A&A 379, 54-71 (2001)
DOI: 10.1051/0004-6361:20011275
H. M. Hernández-Toledo1 - I. Puerari2
1 - Instituto de Astronomía - UNAM - Apartado Postal 70-264,
04510 México DF, México
2 - Instituto Nacional de Astrofísica, Optica y Electrónica,
Calle Luis Enrique Erro 1, 72840 Tonantzintla, Puebla, México
Received 28 February 2001 / Accepted 21 August 2001
Abstract
We present multicolour broad band (BVRI) photometry
for a sample of 33 spiral-spiral (S+S) binary galaxies drawn
from the Karachentsev Catalogue of Isolated Pairs of Galaxies
(KPG). The data is part of a joint observational programme
devoted to systematic photometric study of one of the most
complete and homogeneous pair samples available in the
literature. We present azimuthally averaged colour and surface
brightness profiles, colour index (B-I) maps, B band and
sharp/filtered B band images as well as integrated
magnitudes, magnitudes at different circular apertures
and integrated colours for each pair. Internal and external
data comparisons show consistency within the estimated
errors. Two thirds of the sample have total aperture
parameters homogeneously derived for the first time. After
reevaluating morphology for all the pairs, we find a change
in Hubble type for 24 galaxies compared to the original
POSS classifications. More than half of our pairs show
morphological concordance which could explain, in part,
the strong correlation in the (B-V) colour indices
(Holmberg Effect) between pair components. We find
a tendency for barred galaxies to show grand design
morphologies and flat colour profiles. The measurements
will be used in a series of forthcoming papers where we try
to identify and isolate the main structural and photometric
properties of disk galaxies at different stages of interaction.
Key words: galaxies: spiral - galaxies: structure - galaxies: photometry - galaxies: interactions - galaxies: fundamental parameters - galaxies: kinematics and dynamics
Two-dimensional broad-band photometry has been systematically applied to the study of binary galaxy structure and dynamics, only in the past two decades. The mid to late 70's saw an astronomical debate that led to the recognition that gravitational interaction is an important factor in galactic evolution affecting directly properties such as size, morphological type, luminosity, star formation rate, and mass distribution (Sulentic 1976; Larson & Tinsley 1978; Stocke 1978). According to current popular models of galaxy formation, galaxies are assembled through a hierarchical process of mass aggregation, dominated either by mergers (Kauffmann et al. 1993; Baugh et al. 1996) or by gas accretion (Avila-Reese et al. 1998; Avila-Reese & Firmani 2000). In the light of these models, the influence of environment factors and interaction phenomena in the shaping and star formation of the disks is natural, at least for a fraction of the present-day galaxy population. Examples are galaxy harassment in clusters (Moore et al. 1996), tidal stirring of dwarf irregulars near giant galaxies (Mayer et al. 2001), tidally induced star formation (Lacey & Silk 1991; Kauffmann et al. 2001). See also Dultzin-Hacyan (1997) for a non-biased review.
For binary galaxies, current ideas suggest that most physical pairs are morphologically concordant, that is, with components showing similar initial star formation and angular momentum properties. Evidence in favour of these ideas come from the colour correlations (Holmberg effect) observed for components of pairs, although very few photometric data supporting this correlation exists at present. The large number of (S+S) pairs in The Catalogue of Isolated Pairs of Galaxies in the Northern Hemisphere (KPG, Karachentsev 1972) means that for a flux-limited sample ( mzw = 15.7), almost six out of every ten pairs are of the (S+S) type, suggesting that a considerable number of them must be physical binaries.
Redshift information, available for the whole (S+S)
sample, suggests that most are likely to be physically
proximate. Digital Sky Survey images show that most
have visible signs of disturbance; bridges, tails, common
envelopes and distortions that are regarded as evidence
for gravitational interaction. In addition, statistical
studies indicate that a high fraction (%)
show an enhancement in the optical and FIR emission
(Xu & Sulentic 1991; Hernández-Toledo et
al. 1999). This enhancement is interpreted as
a by-product of interaction-induced star formation activity
in physical binaries.
One of the most important lessons that emerges from statistical studies of interacting galaxies is that if we want to have a better understanding of the connection between interactions, photometric structural parameters and optical morphology, it is necessary to obtain accurate photometry for complete and homogeneous interacting galaxy samples. The results can then be interpreted by applying similar methods to well-matched comparison samples (isolated, presumably undisturbed galaxies). Some efforts in this direction are Bergvall & Johansson (1995), Reduzzi & Rampazzo (1996), Márquez & Moles (1996), Laurikainen et al. (1998), Jansen et al. (2000), Márquez & Moles (1999), and de Jong & van der Kruit (1994).
Our main goal is to obtain an homogeneous set of broad-band observations for most (if not all) of the (S+S) pairs in the Karachentsev Catalogue. The relative simplicity, compared to groups and clusters along with the size, brightness limit and morphological diversity, offer us a unique opportunity to realize accurate photometric observations for a statistically significant number of pairs where a less confused interpretation of the photometric properties of disk galaxies at different stages of interactions (and its relationship to optical morphology) is possible.
We present in this first paper of a series, our photometric data with emphasis on the morphological properties in a subset of 33 (S+S) pairs. The structure of the paper is as follows. Section 2 summarizes some limitations and biases in the (S+S) sample which are relevant to our photometric study. Section 3 presents the observations, reduction techniques and a comparison of our estimated total magnitudes against those in the literature. A discussion on the related errors is also included. Section 4 shows a discussion based on the estimated colour indices, observed optical morphologies and (colour and surface brightness) profiles for each component galaxy. The systematics of morphological distortions induced by the interactions are commented in the light of current models. Section 5 is a summary of the conclusions achieved. Finally, an Appendix is devoted to the presentation of magnitudes at three different concentric circular apertures.
Through the main optical observatories in México (Observatorio
Astronómico Nacional at San Pedro Mártir in Baja California
and Observatorio Astrofísico Guillermo Haro in Cananea)
we have started a joint observational programme devoted
to obtain uniform photometric data for one of the most complete
and homogeneous pair samples currently available. The sample of
disk-disk (S+S) pairs amounts to more than 300 pairs from
a total of 602 pairs in the KPG catalogue. The observations
were begun since January 1999. The CCD BVRI images reported
here (in the Cousins system) were obtained with a LFOSC
detector attached to the 2.1 m telescope, at Observatorio
Guillermo Haro, Cananea, Sonora, México, covering an area
of about
,
with a scale of
1
/pixel.
Since our goal is to observe all or most of the KPG (S+S) sample, we have applied no special strategy in selecting the current subset of 33 (S+S) pairs. Available observing time and weather conditions were the main factors limiting the number of observed pairs. This will be the observational strategy for the next reports up to the point where most of the (S+S) sample is observed. The selection criteria and statistical properties for the (S+S) sample that are most relevant to the present and further photometric analysis are stated here.
A journal of the first set of the photometric observations is
given in Table 1. Column (1) gives the original
catalogued number, Cols. (2)-(9) give the number of frames per
filter, the integration time (in seconds) and seeing conditions
(in arcsec).
Galaxy pair | B | <B>FWHM | V | <V>FWHM | R | <R>FWHM | I | <I>FWHM |
KPG64 |
![]() |
2.4 |
![]() |
2.3 |
![]() |
2.6 |
![]() |
3.1 |
KPG68 |
![]() |
2.3 |
![]() |
2.5 |
![]() |
2.3 |
![]() |
2.8 |
KPG75 |
![]() |
2.1 |
![]() |
2.2 |
![]() |
2.1 |
![]() |
2.7 |
KPG88 |
![]() |
2.4 |
![]() |
2.5 |
![]() |
2.6 |
![]() |
3.3 |
KPG98 |
![]() |
2.6 |
![]() |
2.5 |
![]() |
3.1 |
![]() |
3.1 |
KPG102 |
![]() |
2.1 |
![]() |
2.4 |
![]() |
2.4 |
![]() |
2.6 |
KPG103 |
![]() |
2.7 |
![]() |
2.5 |
![]() |
2.5 |
![]() |
2.8 |
KPG108 |
![]() |
2.5 |
![]() |
2.5 |
![]() |
2.2 |
![]() |
2.4 |
KPG112 |
![]() |
2.5 |
![]() |
2.3 |
![]() |
2.2 |
![]() |
2.8 |
KPG125 |
![]() |
2.6 |
![]() |
2.9 |
![]() |
3.2 |
![]() |
3.6 |
KPG136 |
![]() |
2.7 |
![]() |
2.5 |
![]() |
2.3 |
![]() |
2.9 |
KPG141 |
![]() |
2.4 |
![]() |
2.3 |
![]() |
2.2 |
![]() |
2.5 |
KPG150 |
![]() |
2.7 |
![]() |
2.4 |
![]() |
2.4 |
![]() |
2.7 |
KPG151 |
![]() |
2.4 |
![]() |
2.6 |
![]() |
2.2 |
![]() |
3.3 |
KPG156 |
![]() |
2.6 |
![]() |
2.6 |
![]() |
2.9 |
![]() |
3.6 |
KPG159 |
![]() |
3.6 |
![]() |
3.4 |
![]() |
3.2 |
![]() |
3.5 |
KPG160 |
![]() |
2.5 |
![]() |
2.1 |
![]() |
2.3 |
![]() |
2.8 |
KPG168 |
![]() |
3.1 |
![]() |
2.9 |
![]() |
2.9 |
![]() |
3.5 |
KPG195 |
![]() |
3.0 |
![]() |
3.2 |
![]() |
2.6 |
![]() |
2.5 |
KPG211 |
![]() |
2.7 |
![]() |
2.5 |
![]() |
3.0 |
![]() |
3.7 |
KPG216 |
![]() |
2.9 |
![]() |
2.7 |
![]() |
2.3 |
![]() |
2.4 |
KPG249 |
![]() |
3.0 |
![]() |
3.3 |
![]() |
3.5 |
![]() |
3.4 |
KPG295 |
![]() |
3.0 |
![]() |
3.2 |
![]() |
3.1 |
![]() |
2.9 |
KPG302 |
![]() |
2.3 |
![]() |
2.3 |
![]() |
2.2 |
![]() |
2.7 |
KPG313 |
![]() |
3.3 |
![]() |
3.2 |
![]() |
3.1 |
![]() |
2.6 |
KPG332 |
![]() |
2.9 |
![]() |
2.9 |
![]() |
2.5 |
![]() |
2.6 |
KPG347 |
![]() |
2.8 |
![]() |
3.0 |
![]() |
2.5 |
![]() |
2.6 |
KPG389 |
![]() |
3.5 |
![]() |
3.6 |
![]() |
3.2 |
![]() |
2.6 |
KPG396 |
![]() |
2.4 |
![]() |
2.7 |
![]() |
2.5 |
![]() |
2.7 |
KPG404 |
![]() |
2.7 |
![]() |
2.9 |
![]() |
3.1 |
![]() |
2.4 |
KPG426 |
![]() |
2.9 |
![]() |
3.1 |
![]() |
3.2 |
![]() |
3.0 |
KPG440 |
![]() |
2.4 |
![]() |
3.0 |
![]() |
2.8 |
![]() |
2.6 |
KPG455 |
![]() |
2.3 |
![]() |
2.5 |
![]() |
2.6 |
![]() |
3.1 |
Table 2 reports some relevant information
for the observed pairs coming from the literature. Column (1) is the KPG catalogued number, Col. (2) reports other
identifications, Col. (3) the apparent B magnitude from
the Nasa Extragalactic Database (NED), Col. (4) the linear
separation (in kpc), Col. (5) the radial velocity in
km s-1 from NED, and finally, Col. (6) gives the major
axis diameter (at
)
for each component galaxy
(in kpc).
