (NGC 5434) is
not straightforward (3.2 compared to 4.2).
So neither their larger intrinsic size nor a systematic error in
determining the ratio (
) is responsible for the apparent
mismatch of the mean values for the two samples, suggesting that
its origin is due to small number statistics.
However, our mean value of
is significantly lower compared
to the
value obtained for 16 face-on galaxies by van der Kruit (1988).
This large offset is almost certainly due to the different
definition (break versus cut-off) and method used to mark the
truncation. We determine the truncation at the position of the
measured break in the profile (so quite far in), whereas
van der Kruit was looking for a sharp outer boundary estimated
from isophote maps.
Our value is supported by Bosma & Freeman (1993) who stated that for
7 galaxies (with breaks in their surface
brightness profiles), of the 21 reported by Wevers (1984) (so virtually
the same dataset van der Kruit 1988 used), the mean value of the
break to scalelength is
,
so very close to our mean value.
The mean scalelength of the inner disk
in our sample
is
kpc and ranges between 2.0 kpc and 6.6 kpc,
which is typical for local galaxies (cf. MacArthur et al. 2003; de Jong 1996).
The central surface brightness (extrapolated from the fitted inner
exponential, corrected for galactic extinction, but uncorrected
for inclination) ranges between
-mag/
and
-mag/
(
18.9-22.8
-mag/
) with a clear trend towards galaxies
with fainter luminosities having a fainter central surface
brightness (cf. Fig. 9) as seen by MacArthur et al. (2004)
or de Jong (1996).
![\begin{figure}
\par\includegraphics[width=5.5cm,angle=270]{4883f029.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg194.gif) |
Figure 9:
Classical truncations (Type II-CT): extrapolated central surface
brightness (open circles) and surface brightness at the break
radius
(filled squares) in the
band versus
absolute magnitude (
) in B according to LEDA. Overplotted are
robust linear fits (dashed lines) to guide the eye and in the
lower and upper right corner the Spearman rank correlation coefficient
for each data set. |
Open with DEXTER |
However, the surface brightness at the break radius only
weakly correlates with absolute magnitude (cf. Fig. 9)
and peaks (cf. Fig. 10) at a mean value of
-mag/
(
-mag/
).
![\begin{figure}
\par\includegraphics[width=5.5cm,angle=270]{4883f030.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg197.gif) |
Figure 10:
Histogram of the surface brightness (in the
band) at the
break radius for the galaxies of Type II-CT (solid line),
Type III (dashed line), and Type II.o-OLR (dotted line). |
Open with DEXTER |
The mean ratio of inner to outer scalelength is
with a mildly peaked distribution ranging between
.
The break radii for the Type II.o-OLR breaks span a wider range,
compared to Type II-CT breaks, between 2.4 kpc and 25.0 kpc
(mean:
kpc) again with a clear trend towards
galaxies with higher luminosities having larger break
radii (cf. Fig. 7).
In terms of inner scalelength almost all breaks appear in
the small range between 1.4-2.4 times
(with a mean
at
), except for one galaxy (NGC 5430) where the
break is at
but which could be also classified
as Type I with bumps shaped by the prominent bar
(cf. Appendix A).
The surface brightness at the break radius is
-mag/
.
Although on the lower end compared to the distribution
for
and
, neither of these parameters
works out as a clear discriminatory property for the two different
downbending break types Type II-CT and Type II.o-OLR.
In relative units the Type III break appears further out, compared
to Type II-CT or Type II.o-OLR breaks, at
times the inner
scalelength with values between 3.7 and 5.8 (excluding the
seven galaxies with mixed classifications where an inner scalelength
is not well defined).
However, in absolute units they span the same range. The break
appears at
kpc and ranges between 4.4 kpc
and 15.5 kpc having the same trend with
luminosity (cf. Fig. 7).
The inner scalelength is on average smaller
with
kpc ranging only between 0.9 kpc and
3.0 kpc.
The central surface brightness (extrapolated from the fitted inner
exponential and corrected for galactic extinction) ranges only
between
-mag/
and
-mag/
(mean:
-mag/
)
without showing the clear trend with luminosity as for the
Type II-CT breaks.
The mean value for the surface brightness at the break radius,
-mag/
(
-mag/
for the seven galaxies
with additional downbending breaks inside), is clearly fainter
compared to the Type II-CT breaks (see Fig. 10).
Plotting the frequency of break types versus the Hubble
types (grouped in three bins: Sb-Sbc, Sc-Scd, and Sd-Sdm)
reveals a clear correlation (cf. Fig. 11).
![\begin{figure}
\par\includegraphics[width=5.5cm,angle=270]{4883f031.ps}\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg212.gif) |
Figure 11:
Frequency of profile types Type I (open circles),
Type II-CT (filled squares), Type III (open triangles), and
Type II.o-OLR (open squares) in relation to the Hubble type. The
galaxies are merged in three morphological bins (T between 2.5-4.4,
4.5-6.4, and 6.5-8.4). The associated points are connected with lines
and slightly shifted in T to be able to separate them. |
Open with DEXTER |
Whereas the few Type I galaxies are evenly distributed
with Hubble type, the frequency of Type III breaks
decreases, and that of the Type II-CT increases, with later
Hubble type.
The Type II.o-OLR breaks appear to have a minimum for the Sc-Scd
galaxies which might be related to a minimum in the overall
RC3 strong bar frequency for Sc galaxies as mentioned by e.g.
Lütticke (1999).
We know that the Hubble type T correlates with absolute magnitude
(cf. Sect. 2.1), but marking the different break
types in such a plot shows that the correlation of break type
is more pronounced with the Hubble type compared to
.
For the classical truncations (Type II-CT) the position of the break at
times the inner scalelength shows a trend with Hubble
type (cf. Fig. 8) in the sense of later types being
earlier truncated. However, it seems to be almost uncorrelated
with total mass (either measured with
or
,
see
Fig. 7).
We find for some of our Type III galaxies indication for a
recent interaction (cf. Appendix A) such as
close physical companions, streams, or shells. However, using
the number of neighbours (as determined in Sect. 2.2),
to characterise the environment, we do not find a clear correlation with
the profile type.
Although it looks like the Type III galaxies tend to have more
neighbours within a 1 Mpc volume (59% have 3 or more neighbours while for the Type II-CT
the fraction is only 35%), such a correlation
is far from being clear-cut. There are still many classical truncations
among the galaxies having three or more (even up to nine) neighbours as
well as Type III galaxies without any companion.
However, we have the problem that criteria for environment
are often too crude and lead even to controversial results.
For example, our prototypical classical truncation, NGC 5300, has
five neighbours in the SDSS database, which is clearly in a denser
region according to our environment criterion. Using the CfA catalogue
and applying a different criterion Varela et al. (2004) list it as being
part of their truly isolated galaxy sample.
6 Discussion
As reported by Pohlen et al. (2004) we also do not find any galaxy with
a sharp cut-off in the radial light distribution. This means that
the so-called truncated galaxies are best described by a broken
exponential. This seems to be now the intrinsic structure
associated to the inferred sharp cut-offs proposed by van der Kruit (1979).
A similar result is found, using a completely independent approach, by
Ferguson et al. (2006) mapping the prototypical truncated galaxy M 33. They
traced the profile down to
I-mag/
(transformed to surface brightness) using star-counts.
In general, the shape of the transition regions we found (measured in
terms of the boundary difference
b3-b2) is no longer as sharp
as measured by Pohlen et al. (2002). Only very few cases
(e.g. NGC 5300 or NGC 7437) exhibit a very sharp transition between
the inner and outer disk region. Most often the Type II-CT breaks appear
with a more gradual transition zone up to an almost exponential region
of size
4 kpc in between.
Since the discrimination between Type II.o-OLR and Type II-CT is solely
based on bar size measurements one could argue that there
are some undetected Type II.o-OLR breaks among the galaxies classified
as Type II-CT.
However, we carefully use either bar sizes from the literature or in
most cases estimated them from the image to make sure the Type II-CT
is as good as possible separated from the Type II.o-OLR breaks.
In total, without specifying the origin, most of the galaxies
(
60%) exhibit a break followed by a downbending profile
almost consistent with the edge-on results by Kregel et al. (2002),
although they probably would have excluded the Type II-AB galaxies
from their initial sample.
We do not find truncation breaks beyond
-mag/
(cf. Fig. 10). We have explored whether this could be an
observational bias caused by the difficulty of detecting breaks at faint
levels. To do that we simulated 2D galaxies with breaks in their surface
brightness distribution at different surface brightness levels. These
galaxies are added to the real sky background and we measured the
breaks as for real galaxies. From this we estimate our limit for detecting
breaks of
-mag/
.
This limit leaves a range of
1 mag to reach our critical surface
brightness of
-mag/
(down to
which the slope
of the outer profile could be traced confidently, see Fig. 2).
So we expect to detect all truncations in the region
-mag/
if they do exist. Consequently, the
decline observed in Fig.10 seems to be real.
In addition, in terms of scalelength the largest break we find is
at
,
but we are able to trace the profiles of our
Type I galaxies down to
6-8 radial scalelength.
So we think that we do not miss any truncation breaks due to
the limiting depth of the SDSS data and our Type I galaxies are
indeed untruncated.
This is consistent with measurements on individual galaxies being
intrinsically untruncated down to
10 scalelength
(e.g. Bland-Hawthorn et al. 2005; Weiner et al. 2001).
One of the key questions is now to find why some galaxies show
truncations and (the minority) does not.
The strong increase for the Type III frequency towards earlier Hubble
types (Sb-Sbc) could be used to argue against the Type III feature
being really related to the disk itself, by explaining the rise
in the profile as a traditional R1/4 bulge component taking
over from the exponential disk in the outer parts.
However, Erwin (2005) already showed that this is only true
for about
1/3 of the earliest types (SB0-SBb, having the
highest chances of being bulge dominated). We see that
40%
of our type III late-type galaxies exhibit clear signs for spiral arms in the
outer disk excluding any spheroidal (pressure supported) nature
of the outer structure. For another
23% of the Type III
galaxies we do not find a significant decrease in ellipticity (expected
if produced by a spheroidal component) while fitting free ellipses
across the break. So we conclude that in most (>63%) of our
Type III galaxies the outer region is indeed related to the disk.
This results fits nicely to the extended outer (star-forming) disks
(e.g. NGC 4625) which have been recently reported by the GALEX
team (Thilker et al. 2005; Gil de Paz et al. 2005) as being significantly more
frequent than thought before.
Unfortunately, we do not have any galaxy classified as Type III on
our SDSS images in common with those reported by the GALEX team.
However, the profile shown by Swaters & Balcells (2002) of NGC 4625 clearly
suggests a Type III classification.
