Issue |
A&A
Volume 519, September 2010
|
|
---|---|---|
Article Number | A5 | |
Number of page(s) | 8 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/200913953 | |
Published online | 06 September 2010 |
The redshift and broad-band spectral
energy distribution of
NRAO 150![[*]](/icons/foot_motif.png)
J. A. Acosta-Pulido1,2 - I. Agudo3,4 - R. Barrena1,2 - C. Ramos Almeida1,2,5 - A. Manchado1,2 - P. Rodríguez-Gil1,6
1 - Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea, s/n,
38200, La Laguna, Tenerife, Spain
2 - Departamento de Astrofísica, Universidad de La Laguna, 38205 La
Laguna, Tenerife, Spain
3 - Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, 18080
Granada, Spain
4 - Institute for Astrophysical Research, Boston University, 725
Commonwealth Avenue, Boston, MA 02215, USA
5 - Department of Physics & Astronomy, University of Shefield,
UK
6 - Isaac Newton Group of Telescopes, La Palma, Spain
Received 23 December 2009 / Accepted 9 March 2010
Abstract
Context. NRAO 150 is one of the
brightest radio and mm AGN sources in the northern sky, and is an
interesting source to study extreme relativistic jet phenomena.
However, its cosmological distance has not yet been calibrated, because
of its optical faintness due to strong Galactic extinction.
Aims. We measure the redshift of
NRAO 150, to enable us to perform quantitative
studies of the source.
Methods. We conducted spectroscopic and photometric
observations of the source in both the near-IR and the optical.
Results. All these observations were successful in
detecting the source. The near-IR spectroscopic observations exhibit
strong H
and H
emission lines from which the cosmological redshift of
NRAO 150 (
)
is determined for the first time. We classify the source as a
flat-spectrum radio-loud quasar, for which we estimate a high
supermassive black-hole mass
.
After extinction correction, the new near-IR and optical data show a
high-luminosity continuum-emission excess in the optical (peaking in
the rest frame at
2000 Å)
that we attribute to thermal emission from the accretion disk for which
we estimate a high accretion rate of
30% the Eddington limit.
Conclusions. Comparison of the source properties and
its broad-band spectral-energy distribution with those of Fermi
blazars allows us to predict that NRAO 150 is among
the most powerful of blazars, and hence a high luminosity - although
not yet detected - -ray
emitter.
Key words: galaxies: active - galaxies: jets - quasars: emission lines - quasars: individual: NRAO 150 - quasars: general
1 Introduction
First catalogued by Pauliny-Toth
et al. (1966), NRAO 150 is
nowadays one of the
strongest radio and mm AGN sources in
the northern sky (e.g., Agudo et al. 2010; Teräsranta
et al. 2005).
The source has been monitored at cm and mm wavelengths for decades
(e.g., Teräsranta
et al. 2004; Reuter et al. 1997; Aller
et al. 1985, and references therein), and displayed
flux densities in the range [2, 16] Jy at 2 cm and
[1.5, 9.5] Jy at
3 mm
, its absolute maxima
having occurred at the beginning of year 2009.
At radio wavelengths, NRAO 150 displays on
VLBI scales, a compact core
plus a one-sided jet extending up to mas with a jet
structural
position angle (PA) of
(e.g., Fey & Charlot 2000).
The first set of ultra-high-resolution mm-VLBI images of
NRAO 150
(Agudo et al. 2007)
allowed them to detect a large misalignment (
)
between the cm-wave and the
mm-wave jet, which in addition to the one sidedness of the jet, is a
clear sign
of jet orientation close to the line of sight.
There has also been evidence of rapid ``jet wobbling'' at
11
yr in the
plane of the sky, which is the most rapid for an AGN found so far.
The observations by Agudo
et al. (2007) together with the cosmological
redshift
measurement presented in this paper and non-contemporaneous X-ray data
have allowed them to report the first quantitative estimates of the
basic physical properties of the inner jet in
NRAO 150, i.e., Doppler
factor
,
the bulk Lotentz factor
,
the angle
subtended between the jet and the line of sight
,
and
the magnetic field intensity of the flow
G.
This high B estimate seems to be compatible with
the highly non-balistic
superluminal motion of the inner jet in the source detected by the
mm-VLBI
images (
times the speed of light), which have also
demonstrated that NRAO 150 is a prime target for
studying the origin of the jet wobbling
phenomenon (Agudo 2009).
In the optical, NRAO 150 was first detected
in December 1981 by Landau
et al. (1983).