KPG Number | Identif. | B mag | x12 (kpc) |
![]() |
A25 (kpc) |
KPG64A | UGC 01810 | 13.42(p) | 39.5 | 7563 | 55.8 |
KPG64B | UGC 01813 | 15.08(p) | 7335 | 27.4 | |
KPG68A | NGC 0935 | 13.63(p) | 17.4 | 4142 | 29.3 |
KPG68B | IC 1801 | 14.56(p) | 4023 | 19.3 | |
KPG75A | UGC 02222 | 14.56(p) | 21.5 | 4913 | 32.0 |
KPG75B | UGC 02225 | 15.21(p) | 4965 | 18.6 | |
KPG88A | UGC 02627 | 14.89(a) | 32.7 | 4224 | 30.8 |
KPG88B | UGC 02629 | 15.28(p) | 4128 | 15.1 | |
KPG98A | UGC 02954 | 15.23(p) | 41.2 | 5306 | 17.4 |
KPG98B | MRK 1081 | 15.15(p) | 5345 | 16.0 | |
KPG102A | CGCG 393-070 | 15.50(p) | 34.4 | 10778 | 21.0 |
KPG102B | UGC 03136 | 15.00(p) | 10674 | 34.8 | |
KPG103A | CGCG 420-003 | 15.70(p) | 55.2 | 8313 | 20.3 |
KPG103B | UGC 03179 | 14.46(p) | 8337 | 28.4 | |
KPG108A | UGC 03405 | 15.32(p) | 33.9 | 3738 | 20.1 |
KPG108B | UGC 03410 | 14.99(p) | 3921 | 29.8 | |
KPG112A | UGC 03445 | 14.25(p) | 9.7 | 3119 | 21.3 |
KPG112B | UGC 03446 | 13.86(p) | 3116 | 21.2 | |
KPG125A | NGC 2341 | 13.84(a) | 50.9 | 5227 | 24.9 |
KPG125B | NGC 2342 | 13.10(a) | 5276 | 29.1 | |
KPG136A | CGCG 086-028 | 14.80(p) | 37.8 | 9907 | 31.1 |
KPG136B | CGCG 086-029 | 15.00(p) | 9813 | 32.1 | |
KPG141A | UGC 04005 | 14.60(p) | 89.8 | 5044 | 31.8 |
KPG141B | CGCG 030-014 | 14.80(p) | 4896 | 14.4 | |
KPG150A | NGC 2486 | 14.16(a) | 99.3 | 4649 | 29.5 |
KPG150B | NGC 2487 | 13.23(a) | 4841 | 45.6 | |
KPG151A | UGC 04133 | 16.00(p) | 32.5 | 9130 | 50.5 |
KPG151B | UGC 04134 | 15.37(p) | 8968 | 32.6 | |
KPG156A | NGC 2535 | 13.31(a) | 27.7 | 4097 | 30.9 |
KPG156B | NGC 2536 | 14.70(a) | 4142 | 17.0 | |
KPG159A | CGCG 088-052 | 15.60(p) | 26.0 | 5232 | 9.9 |
KPG159B | UGC 04286 | 14.32(p) | 5143 | 19.9 | |
KPG160A | NGC 2544 | 13.80(a) | 17.4 | 2828 | 16.0 |
KPG160B | CGCG 331-037 | 15.50(p) | 3589 | 11.0 | |
KPG168A | NGC 2648 | 12.74(p) | 17.6 | 2060 | 23.1 |
KPG168B | CGCG 060-036 | 15.40(p) | 2115 | 9.2 | |
KPG195A | NGC 2798 | 13.04(a) | 11.5 | 1726 | 16.3 |
KPG195B | NGC 2799 | 14.32(p) | 1865 | 11.3 | |
KPG211A | NGC 2959 | 13.65(p) | 26.8 | 4429 | 29.3 |
KPG211B | NGC 2961 | 15.52(p) | 4501 | 12.2 | |
KPG216A | NGC 3018 | 14.13(p) | 17.8 | 1863 | 6.45 |
KPG216B | NGC 3023 | 13.50(p) | 1879 | 14.7 | |
KPG249A | NGC 3395 | 12.40(a) | 8.8 | 1625 | 10.5 |
KPG249B | NGC 3396 | 12.63(p) | 1625 | 12.3 | |
KPG295A | NGC 3786 | *13.24(p) | 14.9 | 2678 | 19.2 |
KPG295B | NGC 3788 | 13.46(p) | 2699 | 13.9 | |
KPG302A | NGC 3893 | 11.16(s) | 13.9 | 977 | 17.1 |
KPG302B | NGC 3896 | 13.89(p) | 980 | 5.9 | |
KPG313A | IC 0749 | 12.92(s) | 10.9 | 784 | 7.5 |
KPG313B | IC 0750 | 12.94(s) | 701 | 9.1 | |
KPG332A | NGC 4298 | 12.04(s) | 9.5 | 1135 | 10.3 |
KPG332B | NGC 4302 | 12.50(s) | 1149 | 13.0 | |
KPG347A | NGC 4567 | 12.06(s) | 10.8 | 2274 | 20.2 |
KPG347B | NGC 4568 | 11.68(s) | 2255 | 29.3 | |
KPG389A | NGC 5257 | *13.50(p) | 36.6 | 6798 | 39.0 |
KPG389B | NGC 5258 | *13.49(p) | 6757 | 37.8 | |
KPG396A | UGC 08713 | 15.25(p) | 28.6 | 4956 | 24.3 |
KPG396B | UGC 08715 | 14.50(p) | 4517 | 22.7 |
KPG Number | Identif. | B mag | x12 (kpc) |
![]() |
A25 (kpc) |
KPG404A | NGC 5394 | 13.70(a) | 26.2 | 3472 | 22.8 |
KPG404B | NGC 5395 | 12.10(a) | 3491 | 34.1 | |
KPG426A | UGC 09376 | 14.70(p) | 26.8 | 7676 | 40.6 |
KPG426B | CGCG 220-030 | 14.89(p) | 7764 | 46.8 | |
KPG440A | NGC 5774 | 12.74(s) | 27.2 | 1567 | 20.9 |
KPG440B | NGC 5775 | 12.24(s) | 1681 | 21.2 | |
KPG455A | NGC 5857 | 13.86(a) | 38.4 | 4682 | 21.6 |
KPG455B | NGC 5859 | 13.27(a) | 4764 | 41.7 |
(a) Total (asymptotic) magnitude in the B system, derived
by extrapolation from
photoelectric aperture-magnitude data.
(s) Total asymptotic magnitude in the B system, derived
by extrapolation from
(surface) photometry with photoelectric zero point.
(p) Photographic magnitude reduced to the
system.
Images were debiased, trimmed, and flat-fielded using
standard IRAF procedures. First, the bias level of the CCD was subtracted
from all exposures. A run of 5-10 bias images was obtained per
night, and these were combined into a single bias frame which was
then applied to the object frames. The images were flat-fielded
using sky flats taken in each filter at the beginning and/or at
the end of each night.
Photometric calibration was achieved by nightly
observations of standard stars of known magnitudes
from the "Dipper Asterism'' M 67 star cluster
(Chevalier & Ilovaisky 1991).
A total of 29 standard stars with a colour range
and a similar range in (V-I) were
observed. The principal extinction coefficients in B, V,
R and I as well as the colour terms were calculated
according to the following equations:
In a first iteration, a constant value associated with the
sky background was subtracted using an interactive procedure
that allows the user to select regions on the frame free
of galaxies and bright stars. However, occasionally, at the
end of the reduction procedure, we still had images with a
noticeable gradient in the sky background. For these images,
a fifth-order polynomial was fitted and subtracted from the
entire frame. After this processing, the sky background is
usually flat to a level
%. Errors in determining
the sky background, are, in fact, probably the dominant
source of error in the estimation of the colour and surface
brightness profiles. For this reason, we decided to apply
this polynomial correction to all the images in this work.
The most energetic cosmic-ray events were automatically
masked using the COSMICRAYS task and field stars were
removed using the IMEDIT task when necessary. Within the
galaxy itself, care was taken to identify superimposed stars.