7 Summary
The main goal of our study is to provide a census of the
radial disk structure of local (
km s-1)
late-type galaxies.
Using the LEDA catalogue we selected a complete sample of
655 galaxies down to
=-18.4 B-mag. 98 (85 with
useful images) of them are part of the SDSS Second Data
Release (DR2) which provides the imaging data used here.
After careful sky subtraction we
obtained the radial surface brightness profiles from
fixed ellipse fits. We classified the resulting profiles (following Erwin et al. 2006)
searching for clear breaks either of the downbending
(steeper outer region) or upbending kind (shallower
outer region) and derived
scalelength and central surface brightness values for
exponential fits to the individual regions.
The main conclusions are as follows:
- 1.
- We are able to reliably trace azimuthally averaged, fixed ellipse
profiles of face-on to intermediate inclined galaxies down to a critical
surface brightness of
-mag/
using SDSS
imaging data.
We have taken extreme care in determining the background (sky) around
our objects. Our surface brightness limit value is supported by finding
similar sky values with different methods. In addition, our profiles match
those from available deeper photometry and we are able to recover
simulated profiles added to empty SDSS sky fields down to the above
surface brightness limit.
- 2.
- 90% of our galaxies could be classified into one of the following
classes - Type I (no break), Type II (downbending break), and Type III
(upbending break) - extending Freemans original classification.
The remaining 10% of the sample
could be well described being a mix from two individual classes. We introduced
two main sub-classifications for the Type II class connecting the observed break
with possible different physical origins: Type II-CT, classical truncations,
probably associated with a global, radial star-formation threshold
(cf. Sect. 1), and exclusively for barred galaxies, Type II.o-OLR
,
OLR breaks, observed at around twice the bar radius and probably
associated with the outer Lindblad resonance of the bar
(see Erwin et al. 2006).
- 3.
- Surprisingly only
15% of all galaxies have a normal
purely exponential disk down
to our noise limit. A good deal more (
of each) have
profiles with an upbending break (Type III) or a classical
truncation (Type II-CT).
- 4.
- We find a correlation of break type with morphological type.
Classical truncations (Type II-CT) are more frequent in later
types while the fraction of upbending breaks rise towards
earlier types.
- 5.
- Our Type I galaxies seem to be genuinely untruncated.
The exponential profiles extend reliably down to a surface
brightness of
-mag/
(equivalent to
6-8 times the scalelength).
- 6.
- We do not find any galaxy with a sharp (or complete)
cut-off in the radial light distribution. This means truncated
galaxies are in fact best described by a broken exponential with a
shallow inner and a steeper outer exponential region separated at a
more or less well defined break radius.
- 7.
- For Type II-CT galaxies the break happens already at
times the inner scalelength at a typical surface brightness
of
-mag/
. The position of
the break (in kpc) seems to be correlated with absolute
magnitude: the more luminous the larger the inner disk of the
galaxy.
- 8.
- For Type III galaxies the break happens typically further
out at
times the inner scalelength, and at a
lower surface brightness of
-mag/
.
For more than
of these galaxies we find good indication that the
outer upbending part is a disk-like structure (e.g. by finding
spiral arms). Close physical neighbours and slightly disturbed morphology
suggest in several cases interaction as a possible origin.
Acknowledgements
We would like to thank Peter Erwin and John Beckman for their
stimulating discussions and useful suggestions during this work
and especially Peter Erwin for helping with the ellipse task and
for carefully reading parts of this paper.
Thanks also to Reynier Peletier for reading the paper and for suggesting
to use the derivative method for objectively quantifying the break
radius. We also thank Marco Barden for very stimulating discussions
and we would like to thank the anonymous referee for detailed
comments which helped us to improve the quality of the manuscript.
Part of this work was supported by a Marie Curie Intra-European
Fellowship within the 6th European Community Framework Programme.
This research has made use the Lyon/Meudon Extragalactic Database
(LEDA, http://leda.univ-lyon1.fr) and the
NASA/IPAC Extragalactic Database (NED) which is operated by
the Jet Propulsion Laboratory,
California Institute of Technology, under contract with the National
Aeronautics and Space Administration.
This research has made use of NASA's Astrophysics Data
System Bibliographic Services.
Funding for the creation and distribution of the SDSS Archive has been
provided by the Alfred P. Sloan Foundation, the Participating Institutions,
the National Aeronautics and Space Administration, the National Science
Foundation, the US Department of Energy, the Japanese Monbukagakusho,
and the Max Planck Society. The SDSS Web site is
http://www.sdss.org/.
The SDSS is managed by the Astrophysical Research Consortium (ARC) for
the Participating Institutions. The Participating Institutions are The
University of Chicago, Fermilab, the Institute for Advanced Study, the
Japan Participation Group, The Johns Hopkins University, the Korean
Scientist Group, Los Alamos National Laboratory, the Max-Planck-Institute
for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA),
New Mexico State University, University of Pittsburgh, University of
Portsmouth, Princeton University, the United States Naval Observatory,
and the University of Washington.
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Online Material
Table 1:
Global parameters of the LEDA-SDSS DR2 subsample:
(1) principal name in LEDA,
(2) right ascension, and
(3) declination,
(4) RC3 de Vaucouleurs et al. (1991) Hubble-type, and
(5) LEDA Hubble-type,
(6) coded LEDA Hubble parameter T,
(7) absolute B band magnitude, corrected for
galactic plus internal extinction, and k-corrected,
(8) apparent diameter, defined by the isophote at the
brightness of 25 B-mag/
,
(9) heliocentric radial velocities corrected for the
Local Group infall onto Virgo,
(10) estimated distance according to the Hubble relation
with the Hubble constant of
km s-1 Mpc-1,
(11) weighted average of the measurements maximum rotation
velocity from radio (
I ) and optical rotation curves (H
).
Table 2:
Background (sky) and ellipse parameters:
(1) principal name in LEDA,
(2+6) photometric
and
band zero points,
(3+7) background value estimated around each galaxy,
(4+8)
of background from the ellipse method
(cf. Sect. 3.3),
(5+9) limiting surface brightness due to this background, used to
constrain the outer boundary of the exponential fits,
(10) radius used for fixing the ellipse parameters
(cf. Sect. 3.5),
(11) mean position angle PA (for
and
band) of
the fixed ellipse (as measured on the SDSS image),
(12) mean ellipticity ME (
and
band) of the fixed
ellipse.
Table 3:
Results: disk type and exponential disk parameters.
(1) Principal name in LEDA,
(2) profile classification (cf. Sect. 4.1),
(3) fitting boundaries for the inner and outer exponential
disk region,
(4) break radius in units of arcsec and kpc,
(5) inner scalelength in units of arcsec and kpc
(6) inner scalelength in relation to the outer scalelength,
(7) the central surface brightness of the inner/outer disk,
(8) the surface brightness at the break radius (estimated
at the crossing point of the two exponential fits),
(9) galactic extinction according to Schlegel et al. (1998).
For each galaxy two rows of values are given. The results obtained for
the
band in the upper row, for the
band in
the lower row. For galaxies with mixed classification both disk fits
are shown.
Appendix A: Galaxy atlas
The atlas presented here contain the 85 (from 98) galaxies
with useful images in the SDSS Second Data Release (DR2)
as described in Sect. 2.1.
The data for every two galaxies is presented on a single page.
On the left side we give detailed comments on the individual
galaxies concerning the applied classification and global
characteristics (such as distinct morphological features
or environment).
The headline gives the name and classification type. Below
we reproduce the main parameters: Position (J2000),
RC3 Hubble-type, coded LEDA Hubble parameter T,
absolute B band magnitude M
abs [B-mag],
apparent diameter ['], virgocentric radial velocity
v
vir [km s-1].
On the right side we reproduce the JPEG
colour mosaics
obtained with the SDSS "Finding Chart''
tool
.
Overlayed are a N-S, E-W grid through the center, a
scale
bar, and the outline of the individual SDSS fields.
In addition we show azimuthally averaged, radial surface
brightness profiles in the
(triangles) and
(circles) band obtained from fixed ellipse
fits.
The
-band is overlayed by the best exponential fits
(cf. Sect. 4.2) to the individual regions: single disk,
inner and outer disk, or three fits in the case of a mixed
classification.
The boundaries (b1-4) used for the fit are marked with
the short vertical, dashed lines on the abscissa.
Following Courteau (1996) we also chose not to show error
bars on all the profiles to avoid overcrowding of the plots.
Instead, we show for the
-band (horizontal,
dashed line) and for the
-band (horizontal,
dotted line) the critical surface brightness (
)
down to which the profile is reliable. This limit is placed where
profiles obtained by using
deviate by more than
0.2 mag from the one with our mean sky value (cf. Sect. 3.3).
In the upper right corner of the surface brightness profiles
we note the galaxy name, the Hubble type according to RC3
(for galaxies without or uncertain (S?) classification from LEDA),
and the profile type.
![\begin{figure}\par\includegraphics[width=5.7cm,angle=270]{4883f032.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f033.ps}
\par\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg232.gif) |
IC 1067: Type II.o-OLR (possible Type I)
J145305.2+031954 .SBS3. 3.0 -18.97 2.0 1665
Galaxy close to the border of the SDSS field but almost complete
with a nearby, physical companion (IC 1066, v=1577 km s-1 ) only
away, which slightly influences the background
estimation (together with two nearby bright stars).
The strong peak at
in the final profile is related
to the ring around the prominent bar and the dip at 35
to the inter-arm region of the two symmetric spiral arms peaking
at 40
.
Although possible to fit (at least for the
band profile) with
a single exponential (Type I), we classify the galaxy as Type II.o-OLR,
with a break around twice the bar radius at
,
having
an inner disk region too small to be detected with our automatic
break searching routine.
This is consistent with the classification and profile by
Erwin et al. (2006).
The region inside
is excluded for the fit
of the outer scalelength.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f034.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f035.ps}
\par\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg233.gif) |
IC 1125: Type I
J153305.6-013742 .S..8* 7.7 -20.05 1.7 2868
According to the coordinates in NED the companion (KPG 467A) in
Karachentsev's Isolated Pairs of Galaxies Catalogue Karachentsev (1972)
corresponds only to a faint starlike object about
away.