However, no optical classification or distance determination has been
reported
so far, perhaps because of the difficulties in observing the source at
visible wavelengths,
where NRAO 150 is strongly affected by Galactic
extinction
(Galactic latitude
).
This problem is partially overcome in the near-IR range, where
spectroscopic
observations from strong-lined objects can be performed from Earth.
Independent of the Galactic absorption along the line of sight to the
source, the
near-IR range is an adequate spectral range for detecting the strong H
line
from AGN at cosmological redshifts between 1.2 and 3.6 (e.g., Babbedge et al. 2004).
![]() |
Figure 1: Final reduced spectrum of NRAO 150. The position of the most prominent features are marked. Deep atmospheric absorption bands are indicated by vertical bands. Top panel: spectra corresponding to the bands Z+J observed at two epochs. The thicker red color line corresponds to observations performed in March 2005, and the thinner blue color line corresponds to those of January 2007. Middle and bottom panels: spectra corresponding to the bands H and K, respectively. |
Open with DEXTER |
Here, we present the results of our spectroscopic near-IR observations, which were successful in detecting, for the first time, emission lines from NRAO 150. In Sect. 2, these observations and their data reduction procedures are outlined and applied to a set of optical and near-IR photometric observations performed in the 2005-2007 time span. The cosmological redshift determination, the classification, and the first estimate of the mass of the supermassive compact object in NRAO 150 and both its accretion rate and broad-band spectral energy distribution, are presented and discussed in Sects. 3 and 4, whereas a summary of our main results and conclusions are provided in Sect. 5.
2 Observations and data reduction
2.1 Near infrared spectroscopy
We obtained near-IR spectroscopy of NRAO 150 using the Long-slit Intermediate Resolution Infrared Spectrograph (LIRIS, built at the Instituto de Astrofísica de Canarias Acosta-Pulido et al. 2003; Manchado et al. 2004) on the 4.2 m William Herschel Telescope (WHT) in two epochs (2005 March and 2007 January).
The spectra were obtained using grisms LR_ZJ (bands Z+J)
and LR_HK (bands H+K).
For the observations in 2005, the slit width was selected to be ,
providing resolutions of 700 and 600 in the Z+J
and H+K bands,
respectively. For those in 2007, the slit width was 1'' to match the
seeing, providing a resolution of 500 in the Z+J bands.
The slit orientation (
)
was chosen to include in the slit
aperture both NRAO 150 and the object 2MASS J03592889+5057547.
The observations were performed following an ABBA telescope nodding
pattern, each AB cycle being repeated 3 times. The exposure time for a
single frame was 600 s, giving a total of 3600 s for
both spectral ranges. The data were reduced following standard recipes
for near-IR spectroscopy, using the dedicated software lirisdr,
developed within the IRAF
enviroment by the LIRIS team. The basic reduction steps comprise sky
subtraction, flat-fielding, wavelength calibration, and finally, the
combination of
individual spectra by the common shift-and-add
technique. For a more detailed description of the reduction process, we
refer to Ramos
Almeida et al. (2009,2006).
The flux calibration and telluric absorption correction are usually
determined
from observations of nearby stars of spectral types A0V or G2V, which
are obtained inmediately before or after the science observations. In
the first epoch, the selected correction star was found to be a
multiple
stellar system whose 2MASS near-IR colors indicate a spectral type that
differs from A0.
We determined a spectral response function using the spectrum of the
star 2MASS J03592889+5057547, which was observed simultaneously with
NRAO 150.
The stellar spectral shape was corrected by a black body of temperature
corresponding to an M5 spectral type.
A posteriori, we derived the telluric correction from the normalized
spectrum of star 2MASS J03592889+5057547. During the second epoch, an
A0V star was successfully observed.
A modified version of the Xtellcor routine was used (Vacca et al. 2003) to
obtain the calibrated flux
and telluric-corrected NRAO 150 spectrum. Relative
light losses due to atmospheric
differential refraction are very small, always below a few percent,
despite the slit not being oriented at the parallactic angle.
The flux calibrated spectra are presented in Fig. 1.
2.2 Near infrared photometry
We obtained images in the J and
filters using LIRIS at the same epochs as the near-IR spectroscopy. In
both cases, the images were obtained following a 5 point dithering
pattern. Individual frames of 20 and 10 s were taken in the J
and
filters,
respectively, providing the total exposure times reported in
Table 2.
The images were reduced using the task ldedither
included in the dedicated software package lirisdr,
developed in IRAF by the LIRIS team. The main data reduction steps are
sky subtraction, flat-field correction, and finally a combination of
the images after proper alignment.