A final step in the basic reduction involved registration of
all available frames for each galaxy and in each filter to
within
pixel. This step was performed by measuring
centroids for foreground stars on the images and then performing
geometric transformations using GEOMAP and GEOTRAN tasks in
IRAF.
Elliptical surface brightness contours were fitted using the STSDAS package ISOPHOTE. An initial starting guess for the ellipse-fitting routine was provided interactively by estimating points that represent the ends of the major and minor axis at an isophotal level of relatively high signal-to-noise ratio. Since we are interested on the mean global properties of these profiles and not in their detailed structure, we report azimuthally averaged profiles for spirals by fitting ellipses with a fixed position angle and ellipticity previously determined on the external isophotes of each galaxy. A more detailed analysis and interpretation will be presented in a forthcoming paper (Hernández-Toledo & Puerari, in preparation).
Total magnitudes can be calculated by analytically extrapolating a fitting of a disk beyond the outermost isophote to infinity. However, disk fitting is notoriously fraught with uncertainty (cf. Knapen & van der Kruit 1991). Alternatively, we estimate in this work a total magnitude computed from polygonal apertures chosen interactively to assure that they are large enough to contain the whole galaxy and still small enough to limit the errors due to the sky error and light contamination from a neighbor galaxy. This is achieved in each band by using polygonal apertures with and without the the sky background removed within POLYPHOT routines in IRAF. In an Appendix, we are also reporting total magnitudes at three different circular apertures by using the PHOT routines in IRAF. Foreground stars within the aperture were removed interactively. In some cases, the separation of the galaxies allowed us to model the light distribution in each galaxy and then to try an iterative subtraction as reported in Junqueira et al. (1998). In cases where this procedure was not possible, our estimations must be taken with care. See Table 3 and comments on individual objects.
An estimation of the errors in our photometry involves
two parts: 1) the procedures to obtain instrumental
magnitudes and 2) the uncertainty when such instrumental
magnitudes are transformed to the standard system. For 1),
notice that the magnitudes produced at the output of the IRAf
routines (QPHOT, PHOT and POLYPHOT) have a small error
that is internal for those procedures. Since we also have
applied extinction corrections to the instrumental magnitudes
in this step, our estimation of the errors are mainly
concerned with these corrections and the estimation of the
airmass. After a least square fitting, the associated errors
to the slope for each principal extinction coefficient
are;
,
,
and
.
An additional error
from the
airmass routines in IRAF was also considered.
For 2), the zero point and first order colour
terms are the most important to consider. After
transforming to the standard system, by adopting our
best-fit coefficients, the formal errors from the assumed
relations for
were 0.05, 0.04, 0.04 and 0.04 in
B, V, R and I and 0.04, 0.03, 0.03 and 0.04 for
.
To estimate the total error in each band, it is
necessary to use the transformation equations and then
propagate the errors. Total typical uncertainties are
0.15, 0.14, 0.15 and 0.14 in B, V, R and I bands,
respectively.
The estimated total magnitudes in this work were compared against other external estimations reported in the literature. This has been done for: 1) the standard stars and 2) those paired galaxies in common with other works.
For the standard stars, a comparison of our CCD magnitudes
against those reported in Chevalier & Ilovaisky
(1991) for 29 stars in common, are
shown in Fig. 1.
![]() |
Figure 1: Comparison between our estimated magnitudes and those from Chevalier & Ilovaisky (1991) for 29 standard stars in common. |
Open with DEXTER |
Figure 1 shows no significant deviations
between our CCD magnitudes and the standard star magnitudes.
According to these results, a
,
or a
similar value, could be expected as the typical error for our
magnitude estimations in paired galaxies. This is in agreement
with our error estimations.
We begin with a comparison in Fig. 2
of our total magnitudes in B and V bands
and those reported in the RC3 Catalogue (de Vaucouleurs
et al. 1991).
![]() |
Figure 2: Comparison between our total B and V magnitudes and total magnitudes from RC3 Catalogue. |
Open with DEXTER |
We find that, except for three galaxies (KPG347B,
KPG404B and KPG440A) the agreement with our measures is
reasonably good. Rms values from our comparisons
are 0.17 and 0.13 mag in B and V bands respectively.
However, as noted in Table 3
KPG347 and KPG404 involve two overlapping pairs (CP)
where our iterative magnitude estimation procedure could
produce some error. In addition, the associated errors in
B and V magnitudes reported in RC3 are 0.1 mag
for KPG347B and KPG440A and 0.2 mag for KPG404B.
KPG | B | V | R | I | B-V | B-I |
![]() |
![]() |
Notes |
KPG64A | 13.70 | 12.92 | 12.37 | 11.70 | 0.78 | 2.00 | 13.32 | 0.66 | |
KPG64B | 15.17 | 14.21 | 13.66 | 12.98 | 0.96 | 2.18 | 14.44 | 0.75 | |
KPG68A | 13.56 | 12.82 | 12.19 | 11.51 | 0.73 | 2.05 | 13.02 | 0.58 | CP |
KPG68B | 14.73 | 13.98 | 13.31 | 12.65 | 0.75 | 2.08 | 14.07 | 0.58 | CP |
KPG75A | 14.62 | 13.68 | 13.19 | 12.18 | 0.95 | 2.44 | 14.07 | 0.80 | |
KPG75B | 15.36 | 14.49 | 13.99 | 12.97 | 0.87 | 2.39 | 14.50 | 0.65 | |
KPG88A | 15.06 | 13.69 | 12.90 | 12.17 | 1.37 | 2.89 | 14.13 | 1.15 | |
KPG88B | 16.12 | 14.85 | 14.11 | 13.44 | 1.27 | 2.68 | 15.21 | 1.05 | |
KPG98A | 15.62 | 15.34 | 14.08 | 13.28 | 0.28 | 2.34 | 14.76 | 0.10 | |
KPG98B | 15.51 | 14.22 | 13.03 | 12.07 | 1.29 | 3.44 | 14.89 | 1.12 | |
KPG102A | 15.68 | 15.18 | 14.84 | 13.87 | 0.51 | 1.81 | 14.98 | 0.29 | |
KPG102B | 15.06 | 14.57 | 14.22 | 13.42 | 0.49 | 1.64 | 14.41 | 0.29 | |
KPG103A | 16.27 | 15.48 | 14.99 | 14.18 | 0.79 | 2.10 | 15.66 | 0.61 | |
KPG103B | 15.12 | 14.47 | 14.11 | 13.42 | 0.64 | 1.69 | 14.62 | 0.47 | |
KPG108A | 15.17 | 13.95 | 13.49 | 12.55 | 1.22 | 2.62 | 14.31 | 1.01 | |
KPG108B | 14.35 | 13.17 | 12.67 | 11.76 | 1.17 | 2.59 | 13.45 | 0.95 | |
KPG112A | 13.24 | 12.41 | 11.85 | 11.19 | 0.83 | 2.05 | 12.33 | 0.60 | CP |
KPG112B | 13.47 | 12.63 | 12.05 | 11.35 | 0.84 | 2.12 | 12.85 | 0.68 | CP |
KPG112s | 12.55 | 11.78 | 11.20 | 10.52 | 0.77 | 2.03 | |||
KPG125A | 13.65 | 12.88 | 12.21 | 11.39 | 0.77 | 2.26 | 13.16 | 0.63 | |
KPG125B | 12.92 | 12.15 | 11.56 | 10.81 | 0.77 | 2.11 | 12.42 | 0.63 | |
KPG136A | 14.98 | 14.29 | 13.72 | 13.31 | 0.69 | 1.67 | 14.73 | 0.58 | |
KPG136B | 15.21 | 14.34 | 13.73 | 13.24 | 0.87 | 1.97 | 14.87 | 0.75 | |
KPG141A | 15.21 | 13.96 | 13.40 | 12.65 | 1.25 | 2.56 | 14.49 | 1.06 | |
KPG141B | 14.97 | 13.92 | 13.50 | 12.67 | 1.05 | 2.30 | 14.62 | 0.95 | |
KPG150A | 14.24 | 13.26 | 12.46 | 11.90 | 0.98 | 2.34 | 13.84 | 0.86 | BS |
KPG150B | 13.28 | 12.23 | 11.57 | 10.85 | 1.05 | 2.43 | 12.80 | 0.95 | BS |
KPG151A | 15.40 | 14.17 | 13.42 | 12.77 | 1.22 | 2.63 | 14.32 | 0.93 | CP |
KPG151B | 15.07 | 13.87 | 13.13 | 12.53 | 1.20 | 2.53 | 14.60 | 1.05 | CP |
KPG151s | 14.67 | 13.33 | 12.55 | 11.94 | 1.34 | 2.73 | |||
KPG156A | 13.02 | 12.60 | 12.11 | 11.71 | 0.42 | 1.31 | 12.61 | 0.30 | CP |
KPG156B | 14.54 | 13.93 | 13.42 | 12.95 | 0.61 | 1.59 | 14.26 | 0.52 | CP |
KPG159A | 16.39 | 15.89 | 15.39 | 15.45 | 0.50 | 0.94 | 15.90 | 0.36 | |
KPG159B | 14.61 | 13.88 | 13.34 | 12.95 | 0.73 | 1.66 | 14.16 | 0.60 | |
KPG160A | 13.98 | 13.09 | 12.58 | 11.74 | 0.89 | 2.23 | 13.80 | 0.83 | |
KPG160B | 15.44 | 14.57 | 14.07 | 13.23 | 0.87 | 2.22 | 14.83 | 0.71 | |
KPG168A | 12.80 | 11.82 | 11.21 | 10.68 | 0.99 | 2.12 | 12.29 | 0.86 | CP |
KPG168B | 15.16 | 14.23 | 13.73 | 13.25 | 0.93 | 1.91 | 14.49 | 0.77 | CP |
KPG195A | 13.24 | 12.38 | 11.81 | 11.20 | 0.87 | 2.04 | 12.87 | 0.77 | |
KPG195B | 14.42 | 13.71 | 13.28 | 12.78 | 0.71 | 1.64 | 13.88 | 0.58 | |
KPG211A | 13.68 | 12.69 | 12.01 | 11.43 | 0.99 | 2.25 | 13.45 | 0.91 | |
KPG211B | 15.75 | 14.70 | 13.99 | 13.39 | 1.05 | 2.36 | 15.05 | 0.87 | |
KPG216A | BS | ||||||||
KPG216B | 13.28 | 12.70 | 12.37 | 11.67 | 0.58 | 1.62 | 12.88 | 0.36 | BS |