The small bump in the radial profile at 40
corresponds
to an outer spiral arms. Otherwise we see no obvious deviation from a
single exponential and therefore the galaxy is classified as Type I.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f036.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f037.ps}
\par\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg235.gif) |
IC 1158: Type II.o-CT
J160134.1+014228 .SXR5* 5.3 -19.36 2.2 2018
Galaxy shows clearly a truncated profile with an extended break region,
starting approximately at the end of the spiral arms. The center looks
like a secondary bar with a small ring embedded in larger bar of size
roughly
(without any noticeable feature in the
final profile). So the break with downbending profile at
is well beyond a typical Type II.o-OLR break.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f038.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f039.ps}
\par\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg236.gif) |
NGC 0450: Type II.o-CT
J011530.8-005138 .SXS6* 6.0 -19.63 3.0 1712
A background galaxy (UGC 00807, 11587km s-1 ) is superimposed. The mean
ellipticity of the outer disk is difficult to determine. The inner
disk looks fairly round whereas the outer disk looks rather elliptical.
The size of the slightly more elliptical inner part, associated
to be the bar (although without any noticeable feature in the
final profile), is roughly 8
,
so the break with
the downbending profile at 84
is well beyond a
typical Type II.o-OLR break and roughly outside the spiral arm region.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f040.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f041.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg237.gif) |
NGC 0701: Type II.i (possible Type I)
J015103.8-094209 .SBT5. 5.1 -19.74 2.5 1729
Galaxy is in a multiple system together with NGC 0681 and
NGC 4594 (where PGC 006667 (see below) is also part of) with an
additional small physical companion (IC 1738, v=1750 km s-1 )
about
away.
Galaxy close to our high axis ratio limit so the dust may have some
influence. The inner region shows no nucleus, so the centering
is done from the outer isophotes.
The extend of the bar is unknown, but the visible bump at
is probably not related to a bar. It is possible to construct a break
at
(which would be more pronounced in the
band),
but the inner drop could be also due to the higher inclination with dust
and/or patchy star formation affecting the profile.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f042.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f043.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg238.gif) |
NGC 0853: Type III
J021141.5-091817 .S..9P 8.3 -18.42 1.5 1405
The inner region shows no clear nucleus but many II regions, so the
centering is done from the outer isophotes. The inner disk is slightly
asymmetric with an additional light patch in the western part, therefore
mean ellipticity and PA difficult to fix. Almost continuously upbending
profile beyond the peak at 15
,
which includes all II regions,
getting flat at 42
.
The inner profile is rather curved and
not well approximated with a single exponential. The apparent outer
break at 100
is only due to the improper fixed ellipse fit
in the outer parts.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f044.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f045.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg239.gif) |
NGC 0941: Type II-CT
J022827.9-010906 .SXT5. 5.4 -19.02 2.5 1535
Galaxy shows only a very small, point-like nucleus and is in a small
group of galaxies (including NGC 936 and NGC 955). The small dip
at 40
is associated with the inner spiral arm region.
Although classified as SAB no real bar visible on image or in the
profile thus the downbending break is classified as Type II-CT.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f046.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f047.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg240.gif) |
NGC 1042: Type II-AB
J024023.9-082558 .SXT6. 6.1 -19.83 4.4 1264
A large scale gradient (from top to bottom) in the background of
the
and
band image is removed with a linear fit.
Only partly fitted since
1/3 of galaxy is beyond
SDSS field.
Galaxy shows an asymmetric (frayed) extension towards the
south-east and a sharper edge towards the north-west, which makes
it not really lopsided but looking rather like being affected by
moving in a dense IGM. The extended (frayed) spiral arms build the
outer disk, so ellipticity and PA very difficult to fix. The inner
bump in the profile at 90
is due to spiral arms. The
inner profile is below the inward extrapolation of the outer disk,
but due to the asymmetric shape of the disk we call this galaxy
only Type II-AB.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f048.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f049.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg241.gif) |
NGC 1068 M 77: Type II.o-OLR
J024240.8-000048 RSAT3. 3.0 -21.69 7.6 1068
Only partly fitted since
1/3 of galaxy is beyond the SDSS field.
Galaxy appears to have an inner disk, elongated into a bar-like structure
sitting in an outer disk with clearly different PA and with indication
for an additional outer ring at 200
.
According to
Erwin (2004) it is a double-barred galaxy with an inner bar
of size 15-20
and an outer bar which is very oval
(not very strong) and very large (extending out to < 100
;
as seen by e.g. Schinnerer et al. 2000). The galaxy looks in this
sense similar to NGC 5248 (Jogee et al. 2002).
This peculiar shape makes its very difficult to decide on a mean
ellipticity and PA of the outer disk from the photometry. The
position of the outer ring corresponds to the downbending break at
190
and is therefore roughly twice the bar radius.
This suggests the Type II.o-OLR classification, although the profile
looks at first glance more like a Type III with a break at
100
.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f050.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f051.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg242.gif) |
NGC 1084: Type III
J024559.7-073437 .SAS5. 5.1 -20.20 3.2 1299
A large scale gradient (from top to bottom) in the background of
the
band image is removed with a linear fit.
Slightly inclined galaxy sitting clearly in a more roundish outer
envelope, beyond which some stream-like remnants of a possible recent
interaction are visible. Small edge-on galaxy along the stream path
is confirmed to be only a background galaxy. According to SDSS
spectroscopy there is another object inside the disk
(RA: 02 46 00.3, Dec -07 34 17) with similar velocity and
associated to a visible light concentration.
The peculiar shape of the outer disk region makes it very difficult
to decide on a mean ellipticity and PA from the photometry. The
resulting profile inside the break at 90
is rather
curved towards the center with additional kinks ( 25
and 50
), so it is not clear what the galaxy might be
inside the Type III envelope.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f052.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f053.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg243.gif) |
NGC 1087: Type III
J024625.2-002955 .SXT5. 5.3 -20.46 3.7 1443
An apparent faint low surface brightness (center-less) structure
towards the North is only scattered light from a nearby star.
The galaxy center is not well defined, it shows only a small bar-like
structure with a double nucleus, so we used the slightly lopsided
(but symmetric) outer disk for centering, which accounts for the
central drop inside 50
in the final profile. There is
no spiral structure visible in the outer disk. The transition seems
to be rather sharp, but the inner profile is almost curved, so it is
not clear what its break type is inside the Type III envelope.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f054.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f055.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg244.gif) |
NGC 1299: Type III
J032009.4-061550 .SBT3? 3.2 -19.25 1.2 2197
Galaxy is small and close to our high axis ratio limit. The background
exhibits a gradient but the galaxy is small enough to avoid fitting it.
SDSS spectroscopy detects an object 0.2
away from center with
similar velocity. The rather symmetric outer disk shows no spiral
structure but has slightly different ellipticity and PA compared to
the inner part. The shoulder in the profile at 15
is related to the inner (bar-like) region with changing PA.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f056.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f057.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg245.gif) |
NGC 2541: Type II-CT
J081440.1+490341 .SAS6. 6.2 -18.50 5.8 734
Galaxy with low surface brightness disk, having many patchy SF
knots and an asymmetric (not well described with an ellipse),
lopsided outer disk, which makes the chosen ellipticity
and PA of the disk uncertain.
The central peak is off by
compared to the outer
disk where the centering is done, which causes the
dip in the final profile close to the center.
The downbending break at 140
is still inside the
nearly symmetric part of the disk, thus classified as Type II-CT but
this should be taken with some caution.
This galaxy was classified as SB in our original LEDA catalogue but
has been recently reclassified being now SAB. However, NED lists this
galaxy as SA, using the RC3 classification, which is consistent with
no bar being visible on the image or in the profile, so the downbending
break is not a Type II.o-OLR break.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f058.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f059.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg246.gif) |
NGC 2543: Type II.i
J081258.0+361516 .SBS3. 3.1 -20.66 2.5 2590
According to NED there is a dwarf elliptical galaxy (KUG 0809+363) at
a similar distance. On the SDSS image (confirmed with DSS) there is an
additional, low surface brightness structure visible at
RA 08 13 08.5 and DEC +36 16 35, which is possibly another
dwarf companion with an unknown distance.
The galaxy is clearly double barred with a
long
secondary bar. Two bright, s-shaped spiral arms dominate the inner
disk. The extended spiral arm towards the north-east is responsible
for a slightly asymmetric outer disk. This structure makes the
photometric measurement of the inclination (ellipticity) and PA
very difficult. The bar and pseudo-ring build by the inner spiral
arms are responsible for the prominent bump at 35
in
the profile, followed by a dip inside, which leads to the
Type II.i classification.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f060.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f061.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg247.gif) |
NGC 2684: Type II-CT
J085454.1+490937 .S?... 7.8 -19.76 1.0 3043
The rich cluster in background, with significantly redder colour, forces
a large background mask covering a small part of the galaxy. Slightly
asymmetric disk with bright center and no coherent spiral arms makes
ellipticity and PA uncertain. Bump at 12
in profile is
due to an inner ring-like structure, without an associated obvious bar
structure. The break at 25
is not related to a
morphological feature in the disk and, although at about twice the
ring radius, classified as Type II-CT.
The upbending profile starting at 42
is most probably
due to an improper sky subtraction caused by extended light from
the background cluster.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f062.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f063.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg248.gif) |
NGC 2701: Type II-AB + III
J085905.9+534616 .SXT5* 5.1 -20.36 2.1 2528
According to NED there is a small companion (with similar velocity)
superimposed on the galaxy disk towards the South at the end of
a spiral arm which is masked here in addition to the bright star on
the disk towards the West. The galaxy has a lopsided disk with the
bar being offcenterd compared to the outer isophotes, where the
centering is done. This is responsible for the dip in the center
an possibly for the break at 42
,
which is therefore
called Type II-AB.
The region beyond the second break at 70
corresponds to some
faint, almost symmetric light around the galaxy with some large extension
towards north-east, adding the classification Type III. This is possibly
triggered by interaction with the dwarf companion at the other side.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f064.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f065.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg249.gif) |
NGC 2776: Type I
J091214.3+445717 .SXT5. 5.1 -21.04 2.9 2796
The galaxy is classified as SAB but a bar is not obvious on the image.
The background estimate is uncertain due to a nearby (off-field),
extremely bright star. For the final profile we used a round ellipticity
instead of the usual value at
(cf. Sect. 3.5) which
gives an almost prototypical Type I profile with some minor wiggles,
a bump at
due to the inner spiral arms, and some outer
bumps due to some very weak spiral arm structures in the outer disk.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f066.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f067.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg250.gif) |
NGC 2967: Type III-d
J094203.3+002011 .SAS5. 4.8 -20.26 2.6 1858
The galaxy is close to the edge of the SDSS field in an area with an
increased background which is masked. Very faint, extended, but symmetric
spiral arms inside the outer disk at
are visible, which
do not continue inwards but start beyond the bump in the transition region
at 75
.
The exact break radius is therefore uncertain.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f068.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f069.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg251.gif) |
NGC 3055: Type II.o-CT
J095517.9+041611 .SXS5. 5.0 -19.90 2.1 1816
Galaxy is classified as SAB and shows a narrow, thin bar,
with the spiral arm structure wrapped around, which is responsible
for the bump in the final profile at 18
.