The photometric calibration was determined by comparing with
the 2-MASS catalogue (Cutri
et al. 2003). The zero points of our J
and
photometry were determined using about 20 stars with
known 2-MASS magnitudes (brighter than
)
included in the LIRIS field. The typical dispersion between
instrumental and 2-MASS magnitudes is
0.08.
2.3 Optical photometry
In addition to the near-IR observations, we also obtained images in the optical using several telescopes at different epochs. The first observations were performed using the CCD camera mounted on the IAC-80 at the Teide Observatory during the nights of 2005 Nov. 2 and 11. We used filters V, R, and I (see Table 1). Our target was detected in all bands (see Fig. 2 for examples of I and V images). Given the faintness of the source, a larger diameter telescope, the 2.5 m Liverpool robotic telescope (Steele et al. 2004) was used to perform the remaining observations. Filters Johnson V and Sloan r' and i' were used, although most data were obtained only in r' (see Table 1).
Table 1: Observing log.
Table 2: NRAO 150 - Optical near-IR photometry.
All data were reduced in IRAF following the standard
procedures, i.e., bias subtraction, flat-fielding, and image
combination. The photometric calibration was based on images of Landolt
fields
obtained in photometric conditions. The photometry was obtained using
the SExtractor program (Bertin
& Arnouts 1996) and the AUTOMAG parameter. The
resulting photometric measurements are listed in Table 2. We estimated
that the detection of faint objects in our images is complete to V=23.1
(24.0) mag, r'=21.7 (23.0) mag,
and i'=20.4 (21.5) mag for
(3) within the observed fields.
Based on our photometric calibration, we propose seven reference stars for r' and i' filters to be used in future monitoring. These stars are marked in Fig. 2 and their corresponding magnitudes are listed in Table 3.
![]() |
Figure 2: Identification charts of NRAO 150 in I and V filters. The circle and square symbols mark NRAO 150 and the star 2MASS J03592889+505754, used as reference for spectroscopy. Dashed square represent the plotted area in V band. North and east are toward the top and left of the frame, respectively. Numbers note the calibration stars proposed for this field. |
Open with DEXTER |
3 Results
3.1 Near IR spectrum
A very prominent feature is observed in the spectrum of
NRAO 150 in the
H band at 1.65 m (see
Fig. 1).
A less intense, but notable, feature is also seen in the J band
at
1.23
m. These are
identified with the H
and H
lines, respectively, redshifted by
providing
the first redshift determination of NRAO 150.
The corresponding luminosity distance of the source is
Mpc,
for a
H0=71 km s-1 Mpc-1,
,
and
cosmology
.
We measured the center, width, and flux of the narrow and
broad components of H
and H
by fitting two Gaussian components plus a slope as the continuum (see
Table 4).
We started by fitting H
since this part of the spectrum has a higher
signal-to-noise ratio and is not contaminated by other feature, such as
FeII
emission. The H
profile is accurately fitted by a narrow component of
Å
(1458 km s-1 rest-frame) and a
broad component of
Å
(5745 km s-1 rest-frame).
The broad component is blueshifted with respect to the narrow component
by 62 Å (532 km s-1).
In the case of H
the S/N ratio is much lower and we were unable to allow the line widths
to
vary in the fitting. Instead they were constrained by the best fit
solution for H
.
Other broad features of lower S/N are observed around
4300 Å (rest frame), corresponding to the Balmer limit,
and at 4450-4700, 4924, 5018 and 5150-5350 Å, associated with
blends of FeII emission (see Fig. 1). To remove
and confirm the importance of FeII emission, we subtracted the
empirical FeII emission template
of Boroson & Green (1992),
scaled to the intensity of the observed features (see
Fig. 3).
This template was generated from a spectrum of
PG 0050+124 (IZw 1), which is distinctive because of
the strength of its FeII emission
and the narrowness of its H recombination lines (Oke & Lauer 1979). The
template (kindly provided by Dr. P. Marziani) was prepared by removing
the lines not associated with Fe II transitions. From
Fig. 3,
it can be seen that after the FeII template subtraction the residual
spectra exhibits uniquely the broad H
feature, and
a shallow bump at 4300 Å corresponding to the Balmer limit.
Given the radio loud AGN properties of NRAO 150,
it is expected to observe intense narrow forbidden emission lines, such
as [OIII]
5007 Å,
[NII]
6548 Å,
6584 Å,
and [SII]
6716,
6731 Å.
However, none of these features are detected at a significant level
over the continuum. The implications of weak or absent typical NLR
features are discussed in Sect. 4.2.