KPG249A | 12.45 | 12.10 | 11.67 | 11.42 | 0.35 | 1.03 | 12.26 | 0.30 | CP |
KPG249B | 12.93 | 12.50 | 12.01 | 11.68 | 0.43 | 1.24 | 12.51 | 0.32 | CP |
KPG249s | 11.89 | 11.49 | 11.03 | 10.75 | 0.40 | 1.14 | |||
KPG295A | 13.45 | 12.59 | 11.97 | 11.42 | 0.86 | 2.03 | 13.23 | 0.79 | CP |
KPG295B | 13.30 | 12.50 | 11.92 | 11.34 | 0.80 | 1.97 | 12.86 | 0.69 | CP |
KPG302A | 11.23 | 10.67 | 10.28 | 9.64 | 0.56 | 1.59 | 11.03 | 0.51 | |
KPG302B | 14.05 | 13.57 | 13.18 | 12.56 | 0.46 | 1.47 | 13.90 | 0.42 | |
KPG313A | 13.17 | 12.52 | 12.10 | 11.87 | 0.64 | 1.30 | 13.09 | 0.62 | |
KPG313B | 13.26 | 12.17 | 11.39 | 10.68 | 1.09 | 2.57 | 12.97 | 1.02 | |
KPG332A | 12.19 | 11.35 | 10.97 | 10.14 | 0.84 | 2.05 | 11.91 | 0.77 | |
KPG332B | 12.71 | 11.61 | 11.11 | 10.09 | 1.10 | 2.62 | 12.04 | 0.94 | |
KPG347A | 12.13 | 11.34 | 10.85 | 10.26 | 0.79 | 1.87 | 11.97 | 0.74 | CP |
KPG347B | 12.11 | 11.19 | 10.61 | 9.96 | 0.92 | 2.15 | 11.80 | 0.83 | CP |
KPG347s | 11.40 | 10.52 | 9.96 | 9.39 | 0.89 | 2.02 | |||
KPG389A | 13.69 | 12.99 | 12.37 | 12.15 | 0.71 | 1.55 | 13.40 | 0.61 | CP |
KPG | B | V | R | I | B-V | B-I |
![]() |
![]() |
|
KPG389B | 13.67 | 12.83 | 12.23 | 11.62 | 0.84 | 2.06 | 13.47 | 0.76 | CP |
KPG396A | 14.78 | 14.26 | 13.84 | 13.17 | 0.52 | 1.61 | 14.18 | 0.35 | |
KPG396B | 14.06 | 13.65 | 13.28 | 12.48 | 0.41 | 1.57 | 13.99 | 0.36 | |
KPG404A | 13.84 | 13.12 | 12.60 | 12.08 | 0.72 | 1.76 | 13.61 | 0.65 | CP |
KPG404B | 12.57 | 11.81 | 11.26 | 10.63 | 0.76 | 1.93 | 12.33 | 0.68 | CP |
KPG426A | 14.77 | 13.78 | 13.14 | 12.57 | 0.99 | 2.20 | 14.46 | 0.88 | |
KPG426B | 15.01 | 14.11 | 13.50 | 13.02 | 0.90 | 1.99 | 14.84 | 0.82 | |
KPG440A | 13.22 | 12.94 | 12.63 | 12.81 | 0.28 | 0.41 | 13.01 | 0.22 | |
KPG440B | 12.42 | 11.34 | 10.87 | 9.90 | 1.08 | 2.52 | 11.79 | 0.92 | |
KPG455A | 13.99 | 13.11 | 12.61 | 11.80 | 0.88 | 2.19 | 13.66 | 0.78 | |
KPG455B | 13.10 | 12.47 | 12.02 | 11.17 | 0.63 | 1.93 | 12.61 | 0.50 |
CP = Pair apparently in Contact.
BS = Bright Star nearby in the Field.
![]() |
Figure 3: Comparison between our CCD data and available CCD data from various authors for (S+S) galaxies. |
Open with DEXTER |
The next step involves comparison of our CCD magnitudes with other CCD measures in the four colour bands. Figure 3 shows the comparison with filled symbols denoting CCD measurements in the Cousins system, primarily from Han (1992); Reshetnikov (1993); and Laurikainen et al. (1998). Open symbols denote CCD measurements in the Johnson system, mainly Godwin et al. (1977); Doroshenko & Terebizh (1979); de Vaucouleurs & Longo (1988) and Márquez & Moles (1996). Metcalfe et al. (1998) reports B and V band photometry in the Landolt system while R and I are in the Cousins system. Giovanelli et al. (1997) report I-band data from a combination of sources. No attempt has been made to transform from any of the above photometric systems to Cousins system.
Notice that in Fig. 3 there seems to be no clear systematic tendency between the compared data, in spite of the small number of galaxies in common. The sigma values obtained through a comparison (only) in the Cousins systems are 0.25, 0.25, 0.20 and 0.30 in B, V, R and I respectively. However, it is fair to mention that this is not a straightforward comparison, since we are also comparing both intrinsic and extrinsic differences involved in each photometric system as well as differences in the reduction procedures, that are more easily detected at fainter magnitudes.
Finally, for most paired galaxies, more than one long exposure
per filter is available. Thus we evaluate in addition, the
internal accuracy of our photometry by comparing the total
magnitudes derived from the individual exposures. We find rms
differences between individual measurements of
,
,
and
.
Additionally, by estimating total magnitudes for all
galaxies before and after sky subtraction, typical values
,
,
and
are obtained. In the
Appendix, we report additional estimations of magnitudes at
three concentric circular apertures for all the paired galaxies
in this study.
The estimated magnitudes and colours of the galaxies in
the sample are presented in Table 3.
Entries are as follows: Col. (1) gives the identification
in Karachentsev Catalogue, Cols. (2) to (5) give the
observed total integrated magnitudes in B, V, R and
I bands, Cols. (6) and (7) give the observed (B-V) and
(B-I) colour indices. Finally Cols. (8) and (9) give
the total corrected
magnitude and
colour index in the RC3 system. LogR25 and the galactic
absorption AB were taken from RC3 Catalogue and
Burstein & Heiles (1982), respectively.
As stated above, total typical uncertainties in our photometry
are 0.15, 0.14, 0.15 and 0.14 for B, V, R and I bands.
Magnitude and colour corrections were not applied for
a few small galaxies (blank spaces in Table) in the neighborhood
of our pairs, due to a lack of reliable information.
Our observations span a range (11, 15.9) and (0.3, 1.1) mag
in
and
,
respectively. The
observed (B-V) range is comparable (by judging the
colour maps scales) to that in a similarly selected sample
of pairs in the southern hemisphere by Reduzzi & Rampazzo
(1996), although some E/S0 components were
included in that sample. Interestingly, our
range is comparable to the full range found in Larson & Tinsley
(1978) in spite of the fact that their
interacting sample is biased in favour of strongly peculiar
systems from the Arp's catalogue. Similarly, the photoelectric
Cousins UBVRI photometry of interacting galaxies by Johansson
& Bergvall (1990) shows a
comparable range in the observed (B-V) colours, although
this sample is biased in favour of disturbed morphology,
the presence of bridges and includes a fraction of E/S0
components.
As a byproduct of his famous photometric survey of nearby
galaxies, Holmberg (1958) compared the
photographic colours of paired galaxies and found a significant
correlation between the colours of pair components. This
phenomenon has since been referred to as the "Holmberg effect''.
Figure 4 shows the correlation between the
colour index. In a few cases irregular
galaxies belonging to pairs have conventionally been considered
as spirals. The colour index along the vertical axis refers to
the brighter (primary) component and that along the horizontal
axis refers to the fainter (secondary) component in each pair.
To reinforce the validity of any correlation, other symbols
indicate sources of
data for additional (S+S)
Karachentsev pairs from the literature.
![]() |
Figure 4:
The Holmberg effect.
![]() ![]() |
Open with DEXTER |
The colour correlation between pair components
is tight. A correlation coefficient
with a
residual sigma of 0.18 is obtained for our (S+S) data.
Additionally, a fitting to all the data in Fig. 4,
give a correlation coefficient
with a residual sigma
of 0.18. All the (S+S) pairs with (B-V) either
from our observations or from the literature, have a median
relative velocity,
km s-1 and a median
projected separation
kpc.
Although the physical explanation of the Holmberg effect
is complex, it has been interpreted as reflecting a
tendency for similar types of galaxies to form together
(morphological concordance), a possible reflection of the
role of local environment in determining galaxy morphology,
but alternatively, it can presumably also reflect mutually
induced star formation (Kennicutt et al.
1987) in physical pairs.
To discuss the optical morphology (that could be modified by the presence of bars, spiral arms, rings, etc.) and its relationship to the global photometrical properties, the final results for each pair are presented in the form of a mosaic (Fig. A.1) including: 1) mean azimuthally averaged surface brightness and colour profiles, 2) gray scale B-band images, 3) (B-I) colour index maps and 4) B band-filtered images for each pair. In most of the cases, not all the foreground stars in each field have been removed. The images in the lower panels 3) and 4) can be combined to look for morphological features like the presence of bars, rings, the shape of spiral arms, the presence of tidal features and other morphological distortions presumably associated with the interactions. The filtered/enhancing techniques (Sofue 1993 applied in 4), allow the subtraction of the diffuse background in a convenient way to discuss different morphological details.