The break
with a downbending profile at 55
is well beyond a
typical Type II.o-OLR break.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f070.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f071.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg252.gif) |
NGC 3246: Type II-AB
J102641.8+035143 .SX.8. 8.0 -18.91 2.2 2138
Galaxy is selected from the NGC catalogue Tully (1988)
by (Pisano & Wilcots 1999) as being isolated. Their I measurements
show a lopsided disk which resembles the one on the present SDSS
image. The central bar region is clearly offcenterd compared to
the outer isophote, which is used for the centering. The downbending
break in the final profile and the downbending at the very center
is therefore most probably only an apparent break due to the fixed
ellipse fitting. Thus the galaxy is classified as Type II-AB.
The background is rather disturbed by a bright star,
but the galaxy is small enough not to be significantly influenced.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f072.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f073.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg253.gif) |
NGC 3259: Type III-d
J103234.8+650228 .SXT4* 4.0 -19.84 2.1 1929
The background is rather disturbed by a bright star, but the galaxy
is small enough not to be significantly influenced. Galaxy is isolated
according to Prada et al. (2003), but has one SDSS-detected dwarf companion
( 18.0
-mag) about 10
away with similar
velocity (v=1744 km s-1 ) and another possible, dwarf companion (or large
II region) projected on the south part of the disk (no counterpart in NED),
which is partly covered by a foreground star, but also clearly present on the
DSS image.
The break region of the upbending profile at
is
fairly extended and curved. The inner profile shows wiggles at
15
and 30
,
but the resolution is too
low to identify a bar or ring. The spiral structure apparently
extends into the outer disk well beyond the break, with two,
thin symmetric spiral arms (plus more fluffy ones) starting at
the defined break radius. However, it is not clear if they are
really the continuation of the inner arms.
The upbending characteristic is confirmed by a profile shown in
Courteau (1996) (see UGC 05717).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f074.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f075.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg254.gif) |
NGC 3310: Type III
J103845.8+533012 .SXR4P 4.0 -20.25 2.8 1208
The galaxy is clearly disturbed with a shell-like structure in the
outer disk, which is probably the result of a recent merger with a
smaller galaxy (cf. Conselice et al. 2000). The inner region is also
slightly asymmetric, but still used for centering. The inner region,
corresponding to a high surface brightness, tightly wound spiral, inside
the break at 50
,
is curved starting at 20
.
The wiggles in the outer disk are due to the shells. An additional
upbending beyond 150
is due to a prominent outer shell.
The very outer parts are in addition influenced by an inhomogeneous
sky and a large mask.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f076.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f077.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg256.gif) |
NGC 3359: Type II-AB
J104636.3+631328 .SBT5. 5.0 -20.42 7.2 1262
The inner disk shows an extended bar (roughly
), which
is not visible in the final profile, and two bright spiral arms.
The broad extension of this arms build the outer disk, so there
is no clear elliptical outer structure visible which makes the
photometric inclination (ellipticity) and PA measurements highly
uncertain.
The outer slope is influenced by a rather uncertain sky estimate
in both bands, but the apparent downbending break at 200
is not due to a sky error, but coincides with the region where the
two outer arms dominate. Thus the galaxy is classified as Type II-AB.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f078.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f079.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg257.gif) |
NGC 3423: Type II-CT
J105114.3+055024 .SAS6. 6.0 -19.54 3.9 1032
Bulge-like inner region (
30
)
coincides with inner high
surface brightness disk with spiral structure. Final profile is clearly
downbending but the exact break radius is difficult to place due to an
extended feature around 70
corresponding to an aligned spiral
arm (with a possible straight structural element towards the north-east,
called (Chernin 1999) spiral-arm row).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f080.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f081.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg259.gif) |
NGC 3488: Type II.o-CT
J110123.6+574039 .SBS5* 5.1 -18.80 1.6 3226
Galaxy is isolated according to Prada et al. (2003). A bright star
covering part of the outer disk needs an extended mask. A small bar
of roughly
size is visible as an elongated isophote
on the image. The final profile is clearly downbending, but the exact
break radius is difficult to place. The extended break region resembles
in this case again a straight line, thus one could also define two
break radii at 32
and 58
.
This could
be caused by the extended mask, whereas the spiral structure extending
to 40
seems not to be responsible for this behaviour.
The bar is to small for its OLR to be associated with the first break,
thus the galaxy is classified Type II.o-CT. The light beyond
58
is still symmetric and not affected by sky errors.
The peak at 20
corresponds to the inner two arms.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f082.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f083.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg260.gif) |
NGC 3583: Type III-d
J111411.0+481906 .SBS3. 3.2 -19.57 2.3 2347
The apparent companion, a spiral galaxy (NGC 3577) towards the
south-west is non-physical with v=5336 km s-1 . The galaxy shows a
stream-like arm extending towards the north-west outside of the
galaxy connected to a small superimposed E0 satellite at
north (not in NED). Due to this structure the outer disk seems to
have a slightly different ellipticity and PA. The bump at 30
in the final profile is due to the end of the bar and beginning of
spiral arms. The inner profile with an extended wiggle at 55
(corresponding to the spiral arms) makes it difficult to characterise the
break region (starting at 85
with an upbending profile) as
being curved or sharp.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f084.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f085.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg261.gif) |
NGC 3589: Type II-CT
J111513.2+604201 .S..7* 7.0 -18.49 1.5 2217
Due to the higher inclination and extended elongated structure the size
of the bar is not well defined. The center is also not well defined, but
centering on the outer isophote coincides roughly with the brightest pixel.
The sky estimate is rather uncertain due to the bright star in the FOV.
The final profile shows a downbending break at 40
,
classified
as Type II-CT but also consistent with being Type II.o-OLR allowing the bar
to be of size 20
which is consistent with the image.
The small bump 22
in the profile just corresponds to
some aligned II regions.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f086.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f087.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg263.gif) |
NGC 3631: Type I
J112102.4+531008 .SAS5. 5.1 -20.62 4.9 1388
The galaxy forms a nearby group together with NGC 3178, NGC 3898,
NGC 3953 and NGC 3992 (also part of our sample) in the Ursa Major
cluster and shows plenty of substructure.
It has two prominent spiral arms with different pitch angles, one
of them turns nearly straight, classified by Arp (1966) as a
spiral galaxy with one heavy arm.
In addition, it has a faint extended spiral arm
(or maybe stream-like structure) in the far outer disk towards North,
therefore the outer disk is slightly asymmetric and the mean ellipticity
and PA are difficult to fix. There is an extended light patch on the
image visible towards south-west. Although there is no bright star
nearby which could create such an artefact it is unlikely a dwarf
companion, since it is not visible on the DSS.
The final radial light profile is quite unusual and cumbersome to
classify, since it exhibits an extended bump between
50-140
,
which corresponds to the begin of the two
spirals to the end of the inner (undisturbed) disk.
Beyond 140
the extended, slightly offcenterd outer
disk with the spiral arm structure (or stream) starts.
If we do not exclude the bump from the fit, one can argue for a
downbending break at 75
,
or a Type I profile with
an extreme wiggle (this would be a Type II.i if the galaxy would
be barred). We decided to exclude the bump and the inner region
from the fit (
)
which gives also a Type I
profile where the region around 35
is also roughly
fitted.
Due to this problems the classification should be taken with caution.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f088.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f089.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg264.gif) |
NGC 3642: Type III-d
J112218.0+590427 .SAR4* 4.0 -20.60 5.5 1831
The background is slightly inhomogeneous and the galaxy is rather
extended. From the nearly round inner disk a single, star forming,
spiral arm starts towards the outer disk with slightly more than one
revolution, forming the strongly asymmetric, lopsided outer disk.
Therefore the ellipticity and PA is determined further inside.
The final profile looks fairly curved and with extended wiggles
in the outer disk at 100
and 155
due to the outer spiral arm passing the ellipse.
There is a steeper inner exponential part visible between
25-75
followed outwards by an upbending profile,
which is roughly at the position where the extended spiral arm
starts to unwrap, which leads to the Type III classification.
Inwards of 25
there is again another steeper
exponential part visible together with a possible bulge
component.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f090.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f091.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg266.gif) |
NGC 3756: Type II.o-CT
J113648.3+541737 .SXT4. 4.3 -19.89 3.8 1525
Only partly fitted since
1/4 of galaxy is beyond field.
Known three armed spiral galaxy which shows one wide spiral arm
starting at 60
extending roughly towards the downbending
break at 100
.
The extended bump 45
is due
to the three inner tightly wound spiral arms and makes it, similar to
NGC 3631, difficult to fit the inner region. However, since the bump is
less strong we decided to include it. The galaxy is classified as SAB
(RC3) but the bar is not obvious on the image and its maximum
size would be
thus the break is well outside the
range for typical Type II.o-OLR breaks and is classified as Type II.o-CT.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f092.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f093.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg267.gif) |
NGC 3888: Type I
J114734.7+555800 .SXT5. 5.3 -20.43 1.8 2648
The background on the image shows a large gradient due to a bright star
off the field, but the galaxy is small enough to be not affected.
The galaxy has one "malformed'' (kinked) spiral arm across the disk.
There is a possible dwarf, irregular companion visible towards the
south-west, but without any distance information.
The final profile exhibits an extended wiggle (with an unusual integral
sign shape) at 33
,
looking like two shifted exponential
regions, but there is no point in placing a break there.
The peak at 22
is related to an aligned spiral arm,
whereas the peak at 12
could be due to the end of a
possible bar or inner ring (no obvious on the image).
Therefore the galaxy is classified as Type I and not as
Type II.i, although the dip in the profile is clearly visible. It
could be explained by dust lanes close to the center, which also
explains the dip being more prominent in the
band.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f094.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f095.ps}\par
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg268.gif) |
NGC 3893: Type III-d
J114838.4+484234 .SXT5* 4.8 -20.33 4.1 1193
The background around the galaxy is affected by a nearby, bright star
and a close (3.7
away, with similar velocity v=905 km s-1 ,
SB0/a:pec), smaller, companion galaxy (NGC 3896), both members of
the Ursa Major Cluster.
Galaxy exhibits a wide, extended spiral arm like structure towards
the east, which could also be a stream or tidal feature.
Due to this structure it is not possible to derive the ellipticity
and PA from the outer disk, so their values are more uncertain.