Table 3: Photometry of reference stars near NRAO 150.
![]() |
Figure 3:
Top panel: the two NRAO 150 spectra
(histogram style line) taken at different
epochs are represented together with a scaled version of the IZw1
template (green continuous thin line).
Bottom panel: the spectra after subtraction
of the template. It can be seen
that the residual spectra consist basically on a broad H |
Open with DEXTER |
3.2 Optical and near IR variability
Our optical and near-IR photometric measurements span a range of almost
2 years (see Table 2),
which is typically a sufficiently long time range to detect intrinsic
variability in radio-loud AGN
(e.g., Teräsranta
et al. 2004,2005).
NRAO 150 exhibits a nearly monotonic radio flux
increase by a factor 4
from 1991 to 2005 (Teräsranta
et al. 2004,2005). However, we cannot
make any firm claim about optical variability based on measurements in
the r' band, the band with by far the
longer and more frequently sample coverage in terms of time.
The maximum magnitude variations observed are
0.2 mag, which are not larger than
3 times the typical measurement uncertainty. We note that part
of the data were taken using different combinations of filters,
cameras, and
telescopes, which does not enhance their homogeneity. The faintness of
the source in the optical
range also prevents us from obtaining more accurate photometric
measurements.
As in the optical range, our near-IR photometric measurements
(performed in 2005 March and 2006 December) do not exhibit significant
variability of amplitude above 0.3 mag (
0.25 or 30%). A similar result is
obtained when our near-IR measurements are compared with those of the
2-MASS survey in 1999 (see Table 2). In this case,
maximum variability amplitudes of
mag
and
mag
are found, which contrasts with the factor of 2 flux density
increase reported by Teräsranta
et al. (2005) at radio wavelengths for the same time
range.
This suggests that the process responsible for the radio emission is
not
connected to that responsible for the optical and near IR emission.
Table 4:
Flux units are .
Luminosity units are
.
4 Discussion
4.1 Black hole mass and its accretion efficiency
We use the empirical relationships provided by Vestergaard & Peterson (2006)
to estimate the central black hole mass in NRAO 150.
The black hole (BH) mass can be estimated from the luminosity and width
of the broad component of the H
line using expresion 6 in Vestergaard
& Peterson (2006). Given the low S/N ratio
of the H
line detected in our spectral measurements, the use of the line
luminosity is preferable to the value of the continuum at
5100 Å (used in Eq. (5) of Vestergaard & Peterson 2006).
The measured broad component luminosity is
,
which increases to
after applying the
Galactic extinction correction derived in this work (see
Appendix A).
Combining these values with those for the line width (see
Table 4),
the resulting black hole mass is
,
which converts to
after
extinction correction. Using the estimate of the black hole mass, we
can also determine the
corresponding Eddington luminosity [
],
which results in a value of
To compute the accretion rate, this value must be compared with the
bolometric
luminosity of the accretion disk, which results in
,
and
after
extinction correction. The disk luminosity was computed by integrating
the measured fluxes within the optical-UV range in the rest frame, this
value is multiplied by
to obtain the luminosity. Here it is assumed that the radio-mm and the
X-ray emission
are related to the relativistic jet. This is justified given the
variability in the optical-UV spectral ranges, which is uncoupled
with that in the radio-mm as reported in Sect. 3.2.
Thus the Eddington luminosity ratio is
.
These values can be compared to those previously reported in
the literature for similar objects.
The black hole mass of NRAO 150 is above the highest
masses found in the literature for low redshift AGNs (Vestergaard & Peterson 2006),
although the estimated value for M 87, is
(Graham 2007), comparable to
that of NRAO 150. In contrast, the black hole mass
of NRAO 150 is well within the range of typical
masses of luminous high redshift AGNs (Shemmer
et al. 2004). Several works
(e.g., McLure
& Dunlop 2004; Shen et al. 2008) have
tried to measure the dependence of the mean BH mass on
redshift. They reach a common
result: the mean BH mass increases with redshift, although this
dependence is dominated by the Malmquist bias (Vestergaard et al. 2008).
Labita et al. (2009)
claimed that the maximum BH mass evolves with z as
,
whereas the
maximum Eddington ratio (0.45) is essentially constant with z.
However, Labita et al. (2009)
suggest that these results are
unaffected by the Malmquist bias. Our estimate for the BH mass in
NRAO 150 is slightly above the maximum value, and
the Eddington ratio is also close to the maximum value, which indicates
that NRAO 150 contains a very massive and efficiently
accreting BH.