Karachentsev (1972) identified three basic interaction classes (AT, LI and DI) that describe the pairs which show obvious signs of interaction. AT class identifies pairs with components in a common luminous halo with a symmetric, amorphous or shredded, asymmetric (sh) structure. LI pairs show evidence of tidal bridges (br), tails (ta) or both (br+ta). DI pairs show evidence of structural distortion in one (1) or both (2) components. We add to this sequence NI for the (S+S) pairs with no obvious morphological distortion. The order AT-LI-DI-NI can be regarded as a sequence from strongest to weakest evidence for tidal distortion or, alternatively, most to least dynamically evolved (interpreting a common envelope as a sign of extensive dynamical evolution in pairs).
Based on our CCD observations, it is now possible to attempt 1) a reclassification of the Hubble morphology from a combination of our colour index (B-I) maps and sharp/filtered B images, 2) a reclassification of the global pair interaction morphology (I/A class hereafter) in the Karachentsev Catalogue and 3) a reclassification of the spiral arm morphology as suggested by Elmegreen & Elmegreen (1982) (hereafter EE class).
It is known that the colours of spiral galaxies are correlated with its morphological type T. Although the colour indices of galaxies belonging to type T will have a large dispersion, the median value declines systematically as T increases along the morphological sequence. Median integrated total (B-V) colours of galaxies according to morphological class are given by Roberts & Haynes (1994). The UGC and the Local Supercluster (LSc) samples in Roberts & Haynes (1994) are rather inhomogeneous in terms of environment, but the interacting objects were excluded from their analysis. We may consider these samples as comparison/reference samples for the following discussion.
Before proceeding to a discussion of the results shown in tables and figures, we present comments on morphological details found in individual pairs that may be relevant to our conclusions and look for any relationship to the global photometrical profiles.
KPG64A. The galaxy is classified as SA(s)b pec.
Our (B-I) colour map shows two centrally symmetric spiral
arms that become bifurcated at the outer parts. The arms
are sharp-defined and the B-band sharp/filtered image can
show some well-defined knotty structures along them. A bright
small nucleus can also be appreciated. We classify this
galaxy as Sc pec. The type of arms shown may probably be
produced/modified by the interaction as predicted by
simulations in Noguchi (1990). The total
colour is representative of
Sab-Sb types. Our EE class is 6.
KPG64B. The galaxy is classified as SB(s)a pec.
Our (B-I) colour map shows an apparently inclined
galaxy that could be simulating a barred structure in the
central region of a lower resolution image. The outer spiral
structure resembles an integral sign that could be tidally
generated by the interaction, on line with simulations
by Noguchi (1990). The sharp/filtered image shows
a faint bifurcated structure emanating from the eastern arm.
There is also evidence of knotty structure along the arms,
but no clear evidence of a bar structure. We classify this
galaxy as Sbc. The total
colour is more
representative of S0a-Sa types. We notice that the colour
profiles tend to be flat after 15
.
Our EE class
is 6. The I/A class for the pair is LI.
KPG68A. This galaxy is overlapping at the southeast
with its companion. Our iterative modeling of the light
distribution is poor and caution is needed with the total
magnitudes and colours for both galaxies. The galaxy is
classified as a Scd:. Our sharp/filtered and B-I colour
map images shows a bright nucleus plus multiple arms with
knotty structure along them. The total
colour is representative of Sb-Sbc types. Our EE class
is 3.
KPG68B. This galaxy is overlapping at the north
with its companion. The galaxy is classified as a SBb:. Our
sharp/filtered and B-I colour map images shows knotty structure
along the arms from either end of a prominent bar. The total
colour is representative of Sb-Sbc types.
The colour profiles in this barred galaxy are flat after
5
from its center. The I/A class for the pair is
DI. Our EE class is 10.
KPG75A. The galaxy is classified as E?, but our (B-I)and sharp/filtered images show a bright central nucleus from
which two opened and diffuse spiral arms emanate. The spiral
pattern shows an integral sign (perhaps as a by product of
the interaction). We classify this galaxy as Sab. The
colour is representative of S0a-Sa types.
KPG75B. The galaxy is classified as SB?, and our (B-I)and sharp/filtered images show a bright nucleus and two
wrapped adjacent spiral arms that in projection may
simulate a bar. We cannot clearly identify a bar
structure. The arm at the north appears warped.
We classify this galaxy as Sb. The
colour is representative of Sab-Sb types. The I/A class
for the pair is DI. Our EE class is 7.
KPG88A. The galaxy is classified as a SA(s)c
and our (B-I) and sharp/filtered images shows a few
bright knots along multiple arms that emanate from a
bright nucleus. The
colour is
redder than that corresponding to its
morphological type. Our estimated (B-V) colour is
consistent, however, with that reported by Prugniel
& Héraudeau (1998). The colour
profiles tend to be flat after 15
.
Our EE
class is 12.
KPG88B. The galaxy is classified as a SBcd:. Both our
sharp/filtered and (B-I) colour map show a prominent bar
and complex arms extending from either end. The
colour is redder than that corresponding to
its morphological type. The I/A class for the pair is DI.
Our EE class is 10.
KPG98A. The galaxy is classified as Scd:. Our (B-I) and
sharp/filtered images show a bright nucleus plus a perturbed
spiral pattern that seems warped in projection. A few knots
can be seen along the arms. The
colour
is bluer than that corresponding to its morphological
type. We caution the reader about an aparent inconsistency
in the results obtained for this pair. Contrary to the
observed (B-V) value, the corresponding colour profiles
show a tendency to be redder. After repeating the calculations
and taking into account our estimated errors in B and V
magnitudes, we do not have an explantion for this behaviour.
Our EE class is 2.
KPG98B. This galaxy is classified as S?. Our (B-I)and sharp/filtered images show a prominent nucleus plus a faint
but defined spiral pattern that simulates an outer
pseudo-ring structure. This pattern could be reminiscent of
the interaction with its companion. We classify this galaxy
as (R)Sa. The
colour is redder than
that corresponding to its morphological type. RC3 Catalogue
reports (only) a blue photographic magnitude with an error
of 0.2 mag that was transformed to the standard system.
However, this value is within 0.2 mag to ours.
The I/A class for the pair is DI.
KPG102A. This galaxy is classified as Sa. Our (B-I)
and sharp/filtered images show a prominent nuclear
structure from which a diffuse wrapped spiral
pattern emerges. We classify the galaxy as SBab. The
colour is bluer than that corresponding
to its morphological type.
KPG102B. The galaxy is classified as Sb and our
(B-I) and sharp/filtered images show a bright
nuclear region plus a beautiful symmetric and
sharply-defined spiral pattern that could be caused by
the interaction with its companion. We classify the
galaxy as Sc. The
colour is bluer than
that corresponding to its morphological type. The
(B-R) and (B-I) colour profiles have a tendency to
be flat after 10
.
The I/A class for the pair
is LI. Our EE class is 11.
KPG103A. The galaxy is classified as Sb. Its
small angular size make the visualization of features a
difficult task. At our resolution, both the (B-I) and
sharp/filtered images shows a peculiar morphology. Keel
(1988) has extensively studied this galaxy. The
colour is representative of a Sab-Sb
galaxy. The (B-V) colour profile have a tendency to be
flat along the observed radius.
KPG103B. The galaxy is classified as Sa.
At our resolution, the (B-I), sharp/filtered
and unsharp masking images show a peculiar morphology.
The arms appear radially distributed from a prominent
bulge. Keel (1988) has extensively studied
this galaxy. The
colour is representative
of a Scd-Sd galaxy. The I/A class for the pair is DI.
KPG108A. The galaxy is classified as Sbc. Our (B-I)
and sharp/filtered images show a highly inclined galaxy with
a bright elongated bulge and a complex dusty structure.
It is difficult to find definite signs of perturbation.
The
colour is redder than that
corresponding to its morphological type. RC3 Catalogue
reports (only) a blue photographic magnitude with an error
of 0.2 mag that was transformed to the standard system.
However, this value is within 0.2 mag to ours.
The (B-R) and (B-V) colour profiles have a tendency to
be flat after 25
.
KPG108B. The galaxy is classified as Sb. Our (B-I)
and sharp/filtered images show a highly inclined galaxy with
a complex dusty structure. It is difficult to trace
signs of perturbation. A small galaxy (north-east) in its
neighborhood can be appreciated. The
colour
is redder than that corresponding to its morphological type.
RC3 Catalogue reports (only) a blue photographic magnitude with
an error of 0.2 mag that was transformed to the standard
system. However, this value is within 0.2 mag to ours.
The colour profiles have a tendency to be flat after 30
.
The I/A class for the pair is NI.
KPG112A. The galaxy is classified as S0/a.
Our sharp/filtered and B-I images show and edge-on
galaxy resembling a lenticular or an early-type spiral
with a distorted disk. The distorted disk may be representing
a tidal tail/counter-tail structure generated by the interaction.
We classify this galaxy as Sa. The
colour is
representative of Sab-Sb types. The (B-V) and (B-R) colour
profiles tend to be flat after 10
,
while the (B-I)
colour profile appear flat all along the observed radius.
KPG112B. The galaxy is classified as S0:. Our
sharp/filtered and B-I images show a bright prominent
bulge. Two diffuse spiral arms appear wrapped. The arms
at the west side are seen, in projection, overlapping at
the eastern arm of its companion galaxy. We classify this
galaxy as Sa. The
colour is
representative of a Sa galaxy. Our EE class is 12.
The I/A class for the pair is LI.
KPG125A. The galaxy is classified as Pec. In spite
of its small angular size, our (B-I) and sharp/filtered
images show two faint spiral arms emerging from a complex and
bright central region. We classify this galaxy as Sab pec.
The estimated
colour is representative of
Sab-Sb types. The colour profiles in this galaxy show a
tendency to be flat after 5
.
KPG125B. The galaxy is classified as S pec. However,
both our (B-I) and sharp/filtered images show multiple
and complex spiral arms with knotty features along them and
emanating from a bright nuclear region. We classify
this galaxy as Sc pec. The estimated
colour
is representative of Sab-Sb types. The colour profiles
show a tendency to be flat after 20
.