The final profile clearly shows an Type III upbending profile
starting at 150
corresponding to the beginning
of the extended structure to one side and some more symmetric
faint light on the other side. The inner disk shows a prominent
wiggle 90
which is associated to a pseudoring of
wrapped spiral arms.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f096.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f097.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg270.gif) |
NGC 3982: Type III
J115628.3+550729 .SXR3* 3.2 -19.54 2.3 1351
Close to Ursa Major Cluster but membership questionable
(Tully et al. 1996). Galaxy exhibits a detached, narrow, starforming
spiral arm embedded into the very outer, symmetric disk towards
south-west.
The final profile beyond the central part is smooth and straight down
to 55
where it clearly starts upbending, classified
as Type III, which is consistent with the profile by (Tully et al. 1996).
The break corresponds to the end of the inner disk, excluding the
faint outer arm, which produces the bump at 75
(more
pronounced in the
band). The transition zone is rather sharp.
Dip-peak structure between 5-12
corresponds to the inner
bar/ring region. The exact size of the bar is not well determined
on the SDSS image. Erwin (2005), using HST images, gives 5
and classifies the galaxy therefore as Type II.o-OLR + III (with an "extreme''
OLR break). We exclude the inner
from our fit
and leave it with a Type III classification.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f098.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f099.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg271.gif) |
NGC 3992 M 109: Type II.o-OLR
J115735.9+532235 .SBT4. 3.8 -20.98 6.9 1286
Large galaxy with a small part off the SDSS field. Member of Ursa
Major Cluster (Tully et al. 1996). Embedded in the large bar of size
roughly
(as measured on the image) is possibly a
secondary bar half the size.
Unusual very faint extension visible in both bands (more pronounced
in
band) towards north-east, which is possibly but unlikely
stray-light from a nearby bright, red star. The one-sigma ellipse
is therefore not representative so the mean ellipticity and PA
are determined further inside.
Final profile shows a clear downbending break at 140
at about twice the bar radius corresponding roughly to a pseudoring
of the spiral arms, therefore classified as Type II.o-OLR.
Bump at 200
does not coincide with a spiral arm.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f100.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f101.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg273.gif) |
NGC 4030: Type III
J120023.4-010603 .SAS4. 4.1 -20.27 3.9 1476
Two superimposed bright stars are masked. According to Zaritsky et al. (1993)
it is an isolated galaxy with a satellite system (largest UGC 06970,
SB(s)m, with
). The galaxy shows two prominent spiral
arms beyond a more flocculent center starting at 30
,
followed by a single arm extending slightly further out towards
south-west.
Final profile shows a Type III break at 150
where the transition
zone is rather sharp, followed by a fairly symmetric outer region without
spiral structure. The bump at 80
corresponds to the end of
inner spiral arms.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f102.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f103.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg274.gif) |
NGC 4041: Type III-d
J120212.2+620814 .SAT4* 4.3 -19.92 2.7 1486
According to Sandage & Bedke (1994) this galaxy forms a kinematic triplet
with NGC 4036 and UGC 7009 and is probably member of the Ursa Major
Cluster. However, Tully et al. (1996) does not list any of these as members.
Galaxy shows a detached, extended, star-forming spiral arm structure in
the outer, asymmetric disk, similar to NGC 2967, but smaller and only
one-sided, which makes the photometric inclination (ellipticity) and
PA uncertain.
In the final profile the disk inside the Type III break at 75
corresponds roughly to the region with the spiral arms, which are also
responsible for the extended bump between 30-75
(more
pronounced in
band).
The very inner region looks bar-like, but is probably only the spiral
structure continuing into the center.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f104.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f105.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg276.gif) |
NGC 4102: Type II.o-OLR + III
J120623.1+524239 .SXS3$ 3.0 -19.38 3.1 1082
Galaxy belongs to the Ursa Major Cluster Tully et al. (1996).
On the image an elongated inner bar region inside a starforming
ring is visible which is responsible for the dip and bump structure
between 25-35
in the final profile. Erwin (2005)
measures the size of the bar to 15
and the outer ring
to 35
,
so the apparent break at
(although measured from outside, it starts only at 58
)
is classified as a Type II.o-OLR. The apparent upbending at 120
is unlikely a sky error, visible around the whole galaxy and
confirmed by the profile in Courteau (1996) (see UGC 07096)
and also visible in Erwin et al. (2006). This adds the Type III
classification.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f106.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f107.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg277.gif) |
NGC 4108: Type II-AB
J120644.0+670944 PSA.5* 5.0 -20.13 1.7 2828
Galaxy in a triple system with NGC 4108A (v=2256 km s-1 ) and
NGC 4108B (v=2673 km s-1 ), the latter is also part of the present
sample. According to Nordgren et al. (1997) NGC 4108 and NGC 4108B
appear to be possibly joined by an I bridge.
Very inner center
looks like small bar, or the
spiral structure starts from the very center.
The outer disk is asymmetric with one side rather sharp and the
other more shallow with indication for a single spiral arm. The
disk is lopsided, so the outer contour is used for centering
(center 4
off the brightest pixel, causing the
central dip in the profile), which implies that the photometric
inclination (ellipticity) and PA are not well defined.
The apparent break at 44
is related to the transition
between the symmetric outer disk going inwards to the offcenterd
inner disk and therefore most probably not intrinsic but a Type II-AB
break.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f108.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f109.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg278.gif) |
NGC 4108B: Type I
J120711.3+671410 .SXS7P 7.0 -18.46 1.3 2840
Companion to NGC 4108 (see above). Galaxy exhibits an offcentered
bar ( 5
off compared to the center derived from the
outer isophote). Very outer disk slightly asymmetric towards
north-east (outer spiral arm?). In the final profile the central
dip and inner wiggle are due to the the offcentered bar, the peak
at 22
corresponds to an aligned spiral arm-like
region. Although a downbending break at 32
with low
scalelength contrast is possible, Type II-AB, the galaxy is consistent
and classified as Type I due to the wiggles in the center.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f110.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f111.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg280.gif) |
NGC 4123: Type I
J120811.1+025242 .SBR5. 4.8 -19.55 4.1 1364
Galaxy with extended bar (
)
studied in detail
by Weiner et al. (2001) using a surface brightness profile which is
consistent with the SDSS one.
The outer disk is slightly asymmetric, more rectangular than
elliptical, with an extended starforming spiral arm structure
towards south-west, which makes the photometric inclination
(ellipticity) and PA uncertain.
The final profile exhibits extended wiggles. The bar and associated
spiral arms are visible between 30-110
and the bump
at 170
corresponds to a starforming outer spiral arm.
Although being far from a prototypical Type I we used this
classification, since the profile shows too many changes to
reasonably argue for any other type.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f112.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f113.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg281.gif) |
NGC 4210: Type II.o-OLR + II.o-CT
J121515.9+655908 .SBR3. 3.0 -19.89 2.0 3000
Companion galaxy (CGCG 315-030, m=15.5) 13
away with similar
velocity (v=2679 km s-1 ). Gradient in the background due to a very
bright star (off field), but galaxy small enough to be not significantly
influenced.
The final profile shows an inner bump at 15
corresponding
to a pseudoring of wrapped spiral arms (slightly further out than the bar).
The apparent dip 8
is due to the bar orientation being
perpendicular to the major axis of the galaxy.
Similar to NGC 3488 the profile shows a clear downbending. However,
the break radius is uncertain due to the extended break region, which
resembles in this case again a straight line. Thus one could also
define two break radii at 33
,
corresponding roughly to
end of inner spiral arm structure, and 55
,
not related
to sky errors and symmetric around the disk.
In contrast to NGC 3488 the bar is here large enough to argue for
a combination of a Type II.o-OLR and a Type II.o-CT break, this should be
confirmed with a more detailed study on the bar size of NGC 4210.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f114.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f115.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg282.gif) |
NGC 4273: Type II-AB + III
J121956.2+052036 .SBS5. 5.1 -20.41 2.1 2435
Galaxy in south-western corner of the Virgo Cluster with three
similar sized neighbours, NGC 4268, NGC 4281, and closest
and slightly overlapping at the very outer disk NGC 4277.
The disk is lopsided with one side sharp edged and the other side
with a wide spiral arm feature towards south-east (embedded in
the outer disk), similar to NGC 4108. Centering on the outer
disk causes the dip at 10
and hides the very bright
nucleus sitting in a bar-like structure which is offcentered
by 16
.
The break at 45
in the final profile is clearly
related to the lopsided disk and therefore classified as Type II-AB.
In addition, there is an Type III break with an upbending profile
visible beyond 80
due to the influence of the
companion (possibly intrinsic and not just projected).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f116.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f117.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg284.gif) |
NGC 4480: Type II.o-CT
J123026.8+041447 .SXS5. 5.1 -20.14 2.1 2494
The galaxy is small, rather inclined, and classified as SAB with
bar size of roughly
(measured from the image).
The final profile shows a clear downbending break at
55
,
significantly further out compared to a
typical Type II.o-OLR break thus classified as Type II.o-CT, corresponding
roughly to the end of the spiral arms. The inner profile exhibits
an extended bump at 35
(more pronounced in the
and less in the
band) most probably related to the star formation
in the spiral arms and not to a possible Type II.o-OLR + II.o-CT as for NGC 4210,
which shows the same structure in both bands.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f118.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f119.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg286.gif) |
NGC 4517A: Type II.o-CT + II.o-AB
J123228.1+002325 .SBT8* 7.9 -19.18 3.8 1562
This low surface brightness galaxy has an elongated, barred center,
of size
,
with a foreground star very close and
a slightly asymmetric, lopsided outer disk.
The final profile exhibits a sharp break at 150
due to the asymmetric outer disk, which is not well described
with the mean ellipticity and PA used, thus classified as Type II-AB.
There is an additional feature (bump or break) visible around
80
,
which is not obviously related to an aligned
spiral arm and could be explained by a weak downbending break.
Since the bar appears to be only weak and the break at more
than twice the bar radius it is classified as Type II.o-CT, which
should be taken with caution.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f120.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f121.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg287.gif) |
NGC 4545: Type II.o-CT
J123434.2+633130 .SBS6* 5.9 -20.49 2.5 3000
Small galaxy with an s-shaped inner region of size 12
(associated to be the bar) leading to two (or three) tightly wrapped,
spiral arms.
Final profile exhibits a break at 58
,
being too far
out for a typical Type II.o-OLR thus classified as Type II.o-CT.
The dip at 8
corresponds to the region where the spiral
arms start from the bar-structure which is nearly perpendicular to the
ellipse major axis.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f122.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f123.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg288.gif) |
NGC 4653: Type II-AB
J124350.9-003341 .SXT6. 6.1 -20.37 3.0 2658
Paired galaxy with NGC 4642 (v=2471 km s-1 , 10
away)
while apparent dwarf companion on the image towards south-east
is a confirmed background galaxy (v=7843 km s-1 ).