The
I/A class for the pair is DI. Our EE class is 9.
KPG136A. This galaxy is classified as S?. Our (B-I) and
sharp/filtered images show a bright central region from which
multiple but diffuse arms appear to emanate. We classify this
galaxy as Sbc. The estimated
colour is
representative of Sbc-Sc types. Our EE class is 10.
KPG136B. This galaxy is classified as S?. Our (B-I) and
sharp/filtered images show a bright nuclear region surrounded by
a tightly wrapped arm-like structure resembling a ring or
pseudo-ring. An outer faint feature also resembles a diffuse
shell/arc that may be associated with a tidal origin. We classify
the galaxy as S(r)ab. The
colour is representative
of a Sa type. The I/A class for the pair is DI. Our EE class is 8.
KPG141A. The galaxy is classified as S?. Our (B-I)
and sharp/filtered images show a highly inclined galaxy where
a central bulge and a few knots along a thin linear feature
(arm seen in projection?) at the north-east can be appreciated.
We classify this galaxy as Sbc. The
colour is
redder than that representative of its morphological
type. RC3 Catalogue reports (only) a blue photographic magnitude
with an error of 0.3 mag that was transformed to the standard
system. However, this value is within 1.1 mag of ours.
KPG141B. The galaxy is classified as S?. Our (B-I) and
sharp/filtered images show a bright prominent central region
and two wrapped but defined arms. We classify this galaxy as Sb.
The estimated
colour is redder than
that representative of its morphological type. RC3 Catalogue
reports (only) a blue photographic magnitude with an error
of 0.3 mag that was transformed to the standard system.
However, this value is within 0.3 mag to ours. The I/A class
for the pair is DI. Our EE class is 7.
KPG150A. The galaxy is classified as Sa. Our (B-I)
and sharp/filtered images show an internal two-arm spiral
pattern and a bright nucleus. An outer spiral arm pattern is
wrapped and may be resembling, in projection, a pseudo-ring.
We classify this galaxy as SA(r)b. The estimated
colour is representative of S0-S0a types. Our EE class is 7.
KPG150B. The galaxy is classified as SBb.
Our (B-I) and sharp/filtered images show a sharply defined
bar and multiple knotty arms wrapped enough in the central
region to resemble an internal ring. We classify this galaxy as
SB(r)c. The colour profiles (in the presence of a bright nearby
field star) do not show a tendency to be flat like other
barred galaxies in this sample. The estimated
colour is redder than that representative of its morphological
type. Prugniel & Héraudeau (1998) report a blue magnitude
in agreement (for a similar aperture) to ours. RC3 Catalogue
reports (only) a blue total magnitude with an error of 0.15 mag that was transformed to the standard system. However,
this value is within 0.2 mag to ours. The I/A class for the
pair is NI. Our EE class is 8.
KPG151A. The galaxy is seen slightly overlapping,
in projection, to its companion galaxy at the south-east.
The galaxy is classified as Sc. Our (B-I) and sharp/filtered
images show an edge-on galaxy with a clearly defined bulge
region. The estimated
colour is redder
than that corresponding to its morphological type. We
could not find a reference in the literature with which to compare
magnitudes and colours for this source.
KPG151B. The galaxy is classified as SB?. Our (B-I)
and sharp/filtered images show a bright prominent nuclear
region and an adjacent elongated feature that resembles
a bar. We classify this galaxy as SBb. The
colour is redder than that corresponding to its
morphological type. RC3 Catalogue reports (only) a blue
photographic magnitude with an error of 0.2 mag that was
transformed to the standard system. However, this value
is within 0.1 mag of ours. The (B-V) colour profile shows a
marginal tendency to be flat after 20
.
The I/A class
for the pair is LI. Our EE class is 8.
KPG156A. The galaxy is classified as SA(r)c pec. Our
sharp/filtered and (B-I) images show a bright central nucleus
surrounded by two knotty arms forming an inner ring structure.
The arms extend far from the center forming: 1) a bridge to its
companion and 2) a very long tail. They may be tidally-generated
by the interaction. In addition, faint filamentary structures
are seen almost tangent to the ring. The estimated
colour is definitely bluer than that corresponding to its
morphological type. Our EE class is 11.
KPG156B. The galaxy is classified as SB(rs)c pec.
However, in our sharp/filtered and (B-I) images no clear
ringed structure is noticed. We notice instead,
a bright and somehow elongated nuclear region with two
diffuse and opened spiral arms resembling a integral sign.
We classify this galaxy as SBbc pec. The estimated
colour is representative of Sbc-Sc types. The (B-R) and
(B-I) colour profiles show a tendency to be flat after
15
.
The I/A class for the pair is LI.
KPG159A. The galaxy is classified as Sb. The small
angular size of this galaxy does not allow both the
sharp/filtered and (B-I) images to show any detailed
morphology. The
colour is representative of
Sm-Im types.
KPG159B. The galaxy is classified as Sb. The sharp/filtered
and (B-I) images shows an inclined galaxy with a bright
nuclear region and wrapped spiral arms. A faint linear feature
crossing the central region resembles a bar. We classify this
galaxy as SBb. The
colour is representative
of Sb-Sbc types. The I/A class for the pair is DI.
KPG160A. The galaxy is classified as SB(s)a. Our
(B-I) and sharp/filtered images show a bright outer
ring enclosing a bar-like feature. The outer ring is
bluer than the adjacent disk. We classify this galaxy as
(R')SB(s)a. The
colour is representative
of S0a-Sa types. The colour profiles show a tendency to
be flat after 25
.
Our EE class is 8.
KPG160B. The galaxy is classified as SBa. Our
(B-I) and sharp/filtered images show a highly
inclined system where it is difficult to see the bar
and bulge regions. There is knotty structure along the
main body of the galaxy. We classify this galaxy as Sb.
The
colour is representative of Sa-Sab
types. If the outer ring in the companion galaxy is regarded
as evidence of interaction, the I/A class for the pair is DI,
otherwise is NI.
KPG168A. The galaxy is classified as Sa.
Our (B-I) and sharp/filtered images show a prominent bulge
region and two symmetric spiral arms that simulate a
pseudo-ring. In the external parts, the arms are extended
and diffuse (resembling an integral sign) forming a bridge to
the south-east of its companion galaxy. We classify this galaxy
as S(s)b. The
colour is more representative of
S0-S0a types. The colour profiles show a tendency to be flat
from 40
.
Our EE class is 6.
KPG168B. The galaxy is classified as Sc. Our (B-I) and
sharp/filtered images show an apparently inclined system with a
few prominent knots along the main body. Two adjacent diffuse arms
are also appreciated. One of them is apparently forming a
bridge at the west of its companion galaxy. The
colour is more representative of Sa-Sab types. The colour profiles
show a tendency to be flat along most of the observed radius.
The I/A class for the pair is LI.
KPG195A. The galaxy is classified as SB(s)a pec.
The configuration of this pair resembles that of KPG168. Our
(B-I) and sharp/filtered images show a prominent bulge
and an adjacent linear feature that crosses the central region
resembling a bar. From this bar, two spiral arms emerge. These
arms are prominent in the central regions and become diffuse
and extended (resembling an integral sign) at the external
parts. We classify this galaxy as SB(s)b pec. The
colour is representative of S0a-Sa types The colour profiles
show a marginal tendency to be flat after 40
.
Our
EE class is 6.
KPG195B. The galaxy is classified as SB(s)m? Our
(B-I) and sharp/filtered images show an apparently inclined
system with bright condensations along the main body and two
adjacent arms that become diffuse at the outskirts.
The bar structure is difficult to discerne. We classify this
galaxy as Sc. The
colour is representative of
Sbc-Sc types. The I/A class for the pair is DI.
KPG211A. The galaxy is classified as (R')SAB(rs)ab pec:
and our (B-I) and sharp/filtered images seem to confirm this
classification. The pattern of spiral arms is complex, tightly
wrapped and shows blue colours. This could be a sign of strong
perturbation from its companion. The estimated
is
representative of S0-S0a types. The colour profiles show a
tendency to be flat after 30
.
Our EE class is 8.
KPG211B. The galaxy is classified as Sb: and our (B-I)
and sharp/filtered images show an apparently inclined galaxy
with a prominent bulge and two symmetric, diffuse spiral arms.
We classify this galaxy as Sa. The
colour is
representative of S0-S0a types. Our EE class is 7. The I/A class
for the pair is DI.
KPG216A. The galaxy has a bright nearby field star that was difficult to subtract in our iterative procedure. The galaxy is classified as SB(s)b pec: Our (B-I) and sharp/filtered images show an elongated central region resembling a bar structure from which two diffuse spiral arms (integral sign) emerge. Our EE class is 10.
KPG216B. The galaxy is classified as SAB(s)c pec: Our
(B-I) and sharp/filtered images show an elongated feature
crossing the center and resembling a bar from which two
knotty arms emanate. The arm at the west is multiple.
We classify this galaxy as SBc pec. The
colour
is representative of Sm-Im types. The colour profiles show
structure and a global tendency to be flat after 35
.
The I/A class for the pair is DI. Our EE class is 9.
KPG249A. The pair show an apparent low degree of overlapping.
The galaxy is classified as SAB(rs)cd pec. Our sharp/filtered
and (B-I) images show two bright condensations in the nuclear
region. The arms show a bifurcated spiral pattern and knotty
features. The arm at north-east is forming an apparent bridge to
its companion galaxy. We classify this galaxy as SABcd pec. The
colour is more representative of Sm-Im types.
The colour profiles show a tendency to be flat after 30
.
Our EE class is 6.
KPG249B. The galaxy is classified as IBm pec. Our
sharp/filtered and (B-I) images show some bright
condensations along a main elongated body that resembles
a bar structure from which two diffuse opened arms emerge.
We classify this galaxy as SBm pec. The
colour
is more representative of Sm-Im types. The colour profiles show
a tendency to be flat along the observed radius. The I/A class
for the pair is LI.
KPG295A. This is a low-degree overlapping pair where
both components show remarkably similar morphological
features. The galaxy is classified as SAB(rs)a pec and both
our (B-I) and sharp/filtered images show a bright nuclear
region and a faint adjacent broad feature that may be resembling
a bar structure. These features are enclosed by an internal
set of blue arms forming an elongated internal ring.
In addition, this galaxy also shows an external diffuse and
elongated ring. We classify this galaxy as (R')SAB(r)a pec.
The
colour is representative of S0a-Sa types.
Our EE class is 8.
KPG295B. The galaxy is classified as SAB(rs)ab pec. Our
(B-I) and sharp/filtered images show a galaxy with a prominent
nuclear region enclosed by two wrapped arms resembling an inner
ring structure. The external arms are bright, blue and
wrapped. The
colour is representative of
Sab-Sb types. The I/A class for the pair is DI. Our EE class
is 8.
KPG302A. The galaxy is classified as SAB(rs)c:. Our (B-I)
and sharp/filtered images show a beautiful spiral structure with
knotty blue features all along the arms. We cannot identify
signs of a barred structure. We classify this galaxy as Sc. The
colour is representative of Sc-Scd types. Our EE
class is 12.
KPG302B. The galaxy is classified as SB0/a pec. Our
(B-I) and sharp/filtered show a prominent and elongated
central region that may resemble a bar. Alternatively,
we may interpret that as two overlapping bright central
sources forming an elongated feature from which two
diffuse spiral arms emanate. The arm towards the companion
is apparently bifurcated forming an external arc/shell-like
feature. We classify this galaxy as SBbc pec. The
colour is representative of Sd-Sm types. The colour profiles
show a tendency to be flat all along its radius.
The I/A class for the pair is DI. Our EE class is 6.
KPG313A. The galaxy is classified as
SAB(rs)cd. Our (B-I) and sharp/filtered images show a
central elongated bar-like feature that is enclosed by a set
of arms with apparently differing pitch angles and resembling
a broken ring. Blue knotty features are observed along the
arms. The
colour is representative of Sb-Sbc
types. The (B-I) colour profile show a tendency to be flat
after 40
.
Our EE class is 1.
KPG313B. The galaxy is classified as Sab:sp. Our
sharp/filtered and (B-I) images show an inclined galaxy
with extended and apparently warped arms. The
colour is redder than that corresponding to its morphological
type. RC3 reports total asymptotic B and V magnitudes
with associated errors of 0.15 mag that imply a (B-V) colour
in agreement to our observed value. The I/A class for the pair
is DI.
KPG332A. The galaxy is classified as SA(rs)c and our (B-I)
and sharp/filtered images show a bright nucleus and blue knotty
arms. We do not find evidence for an internal ring or s-shaped
structure. We classify this galaxy as Sc. The
colour is representative of Sa type. Our EE class is 3.
KPG332B. The galaxy is classified as Sc: sp
and our (B-I) and sharp/filtered images show a spectacular
and complex dust lane structure all along the plane of the
galaxy. The
colour is redder than
that corresponding to its morphological type. RC3 reports
total asymptotic B and V magnitudes with associated errors
of 0.1 mag that imply a (B-V) colour in agreement with our
observed value. The I/A class for the pair is NI.
KPG347A. The components in this pair show an
apparent overlapping but similar morphological types.
The galaxy is classified as SA(rs)bc. Our sharp/filtered and
(B-I) images show a prominent bulge region and wrapped
spiral arms that resemble an inner ring. Blue knotty
features are seen along the arms. We classify this galaxy
as SA(r)bc. The
colour is representative of Sa
types. Our EE class is 12.
KPG347B. The galaxy is classified as SA(rs)bc. Our
sharp/filtered and (B-I) images show an inclined galaxy with
a bright nucleus and knotty features along multiple spiral
arms. We classify this galaxy as Sc. The estimated
colour is representative of Sa types. The
I/A class for the pair is DI. Our EE class is 3.
KPG389A. The components in this pair have similar
morphological features (cf. KPG295) and their arms overlap
in the outer region. The galaxy is classified as SAB(s)b pec
and our (B-I) and sharp/filtered images show a very definite
nucleus and an adjacent small spiral arm enclosed
by two external arms. They are knotty and resemble an inner
pseudo-ring but become diffuse at large radii. The east arm
is seen interpenetrating the west arm of its companion
such that an x-like feature is formed. We classify this
galaxy as SA(rs)bpec. The
colour is
representative of Sb-Sbc types. Our EE class is 6.
KPG389B. The galaxy is classified as SA(s)b: pec and
our (B-I) and sharp/filtered images show an elongated nuclear
region from which two long and diffuse arms emerge. The west arm
appears crossing the east arm of its companion forming an x-shaped
feature. We classify this galaxy as SABb pec. The
colour is representative of Sa-Sab types. The colour profiles
show a tendency to be flat after 20
.
The I/A class for
the pair is LI. Our EE class is 7.
KPG396A. The galaxy is classified as SB(s)d: sp. Our
(B-I) and sharp/filtered images show an apparently inclined
system with an elongated nucleus and a spiral pattern that
is difficult to trace. The
colour is more
representative of Sm-Im types.
KPG396B. The galaxy is classified as SB(s)d. Our (B-I)and sharp/filtered images show a prominent bar structure
and a complex, knotty spiral pattern with differing pitch
angles. The
colour is representative of a Sm-Im
types. The colour profiles show structure and a tendency to be
flat after 25
.
The I/A class for the pair is DI.
Our EE class is 1.
KPG404A. The pair show an apparent low degree of
overlapping. The galaxy is classified as SB(s)b pec.
Our sharp/filtered and (B-I) images show a prominent nucleus
and a faint adjacent linear bar from which
two spiral arms (integral sign tidal arms) emanate.
The arms are wrapped and simulate an inner ring structure.
A third small galaxy can be seen near the end of the
western arm (tail). The southern arm is seen forming a bridge
to its companion galaxy. We classify this galaxy as SB(r)b pec.
The
colour is representative of Sab-Sb types.
The colour profiles show a tendency to be flat after 25
.
Our EE class is 10.
KPG404B. The galaxy is classified as SA(s)b pec. Our
sharp/filtered and (B-I) images show a bright nucleus and
apparently strong dust lanes along the arms (see the arm
towards the companion galaxy). The
colour is
representative of Sab-Sb types. The I/A class for the pair is LI.
Our EE class is 11.
KPG426A. The galaxy is classified as S?. Our (B-I)
and sharp/filtered images show a prominent bulge and barred
structure. At either end of the bar, strong condensations
and two thin/faint and wrapped arms emanate. There is also
indication of a ring enclosing the bar. We classify this
galaxy as SB(r)b. The
colour is representative
of S0-S0a types. The colour profiles show a tendency to be flat
after 25
.
Our EE class is 10.
KPG426B. The galaxy is classified as S?. Our (B-I)
and sharp/filtered images show a prominent but elongated bulge
region and a very faint spiral pattern. An unsharp masking image
suggest that an arc-like structure may be present at the western
external part. We classify this galaxy as SABb. The
colour is representative of S0a-Sa types. The I/A class for the pair
is DI. Our EE class is 8.
KPG440A. The galaxy is classified as SAB(rs)d and our
(B-I) and sharp/filtered images show a bright central
bar and a multiple spiral pattern with knotty structure
all along the arms. We classify this galaxy as SBcd. The
colour is definitely bluer than that
corresponding to its morphological type. Our EE class is 6.
KPG440B. The galaxy is classified as SBc? and our
(B-I) and sharp/filtered images show a very complex dust
lane structure along the plane of the galaxy, similar to
KPG332b. In our images it is difficult to trace the nuclear
region, bulge or bar. The
colour is
representative of E-S0 types. The I/A class for the pair is NI.
KPG455A. The galaxy is classified as SB(s)b and our
(B-I) and sharp/filtered images show a bright nuclear
region and two faint wrapped spiral arms resembling an inner
ring. It is difficult to trace the presence of a bar, although
the bulge region is elongated. The spiral pattern becomes diffuse at
the outer parts. We classify this galaxy as SA(r)b. The
colour is representative of S0a-Sa types.
KPG455B. The galaxy is classified as SB(s)bc but our
(B-I) and sharp/filtered images show a bright nucleus from
which a spiral pattern emerge. A Blue knotty structure is observed
along the arms. At our resolution, we have no clear evidence of a
barred structure. We classify this galaxy as SA(s)bc. The
colour is representative of Sc-Scd types. The
I/A class for the pair is DI. Our EE class is 7.
Table 4 is a summary of the results found in this
work. Column (1) gives the pair catalogued number, Col. (2) gives
the Hubble Type as reported in NED, Col. (3) gives the Hubble Type
as estimated in this work, Col. (4) gives the
Elmegreen (EE) class, Col. (5) gives the revised Karachentsev
interaction I/A class, Col. (6) shows when a flat colour
profile is present, and finally Col. (7) remarks the presence
of Bars, Knots, Rings and Shell structures.