Extended mask used to avoid straylight by bright stars.
Mean ellipticity and PA difficult to determine, since it is
different for the inner disk (used for centering) with two,
very regular spiral arms inside
30
,
compared to
the outer disk with more frayed spiral fragments, starting to be
asymmetric on larger scales at
(mainly towards
south-west). This asymmetry causes also the apparent break at
105
thus the galaxy is classified as Type II-AB.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f124.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f125.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg289.gif) |
NGC 4668: Type III
J124532.0-003209 .SBS7* 7.1 -18.88 1.5 1654
Small galaxy close to our high axis ratio limit, which forms a close pair
with NGC 4666 (v=1474 km s-1 ) about
away and also has a wider
association with NGC 4632 (v=1557 km s-1 ) according to Sandage & Bedke (1994).
The final profile exhibits a break at 70
followed
by an upbending profile corresponding to a slightly asymmetric,
faint outer disk and although close to, most probably not related
to a sky error, thus classified as Type III.
The full extend of the bar is uncertain, although the bump around
20
is certainly related to the bar and a possible
spiral arm. The whole inner region is included in the inner
disk fit.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f126.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f127.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg291.gif) |
NGC 4904: Type II.o-OLR + III
J130058.6-000138 .SBS6. 5.7 -18.69 2.1 1213
Only partly fitted since
1/5 of galaxy is beyond field.
The galaxy has a dominating, thick bar of size
whereas the center along the bar is not well defined (centering
on brightest pixel). It has an unusual spiral arm structure
with one extending nearly straight towards south-west forming
more droplet shaped isophotes.
The image shows indication for an additional, extremely faint,
extended patch of light outside the disk towards south-west.
Final profile shows a clear downbending break at 40
,
associated on one side with a ring-like structure which is about
twice the bar radius, thus classified as Type II.o-OLR.
The apparent upbending at 90
is almost certainly
produced by the additional patch of light unrelated to any
artificial source, thus adding the Type III classification.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f128.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f129.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg293.gif) |
NGC 5147: Type II.o-OLR + III
J132619.2+020604 .SBS8. 7.9 -18.77 1.8 1154
The medium-sized star superimposed on the galaxy close to its
center is masked. The bar size is uncertain but could be associated
to an elliptical region of size
on the image not
reflected in the final profile.
The extended bump between 25-45
is associated
to the inner disk containing the spiral arms with some
ring-like, distributed SF regions. Excluding the full
region allows for a crude Type I classification.
However, using a break at 30
(about twice
the bar radius thus classified as Type II.o-OLR) followed by a downbending
profile with another break at 75
leading to an upbending
profile (therefore classified as Type III) seems more reasonable,
even so the upbending is very close to our detection limit.
The disk beyond the ring-like structure is slightly asymmetric with
a single, wide, and faint spiral arm-like structure towards north-east
just inside the outer break. The outermost isophote is again
nearly round and symmetric.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f130.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f131.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg295.gif) |
NGC 5300: Type II.o-CT
J134816.1+035703 .SXR5. 5.0 -18.93 3.5 1246
Galaxy close to border of SDSS field but almost complete. The size
of the weak bar is about
(measured from the image).
The final profile shows the prototypical Type II.o-CT behaviour. A sharp
break at 85
followed by a downbending profile. The break
is way to far out for a normal Type II.o-OLR break given the small bar
size, and corresponds roughly to the end of the visible spiral
arm structure.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f132.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f133.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg298.gif) |
NGC 5334: Type II.o-CT
J135254.4-010651 .SBT5* 5.0 -19.22 3.9 1433
Galaxy has a bar with a visible dust lane of size
as measured from the image.
The final profile is clearly downbending, but the exact position of
the break is difficult to place. The extended break region resembles
in this case again a straight line, so that one could also define two
break radii at 85
and 125
.
However, since
the first one is not even close to twice the bar radius and no other
particular feature is responsible for the second break, the galaxy
is classified Type II.o-CT with a single break at
.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f134.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f135.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg299.gif) |
NGC 5376: Type II.o-OLR
J135516.1+593024 .SXR3$ 3.0 -20.00 2.1 2293
Galaxy close to the border of the SDSS field but almost complete.
It has a known, similar-sized companion (UGC 08859, v=1610 km s-1 )
about
away and there is another possible, much
fainter dwarf companion (
away towards north-west)
visible on the image.
The final profile shows a weak break at 35
coinciding
with the end of some very faint spiral arms. The dip at 14
and the peak at
are related to a pseudoring structure
(mentioned also in RC1) around a possible bar. Although the exact size of
the bar is difficult to fix, assuming it is there, the break is close to
twice the inner ring radius and therefore classified as Type II.o-OLR.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f136.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f137.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg301.gif) |
NGC 5430: Type II.o-OLR
J140045.8+591943 .SBS3. 3.1 -20.86 2.2 3238
Galaxy is isolated according to Prada et al. (2003). The center is
dominated by a strong bar with dustlanes of size
,
followed by two wrapped spiral arms.
The very center is slightly elongated, looking twofold (effect of
dust lane?), thus the centering is uncertain.
The extended bump at 45
in the final profile
is associated with the wrapped spiral arms. We have included
the bump and bar for fitting the inner scalelength, because it
does not change the result much.
It is in principle possible to fit the full profile with a single
exponential (Type I), allowing for this extended bump. However, we
chose to fit a break at 70
.
This reduces the
deviation from the model and since it is about twice the bar radius
the galaxy is classified as Type II.o-OLR.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f138.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f139.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg304.gif) |
NGC 5480: Type III-d
J140621.5+504332 .SAS5* 5.0 -19.72 1.7 2119
A large scale gradient (from top to bottom) in the background of
the
band image is removed with a linear fit.
Galaxy forms a close pair with NGC 5481 (v=2143 km s-1 ) only
away with the very outer isophotes starting to
overlap.
Galaxy appears to consist of two regions. An inner disk with
the bright center and the spiral arms of size
with a common ellipticity and PA, sitting in a more diffuse outer
disk having a different ellipticity and a nearly orthogonal PA.
The systems looks like an extended bar in an underlying disk,
similar to NGC 1068 and the photometric inclination (ellipticity)
and PA is difficult to determine and therefore uncertain.
The final profile exhibits a break with an upbending profile at
,
thus classified as Type III, which is consistent
with the profile shown by Courteau (1996) (cf. UGC 09026).
Between the inner disk and the break there is indication for two
symmetric, thick spiral arms emerging from the inner bar-like disk.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f140.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f141.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg306.gif) |
NGC 5584: Type II.o-CT
J142223.8-002315 .SXT6. 6.1 -19.80 3.2 1702
Bright foreground star nearby but the influence is small. Two
additional brighter stars in the outer disk force extended masking.
The inner disk is dominated by two prominent spiral arms plus some
more asymmetric ones with many starforming patches.
The galaxy is classified as SAB, but the bar size (
)
is difficult to determine, since the spiral arms seem to continue
towards the center.
Similar to NGC 3488 the profile shows a clear downbending, however,
with uncertain break radius due to the extended break region which
resembles in this case again a nearly straight line, so that one could
also define two break radii at 60
and 110
.
Since the bar is too small to be responsible for the inner break
we use a single break at 90
enclosing roughly the
inner spiral structure followed by a slightly asymmetric outer
disk (one side with a clearly more diffuse appearance).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f142.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f143.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg307.gif) |
NGC 5624: Type III
J142635.3+513503 .S?... 5.0 -18.69 1.1 2186
Large scale gradient (from top to bottom) in the background of
the
band image is removed with a linear fit.
Very small galaxy which is most probably of noticeably later
type than classified (Sc).
Inner region dominated by an offcenterd (compared to the outer
isophote used for centering) narrow bar, or rim-like structure of
size 10
which is responsible for the central dip
in the profile.
The PA of the outermost region is twisted compared to the inner,
bar-like structure.
The final profile exhibits a straight line starting from
20
(enclosing the central region including the
bar having the same PA) down to a break at 45 followed
by an upbending profile (classified as Type III) into the more
symmetric, diffuse outer disk without visible substructure.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f144.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f145.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg310.gif) |
NGC 5660: Type II-CT
J142949.8+493722 .SXT5. 5.1 -20.62 2.8 2585
Galaxy close to the edge of the SDSS field but almost complete
sitting in a strip with higher background.
According to Sandage & Bedke (1994) it has a small companion nearby
("a likely dwarf Im companion of unknown redshift"), however this
could be associated with UGC 09325 (v=3730 km s-1 ) being clearly
a background galaxy.
Galaxy shows two, slightly asymmetric inner spiral arms plus
an additional one extending towards the outer disk. Although
classified as SAB there is no bar-like structure visible except
for a possible ring-like structure of size
.
The final profile is not well described with a single exponential
(Type I), already excluding the region beyond
which is most probably affected by an incorrect sky subtraction.
Unaffected of this it is better described as having a break
at 70
,
corresponding to the end of the single extended
spiral arm, with a following downbending profile, which is too far
out to be related to the possible bar and therefore classified
as Type II-CT.
The bump at 40
is related to the end of the inner
spiral arms and beginning of the outer extended one.
NIR imaging of the underlying old disk population should give
clarification to the classification.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f146.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f147.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg313.gif) |
NGC 5667: Type II.i + III
J143022.9+592811 .S..6* 5.8 -19.69 1.7 2222
Galaxy small and close to the edge of the SDSS field but almost
complete with an untypical appearance. The inner region
(
)
looks like an extended bar with dustlanes
and a possible additional, tilted, secondary inner bar of size
.
Outside this region there are two asymmetric
narrow spiral arms visible towards north-west followed by an
outer, slightly asymmetric, envelope, which makes the photometric
inclination (ellipticity) and PA uncertain.
The final profile shows a downbending break at 25
,
related to (and inside) the extended bar structure, therefore
classified as Type II.i, followed by an exponential down to another
break at 65
where an additional upbending starts
adding the Type III classification.
The outer profile is uncertain due to a higher error in the sky.
A still justifiable sky value could create a continuous outer slope,
but this is unlikely, since it will not create the asymmetric shape
of the outer isophotes.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f148.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f149.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg315.gif) |
NGC 5668: Type I
J143324.4+042702 .SAS7. 6.7 -19.65 2.8 1672
Galaxy close to the edge of the SDSS field but almost complete.
Although classified as SA there is a weak bar or oval inner
structure of size
visible on the image, reflected
by a small shoulder in the final profile.
The outer disk (beyond
)
is slightly asymmetric
and more extended towards the North.
The bump at 70
in the final profile is related
to brighter spiral arms in this region.