Galaxy pair | HUBBLE TYPE(NED) | HUBBLE TYPE(THIS WORK) | EE CLASS | I/A CLASS | PROFILE | NOTES |
KPG64A | SA(s)b pec | Sc pec | 6 | LI | K | |
KPG64B | SB(s)a pec | Sbc | 6 | F | K | |
KPG68A | Scd: | 3 | DI | K | ||
KPG68B | SBb: | 10 | F | B, K | ||
KPG75A | E? | Sab | DI | |||
KPG75B | SB? | Sb | 7 | |||
KPG88A | SA(s)c | 12 | DI | F | K | |
KPG88B | SBcd: | 10 | B | |||
KPG98A | Scd: | 2 | DI | F | K | |
KPG98B | S? | (R)Sa | R | |||
KPG102A | Sa | SBab | LI | B | ||
KPG102B | Sb | Sc | 11 | F | ||
KPG103A | Sc | DI | F | |||
KPG103B | Sa | |||||
KPG108A | Sbc | NI | F | |||
KPG108B | Sb | F | ||||
KPG112A | S0/a | Sa | LI | F | ||
KPG112B | S0: | Sa | 12 | |||
KPG125A | Pec | Sab pec | DI | F | ||
KPG125B | S pec | Sc pec | 9 | F | K | |
KPG136A | S? | Sbc | 10 | DI | ||
KPG136B | S? | S(r)ab | 8 | R | ||
KPG141A | S? | Sbc | DI | K | ||
KPG141B | S? | Sb | 7 | |||
KPG150A | Sa | S(r)b | 7 | NI | R | |
KPG150B | SBb | SB(r)c | 8 | B, K, R | ||
KPG151A | Sc | LI | ||||
KPG151B | SB? | SBb | 8 | F | B | |
KPG156A | SA(r)c pec | 11 | LI | K, R | ||
KPG156B | SB(rs)c pec | SBbc pec | F | B | ||
KPG159A | Sb | DI | ||||
KPG159B | Sb | SBb | B | |||
KPG160A | SB(s)a | (R')SB(s)a | 8 | DI | F | B, R |
KPG160B | SBa | Sb | K | |||
KPG168A | Sa | S(s)b | 6 | LI | F | R |
KPG168B | Sc | F | K | |||
KPG195A | SB(s)a pec | SB(s)b pec | 6 | DI | F | B |
KPG195B | SB(s)m? | Sc | K | |||
KPG211A | (R')SAB(rs)ab pec: | 8 | DI | F | B | |
KPG211B | Sb: | Sa | 7 | |||
KPG216A | SB(s)b pec: | 10 | DI | B | ||
KPG216B | SAB(s)c pec: | SBc pec | 9 | F | B | |
KPG249A | SAB(rs)cd pec | SABcd pec | 6 | LI | F | B, K |
KPG249B | IBm pec | SBm pec | F | B, K | ||
KPG295A | SAB(rs)a pec | (R')SAB(r)a pec | 8 | DI | B, R | |
KPG295B | SAB(rs)ab pec | 8 | B, R | |||
KPG302A | SAB(rs)c: | Sc | 12 | DI | K | |
KPG302B | SB0/a pec | SBbc pec | 6 | F | B | |
KPG313A | SAB(rs)cd | 1 | DI | F | B, R, K | |
KPG313B | Sab:sp | |||||
KPG332A | SA(rs)c | Sc | 3 | NI | K | |
KPG332B | Sc: sp | |||||
KPG347A | SA(rs)bc | 12 | DI | K | ||
KPG347B | SA(rs)bc | Sc | 3 | K | ||
KPG389A | SAB(s)b pec | SA(rs)b pec | 6 | LI | K | |
KPG389B | SA(s)b: pec | SABb pec | 7 | F | B | |
KPG396A | SB(s)d: sp | DI | B | |||
KPG396B | SB(s)d | 1 | F | B, K | ||
KPG404A | SB(s)b pec | SB(r)b pec | 10 | LI | F | B, R |
Galaxy pair | HUBBLE TYPE(NED) | HUBBLE TYPE(THIS WORK) | EE CLASS | I/A CLASS | PROFILE | NOTES |
KPG404B | SA(s)b pec | 11 | ||||
KPG426A | S? | SB(r)b | 10 | DI | F | B, R |
KPG426B | S? | SABb | 8 | B, Sh | ||
KPG440A | SAB(rs)d | SBcd | 6 | NI | B, K | |
KPG440B | SBc? | B | ||||
KPG455A | SB(s)b | SA(r)b | DI | R | ||
KPG455B | SB(s)bc | SA(s)bc | 7 | K |
F = Flat Colour Profile. B = Bar. K = Presence of Knots. R = Ring. Sh = Shell. |
A reclassification of the galaxies in the (S+S) sample
was made using our CCD data. The original classifications
were made on the low resolution POSS. We revise the Hubble
classifications for at least one component in 44% of our
pairs (29 galaxies). An appreciable change in Hubble types
was found in 25 galaxies. The bulk of the
sample is comprised of (S+S) pairs. Very few galaxies could
be classified as irregular, and they may well be severely
distorted spirals. If we consider
as a
minimum value for morphological discordance in pairs, then
half of our pairs show morphological concordance between
pair members; 17 pairs (51%) show
and
16 pairs (49%)
.
This could explain, in
part, the strong correlation found between (B-V) colour
indices (Holmberg Effect) between members of this sample.
Elmegreen & Elmegreen (1982) developed a 12-division morphological system to classify spiral galaxies according to the regularity of their spiral arm structure. This spiral arm classification correlates with the presence of density waves as in grand design galaxies. Following that work, we succeeded in classifying 43 spirals. Some of the spirals in the global sample are nearly edge-on, strongly interacting or simply do not fit into the Elmegreen & Elmegreen classes. From 26 barred spirals, 18 are grand design and only 2 are flocculent. From 40 non-barred galaxies, 17 are grand design and 5 are flocculent. Grand design structure seems to be connected with binary galaxies, but strongly for barred than for non-barred galaxies. These results seem to be consistent with those of Elmegreen & Elmegreen (1982). We also have found knotty features in 24 galaxies and have detected rings or pseudo-ring features in 13 galaxies.
Interestingly, a fraction of the spirals have "open arms'' that could be interpreted in the framework of the simulations of Noguchi (1990 and references therein). The simulated galaxies have sizes similar to those in our sample. Noguchi's models follow both the stellar and gaseous component evolution in a disc galaxy during the encounter. Briefly speaking, in this scenario of moderate interactions, the bar develops quite soon and it is long-lasting, while the ring develops later and the gas follows the configuration of the ring. Four different phases may be seen: 1) open arms appear (integral sign) after perigalacticon, 2) a bar develops, the arms start to close and the gas start to follow the star configuration, 3) the arms are completely closed around the bar and form a ring; the gas is mainly concentrated in the center and ring, and 4) the ring starts to be disrupted by the dynamics and the overall appearance of the galaxy becomes nearly asymmetric.
As noted above, a fraction of the spirals in our sample (40%/20%) show (bar/ring) features which could be a transient phenomenon of the interaction in Noguchi's models. The bars are always redder while the rings and knots are always bluer compared with the galaxy outskirts. Most of the bridges and tails maintain the colour of the outskirts of the galaxies. The knotty structure along the arms and disks confirms the global nature of the star formation induced by the interactions. From 33 pairs, 20 can be classified according to the I/A class DI, 9 pairs as LI, and 4 pairs as NI. We have not detected any AT class, perhaps as a selection bias from our observing strategy. The sequence AT-LI-DI-NI has been interpreted as a sequence going from strongest to weak for tidal distortion or from most to least dynamically evolved. According to this, our (S+S) pairs are mainly involved in interactions of moderate level.
An interesting correlation has been found between the optical morphology and the global photometric properties in these pairs. From 26 barred galaxies, 15 show a flat behaviour (negligible gradient) in the azimuthally averaged colour profile while from 40 non-barred galaxies, 12 show flat colour profiles. This result may indicate that the bar acts unifying the stellar populations of the bulge and disk, in agreement with a secular evolutionary scenario, and consistent with the results in Gadotti & dos Anjos (2001) and Zaritsky et al. (1994) where barred spiral galaxies have flatter abundance gradients than unbarred spirals.
In order to analyze the photometrical signature of gravitational interactions in spiral galaxies, we present results of our BVRI surface photometry for a first set of 33 (S+S) pairs from the Karachentsev (1972) catalogue. We show that our derived parameters are generally in good agreement with those reported in RC3, aperture photometry catalogues and other individual photometric works. In addition, we present multiaperture photometry in order to facilitate further comparisons and contribute to the existing database of aperture photometry. The combination of 2D (B-I) colour maps and sharp/filtered B images appears to be a powerful technique both for morphological classification and for revealing fine structural details most likely related to encounters that are in various early and late stages. There is a tendency of barred galaxies to show grand design morphologies and flat colour profiles. In general our data suggest that our sample is undergoing moderate interactions which appear to be adequate to stimulate a nonaxisymmetric potential that generate a global response as evidenced by the presence of bars, rings, pseudo-rings and knotty structures along the arms and disks of the spiral galaxies in (S+S) pairs.
Acknowledgements
I.P. thanks the staff of the Observatorio Guillermo Haro for the help in the observations and also likes to thank E. Athanassoula for interesting discussions on spiral structure. These discussions were made possible via the ECOS/ANNUIES exchange project M99-U02, for which we are thankful. H.H.T. thanks J. Sulentic for his valuable comments. H.H.T. and I.P. thank the referee Dr. R. Rampazzo for his careful reading of this manuscript. His constructive criticism has helped us to clarify and focus our paper enormously.
Since the birth of galaxy photometry (Whitford 1936), the amount of photometric data has increased exponentially (Prugniel 1987). However, this data is inhomogeneous both in quality and format: photographic, photoelectric or more recently, CCD observations. The data are usually presented as centered aperture photometry through circular or elliptical apertures or as photometric profiles. In order to take into account the continuously growing amount of photometric data and at the same time, to make different photometric data reports somehow comparable, we present in Table A.1 our estimations of integrated magnitudes in three concentric circular apertures. Columns (2) and (3) give the logarithm of the aperture radius (in arcmin) for pair component (A) and (B). Columns (4)-(11) give their corresponding magnitudes in B, V, R and I bands, respectively. The small difference in aperture sizes suggest that the contribution of the sky to the errors in the magnitudes is relatively small. Typical uncertainties in the magnitudes are 0.15, 0.14, 0.15 and 0.14 in B, V, R and I bands respectively.
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Figure 5: KPG64 Mosaic. Top left: surface brightness and colour profiles. Top right: B-band image. Bottom left: B - I colour map. Bottom right: enhanced/filtered B-band image. North is to the top and East is to the left. |
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