There is a possible upbending break visible at 100
(associated to the asymmetric outer disk) or 140
but the scalelength contrast is too low and it is too close to
the sky error to argue for a Type III classification.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f150.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f151.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg317.gif) |
NGC 5693: Type II-AB
J143611.2+483504 .SBT7. 6.8 -18.64 1.9 2537
Small galaxy with unusual appearance, showing an inner extended
bar-like structure of size
,
apparently with two
central peaks, probably caused by a superimposed foreground star.
The brightest pixel in the bar structure does not correspond to
the center obtained from the outer isophotes and is off by
causing the inner dip in the final profile.
The bar-like structure is followed by a single spiral arm extending
towards the outer (quite roundish and symmetric) disk, which is used
to obtain the ellipticity and PA.
The final profile cannot be well fitted with a single exponential
(Type I) but rather shows a downbending behaviour albeit with an
uncertain break radius due to the extended break region which
resembles again a nearly straight line, so that one could also
define two break radii at 30
and 50
.
Although the first break is at twice the bar radius, we classify this
galaxy as Type II-AB since this whole region is clearly lopsided with
an significantly offcentered bar.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f152.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f153.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg319.gif) |
NGC 5713: Type III
J144011.4-001725 .SXT4P 4.1 -20.50 2.8 1958
According to Sandage & Bedke (1994) in a group of late-type spirals
with four members in a region smaller than the Local Group.
No bright nucleus in the bar-like structure so the centering
is done from the outer isophotes.
In addition to a more chaotic inner region with spiral structure
(producing the bump between
in the final
profile) there is clear substructure in the outer disk visible.
Towards the South (
from the center) we see a very
diffuse additional patch of light (size
and
masked), in addition to a more elongated feature (
from the center, unmasked) towards north-east.
The profile shows a break at 115
with an upbending
profile associated with a rather symmetric featureless outer part.
The break is not caused by a possible sky error thus classified
as Type III.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f154.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f155.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg320.gif) |
NGC 5768: Type I
J145207.9-023147 .SAT5* 5.0 -19.24 1.6 2018
Bright star superimposed so using an extended mask.
Photometric inclination (ellipticity) at
in the free ellipse
fit does not match the outer parts well, therefore we used the outermost
ellipse which leaves the ellipticity and PA uncertain.
Similar to NGC 3888 the final profile exhibits an extended wiggle
(with an unusual integral sign shape) at 50
(without
being a break) corresponding to a set of spiral arms in the outer
disk which do not start at the center.
The inner break at 18
is associated with the inner
spiral arms and the bar-like center.
Although showing extended wiggles the galaxy is classified as
Type I since there is no better fitting alternative.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f156.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f157.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg322.gif) |
NGC 5774: Type II.o-OLR + III
J145342.6+033500 .SXT7. 6.9 -19.09 2.8 1655
Galaxy has a close physical, edge-on, companion (NGC 5775, SBc?,
v=1681 km s-1 ) and exhibits an outer, extended spiral arm pointing
towards NGC 5775 (similar to the M 51/NGC 5159 system but having
a more similar sized mass) producing an asymmetric outer disk where
the very outer isophotes already overlap.
The center is obtained from outer ellipse fits (different from
brightest pixel) since the inner elongated, narrow, bar-like
region
is without an obvious nucleus.
The shoulder in the final profile at
corresponds
to the end of the more extended bar-like structure enclosing the
inner bar having a different PA.
The break at 80
with the downbending profile being
at about twice the extended bar radius is therefore classified
Type II.o-OLR.
The upbending profile (classified as Type III) beyond a break at
120
is due to the asymmetric outer disk with
extended spiral arms.
Fitting the profile with a single exponential (Type I) leaves
three extended wiggles which are better explained by a
Type II.o-OLR + III break combination.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f158.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f159.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg323.gif) |
NGC 5806: Type III
J150000.4+015329 .SXS3. 3.3 -19.74 3.0 1440
Galaxy close to our high axis ratio limit (dust lane visible?) and
close to the edge of the SDSS field but almost complete.
From the inner disk there is an additional patch of diffuse light
visible towards the south-east (not masked) extending into the
asymmetric outer disk, which makes the photometric inclination
(ellipticity) and PA uncertain since obtained further in.
The final profile shows a shoulder at 40
related to
the inner bar-like center with the beginning of the spiral arms
and a break at 120
.
The break is close to the
position of the extra patch of light followed by an upbending
profile (classified as Type III) extending into the outer asymmetric
disk without spiral structure.
Our classification agrees well with Erwin et al. (2006) and the
Type III profile is also visible in Courteau (1996)
(cf. UGC 09645).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f160.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f161.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg327.gif) |
NGC 5850: Type II.o-OLR
J150707.7+013240 .SBR3. 3.0 -21.43 4.3 2637
Bright star nearby needs extended mask. The
band background
is slightly inhomogeneous.
Galaxy is dominated by an extended bar of size
enclosed by an inner ring out to
having a
secondary, inner bar of size
with clearly
different ellipticity and PA.
There is an additional, faint outer ring (or pseudo-ring, since
looking similar to some wrapped spiral arms) visible on the image
related to the break at 130
in the final profile,
thus obviously classified as Type II.o-OLR. Since the outer ring is
used to determine the photometric inclination (ellipticity) and
PA they are rather uncertain.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f162.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f163.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg328.gif) |
NGC 5937: Type III
J153046.1-024946 PSXT3P 3.2 -20.90 1.9 2870
Bright stars nearby need extended mask without really covering
the outer disk.
There is a possible, small dwarf companion (not in NED) visible
about
away towards the north-west.
The outer disk is slightly asymmetric with continuously changing
ellipticity and PA, so the values applied for the final
profile are rather uncertain.
The break at 70
with an upbending profile (classified
as Type III) is most probably related to the changing ellipticity
and should be taken with caution.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f164.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f165.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg330.gif) |
NGC 6070: Type II.o-CT
J160958.9+004234 .SAS6. 6.0 -21.04 3.4 2085
Galaxy close to our high axis ratio limit having a very bright star
(with an extended halo) in the FOV which is still small enough to
avoid significant influence. Only partly fitted since < 1/5
of galaxy is beyond SDSS field.
The outer isophotes are slightly asymmetric, with one sharp and one
more fluffy side, so the ellipticity and PA are uncertain.
The final profile exhibits a clear downbending with a more extended
break region around
corresponding to the end of
the spiral arm structure and classified as Type II.o-CT.
Although the galaxy is classified as SA there is an elliptical central
bar-like structure of size
visible which would be
however too small to argue for a Type II.o-OLR break.
The small dip at 30
is produced by spiral arm
contrast.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f166.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f167.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg332.gif) |
NGC 6155: Type II-AB
J162608.3+482201 .S?... 7.8 -19.45 1.3 2684
Small galaxy with an extended mask reaching into the outer disk
to cover a very bright star close by.
Lopsided disk with centering done from the outer isophotes. The
center is 3
off the brightest pixel associated to
a small bar-like central structure of size
followed by a thin, star-forming, blue spiral arm feature
towards north-east.
The final profile shows a downbending break at 35
corresponding to the inner lopsided disk thus classified as a
Type II-AB break, although this is just at the radius of an outer
ring (best visible in the colour image).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f168.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f169.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg334.gif) |
NGC 7437: Type II-CT
J225810.0+141832 .SXT7. 7.1 -18.88 1.8 2190
Small galaxy close to the edge of the SDSS field but almost
complete.
Similar to NGC 5300 the final profile shows the prototypical
Type II.o-CT behaviour. A sharp break at 40
,
corresponding roughly
to the end of the apparent flocculent spiral arm structure, followed by
a downbending profile. Although classified as SAB there is no obvious
structure visible which could be identified with a bar. Using the
beginning spiral arms as an upper limit (
)
the break
is still too far out for a normal Type II.o-OLR break.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f170.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f171.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg335.gif) |
NGC 7606: Type II-CT
J231904.8-082906 .SAS3. 3.2 -21.38 4.3 2187
Galaxy with multiple thin spiral arms.
The final profile exhibits clearly a break at 110
corresponding roughly to the end of the visible spiral arm
structure, following part of the ring enclosing an apparent
hole (enhanced dust extinction?) in the disk towards the north-west.
Since the galaxy is classified as SA and no bar structure visible
the break is a Type II-CT.
The apparent upbending of the profile beyond 190
is not related to a sky error but due to a changing ellipticity in
the very outer disk (maybe due to a warp?).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f172.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f173.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg336.gif) |
PGC 006667 UGCA 021: Type II-AB
J014910.2-100345 .SBS7. 7.1 -18.77 2.9 1887
A large scale gradient (from top to bottom) in the background of
the
band image is removed with linear fit.
Galaxy in NGC 701 group (see above).
Final profile shows a bump at 20
due to the spiral
arms starting from the bar-like center. The clear downbending break
at 75
corresponds to a transition from the inner more
symmetric to an asymmetric, extended outer disk region and is
therefore classified as Type II-AB.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f174.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f175.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg337.gif) |
UGC 02081: Type II-CT
J023600.9+002512 .SXS6. 5.8 -18.56 1.8 2549
Galaxy close to the edge of the SDSS field but almost complete.
The final profile shows a downbending break starting around
55
(clearly at 70
)
with a very faint,
but symmetric light distribution beyond. Although classified as SAB
the bar is not obvious from the image but the spiral arms allow to
estimate an upper limit of
.
Therefore the break
(which is not produced by a sky error) is classified Type II-CT.
The profile published in de Jong & van der Kruit (1994) is not deep enough to
confirm the downbending.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f176.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f177.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg338.gif) |
UGC 04393: Type I
J082604.3+455803 .SB?.. 5.5 -19.49 2.2 2290
Galaxy is classified as SB and the inner region is dominated by an
elongated bar-like structure of size
.
Therefore
this region is excluded from the fit.
The extended bar, having a kind of double nucleus, is slightly
offcenter (central dip in profile) compared to the center obtained
from the outer isophotes and is followed by a single, narrow
spiral arm like structure extending south-west.
In the outer disk there is an additional, faint spiral arm visible
towards the south-east.
There is also a very faint shell or stream-like structure detected,
detached from the galaxy about
away to the north-west.
The inclination (ellipticity) and PA are rather uncertain since
they are continuously changing towards the outer disk.
The final profile, beyond the inner bar region, is classified as Type I,
due to the uncertain ellipticity and the asymmetric outer disk with the
spiral arm, although there are two possible breaks visible at
60
and 80
,
of which the first could
correspond to a Type II.o-OLR break and the latter to a Type III.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f178.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f179.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg340.gif) |
UGC 06309: Type II.i
J111746.4+512836 .SB?.. 5.0 -19.63 1.3 3097
There is a small BCG (MRK 1445) about
away
at roughly the same distance (v=2863 km s-1 ).
Galaxy exhibits very unusual, disturbed shape. The inner disk is
dominated by a narrow bar of size
followed
by two asymmetric spiral arms (one highly wrapped, forming an inner
ring, the other almost extending straight). The disk beyond the
spiral arms is also highly asymmetric and more egg-shaped with a
region of low emission (high extinction?) towards the south-east,
which makes the bar appear to be offcentered. However, the center
from the very outer isophotes coincides again with the nucleus
inside the bar.
The extended dip and peak structure around
in the
final profile corresponds to the inter-arm region, respectively
the pseudoring build by the arms, so the break around this radius
is classified as Type II.i.
This should be used with caution, since alternatively one can argue
for a break at 35
,
at about twice the bar radius thus
a Type II.o-OLR break, while excluding the region between 15-30
.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f180.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f181.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg341.gif) |
UGC 06518: Type II.i
J113220.4+535417 ...... 4.3 -18.94 1.0 3044
Small galaxy where, although not classified as barred in NED or LEDA,
there is clearly a bar of size
visible, with indication
for a ring-like structure around, already reported by Takase & Miyauchi-Isobe (1984).
Despite the possibility to argue for a break at 15
in
the final profile we classify the galaxy as Type II.i excluding the
region inside
from the fit.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f182.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f183.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg344.gif) |
UGC 06903: Type II.o-CT
J115536.9+011415 .SBS6. 5.8 -18.80 2.5 1916
Very bright star in FOV but galaxy not influenced.
Final profile shows clearly a downbending break around
65
corresponding roughly to the end of the visible
spiral arm structure and classified Type II.o-CT, since the size of the
bar with
is too small.
The extended bump between
is related to the
inner two, highly wrapped (pseudoring?) spiral arms.
The downbending shape is consistent with the profile shown in
Jansen et al. (2000) (cf. ID 99).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f184.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f185.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg346.gif) |
UGC 07700: Type II.o-CT
J123232.8+635238 .SBS8. 7.8 -18.50 1.8 3239
There is a very bright star in the FOV but the galaxy is not influenced.
On same image there is an edge-on companion (S0/a galaxy NGC 4512) at
similar distance (v=2536 km s-1 ) visible.
Ellipticity obtained from the very outer isophotes and not
by the usual
criterion.
The final profile shows clearly a downbending behaviour outside
the bar region. The bar is about
in size and
slightly offcentered (by 5
)
compared to the center
obtained from the outer, symmetric isophotes. This causes the
dip at the center.
The extended break region is not exponential but shows a
curvature, but still one could define two break radii at
40
and 50
.
The region in between
corresponds to a single spiral arm extending towards the
north-east.
Although the first one would roughly classify as a Type II.o-OLR break
we used a single break slightly further out and classified the
galaxy as Type II.o-CT.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f186.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f187.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg349.gif) |
UGC 08041: Type II.o-CT
J125512.7+000700 .SBS7. 6.8 -18.62 3.2 1376
Galaxy close to our high axis ratio limit and not influenced by
the very bright star in FOV.
The inner disk with a bright nucleus in the bar and weak spiral arm
structure extends to about 100
,
followed by a rather
asymmetric, lopsided outer disk extending to the south-west.
Centering on the outer isophotes (
)
would be
off by more than 10
.
The final profile shows a downbending break at 75
roughly corresponding to the end of the spiral structure.
Since the bar is only of size
the break,
at significantly more than twice the bar radius, is classified as
Type II.o-CT.
The fixed ellipse leaves the inner symmetric disk at about
100
into the asymmetric outer part causing
the apparent upbending in the profile, which probably increases
the fitted outer scalelength.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f188.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f189.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg352.gif) |
UGC 08084: Type II.o-OLR
J125822.4+024733 .SBS8. 8.1 -18.61 1.3 2824
Small galaxy dominated by an inner offcentered, asymmetric bar of
size
,
which appears to be z-shaped together with
the two spiral arms. The center is obtained from outer isophotes
(
)
and is about 12
away from the
brightest pixel in bar, which is responsible for the flat inner profile.
The final profile shows clearly a downbending break at 40
corresponding to the spiral arms forming a kind of pseudoring in the
outer parts. Since the break is at about twice the bar size the galaxy
is classified as Type II.o-OLR.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f190.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f191.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg354.gif) |
UGC 08237: Type II.o-OLR
J130854.5+621823 PSB.3* 3.2 -19.61 0.9 3120
Galaxy is isolated according to Prada et al. (2003). The similar sized
companion, only
away, is a confirmed background galaxy
(UGC 08234, v=8100 km s-1 ).
Background needs extended mask due to straylight from a very bright
star off the field.
UGC 08237 is a small galaxy dominated by a bright, thick bar of
size
(producing the shoulder in the final profile)
followed by two nearly symmetric, wrapped spiral arms forming a pseudoring
peaking at 20
.
Similar to NGC 5701 (an early-type SB0/a galaxy from Erwin et al. (2006))
one could define a break at 25
just outside of the pseudoring
forming the region
which is no longer well fitted by an
exponential profile. Erwin et al. (2006) call these systems "extreme'' OLR
breaks, so we also classify the galaxy as Type II.o-OLR and apply a crude
fit to obtain an inner scalelength.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f192.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f193.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg356.gif) |
UGC 08658 Holmberg V: Type II-CT
J134039.9+541959 .SXT5. 5.1 -19.91 2.6 2285
Galaxy close to the border of the SDSS field but almost complete. Although
classified as SAB, the bar size is not obvious from the image, but could be
restricted by the spiral arms to be maximal
.
The shoulder in the final profile at 20
is due to the inner
spiral arms being aligned with the ellipse.
There is a weak break at 65
visible which roughly
coincides with the end of the inner spiral arm structure, although
there are maybe two faint extensions into the outer disk.
Since being at significantly more than two bar radii we classify
the break as Type II-CT.
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f194.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f195.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg359.gif) |
UGC 09741 NGC 5875A: Type III
J150833.5+521746 .S?... 6.0 -18.54 0.9 2735
The patch of faint light on the image towards the north-west
is caused by straylight from a very bright star off field, but
the galaxy is not affected.
Very small galaxy dominated by a long, narrow bar of size
,
enclosed by a ring like structure building the
inner
disk.
The photometric inclination (ellipticity) and PA is obtained from
the outer disk at 45
and not from the
ellipse.
Although it is possible to fit the profile beyond 17
with a single exponential the offset inside would be too large to
be assigned solely to a bulge component of a typical Sc galaxy. In
addition, an extended bulge component is also not visible on the
image inside the narrow bar.
Thus we argue for a break, classified as Type III, at 25
followed by an upbending profile into the symmetric featureless
outer disk.
The shape of the profile is consistent with the one shown by
Jansen et al. (2000) (cf. ID 166).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f196.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f197.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg362.gif) |
UGC 09837: Type II-CT
J152351.7+580311 .SXS5. 5.1 -19.45 1.8 2938
Although classified as SAB, the bar size is not obvious from the
image, but could be restricted to be maximal
by the two symmetric spiral arms starting beyond the bulge/bar
region out to
.
Further out, there is more asymmetric spiral arm structure visible,
with one arm almost forming a ring-like section, which makes the
photometric inclination (ellipticity) and PA determination
impossible at the
ellipse.
Since the ring like section extends to the end of our free ellipse
fit, we set the ellipticity to 0.05 (round).
In the final profile there is a break visible at 50
just beyond the bump produced by the ring-like spiral arm.
Since this break is at significantly more than two times the upper
limit for the bar radius we classify the break as Type II-CT.
The deep surface photometry from Pohlen et al. (2002) is consistent
with the results here (cf. Fig. 3) aside from this bump
produced by the outer spiral arm, which seems to be suppressed in
their averaged profile.
The downbending shape with a break at 50
is
consistent with the profile shown by van der Kruit (1987).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f198.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f199.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg363.gif) |
UGC 10721: Type III
J170825.6+253103 .S..6? 5.8 -19.68 1.2 3118
Small galaxy close to our high axis ratio limit so the dust
may get important. Galaxy shows an inner apparently inclined
disk with a nucleus and some thin spiral arms sitting in an almost
round outer isophote most probably related to a vertical structure
(halo or thick disk). Thus the photometric inclination (ellipticity)
and PA are highly uncertain since continously changing with radius.
The shoulder at 12
in the final profile corresponds
to an aligned spiral arm.
There is a clear break visible at 40
followed by an
upbending profile which is classified as Type III, associated to the
transition between inner and outer disk (vertical structure?), so
to be taken with some caution. The sharp transition in the profile
argues against a thick disk.
The upbending behaviour is confirmed by the profile from
Courteau (1996).
|
![\begin{figure}\includegraphics[width=5.7cm,angle=270]{4883f200.ps}\par\hspace*{-0.5cm}\includegraphics[width=6.1cm,angle=270]{4883f201.ps}
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg364.gif) |
UGC 12709: Type II-CT
J233724.0+002327 .SXS9. 8.3 -19.05 3.0 2672
This is a faint, low surface brightness galaxy without a well
defined center, so the centering (obtained from the 80
ellipse) and the photometric inclination (ellipticity) and PA
(obtained at 70
)
are uncertain.
The offcentered outer disk is reflected by the central dip in the
final profile, which shows a clear downbending break at
70
corresponding roughly to the end of the
flocculent starforming patches.
Although classified as SAB the central region ( 10
)
is
too fuzzy to argue for or against a bar, but in both cases it is to small
to be responsible for the break, which is therefore classified as Type II-CT.
|
Appendix B: Rejected galaxies
![\begin{figure}\par\includegraphics[width=5.7cm,angle=270]{4883f202.ps}\includegr...
...883f206.ps}\includegraphics[width=5.7cm,angle=270]{4883f207.ps}\par
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg365.gif) |
Figure B.1:
Galaxies rejected from the original LEDA-SDSS(DR2) sample:
SDSS colour plates of NGC 0428,
NGC 0988,
NGC 2712,
NGC 3023,
NGC 4116, and
NGC 4496A
(from left to right and top to bottom). |
![\begin{figure}\par\includegraphics[width=5.7cm,angle=270]{4883f208.ps}\includegr...
...ludegraphics[width=5.7cm,angle=270]{4883f214.ps}\hspace*{4cm}}
\par
\end{figure}](/articles/aa/full/2006/30/aa4883-06/Timg366.gif) |
Figure B.1:
continued. Galaxies rejected from the original LEDA-SDSS(DR2) sample
SDSS colour plates of NGC 4900,
NGC 5218,
NGC 5364,
PGC 032356,
UGC 04684,
UGC 06162, and
UGC 09215
(from left to right and top to bottom). |
Copyright ESO 2006