4.2 FeII emission and weakness of the NLR emission features
As reported above, the spectrum of NRAO 150 presents
both prominent H
recombination lines and intense FeII emission, in contrast to the very
weak or absent lines characteristic of the
NLR, such as [OIII] (see Fig. 3). Netzer et al. (2004)
found that about one third of very high luminosity AGNs do not exhibit
strong [OIII] lines. In addition, an anticorrelation between
EW(FeII)/EW(H)
and EW([OIII]) (Netzer
et al. 2004; Boroson & Green 1992; Yuan & Wills
2003) is reported.
In our NRAO 150 spectra, the estimated EWs of H
,
FeII, and [OIII] are around 55, 60, and 6, although the uncertainties
are large given the difficulty in deblending the spectral features.
These values are consistent with the afore mentioned results. Using
these values, we checked that NRAO 150 is placed in
Fig. 9 of Netzer et al.
(2004) on the locus of high luminosity and high-redshift QSO
sample. The location of NRAO 150 in Fig. 3 of Netzer et al. (2004) is
in-between that of PG QSOs (Bennert
et al. 2002) and z>2 QSOs
in terms of its H
luminosity.
Netzer et al. (2004)
suggest that for highly luminous QSOs the NLR becomes extremely large
(even larger than the size of the
biggest galaxies) as expected from the ``natural''
dependence,
which makes the NLR to disappear and become dynamically unbound. The
equivalent size of the NLR in NRAO 150, as predicted
from the H
luminosity (
),
is about 20 kpc (Fig. 3 in Netzer
et al. 2004), which is well above the sizes commonly
reported for typical NLR, hence explaining the weakness of the NLR
emission features in our spectra.
![]() |
Figure 4: Spectral energy distribution (SED) of NRAO 150 from the radio to the X-ray spectral range after correction for Galactic extinction. Filled circles represent Galactic extinction estimated in this work (see Appendix A), and empty circles represent the extinction estimated from IRAS far-IR emission maps (Schlegel et al. 1998). Empty triangles indicate the extinction-uncorrected optical and near-IR measurements, and we note the dramatic change of the SED after extinction correction is applied. The measurements presented here were obtained almost contemporaneously during year 2005 (see text), except for the ROSAT X-ray data (bow tie), which were acquired between August 1990 and February 1991. |
Open with DEXTER |
4.3 The spectral energy distribution
Figure 4
shows the spectral energy distribution (SED) of
NRAO 150. In addition to the photometric data
presented here, we searched for data covering the widest possible
wavelength range, from radio to X-rays. At radio bands, measurements of
the lowest frequency,
obtained at 4, 8.4, 22, and 43 GHz with the VLA on March 2005,
were taken from
the National Radio Astronomy Observatory
data archive. The subsequent three measurements were observed
at 86, 142, and 229 GHz as part of the
general IRAM 30-m Telescope AGN monitoring program (Reuter et al. 1997, and
references
therein) on March 2005 (August 2005 for the higher frequency one).
The optical-UV rest-frame observations corresponds to the near-IR and
the optical observations presented here, and were acquired on March
2005 and November 2005, respectively.
In this spectral region, empty triangles indicate the
extinction-uncorrected
optical and near-IR measurements. Empty circles correspond to these
measurements
corrected for the Galactic extinction estimated from IRAS far-IR
emission maps
(Schlegel et al. 1998),
whereas filled circles indicate the same measurements
corrected for the more accurate Galactic extinction estimated here (see
Appendix A).
The X-ray data, acquired by ROSAT from August 1990 and February 1991,
were corrected by Galactic extinction as reported in Agudo et al. (2007). For
the plot in Fig. 4,
a photon index
was assumed
based on the synchrotron spectrum measured from the IRAM 30 m
observations
presented here at 86 and 142 GHz (spectral index
).
The SED of NRAO 150 exhibits two prominent bumps: one
peaking around 1 mm and another
at 2000 Å. The low frequency SED bump resembles those typical
of high power flat-spectrum radio-loud sources (e.g., Ghisellini et al. 2009a,b).
This first bump is attributed to strong Doppler-boosted synchrotron
relativistic-jet-emission.
The X-ray domain of the SED is also typical of inverse Compton emission
from
the jet, whereas the high luminosity optical-UV bump
(
erg/s at
Hz)
is not so commonly reported for this kind of source.
A prominent peak at optical-UV (rest frame) wavelengths is typical of
Seyfert galaxies and is understood to be produced by thermal emission
from the AGN accretion disk.
However, there is an increasing number of high-power radio-loud blazars
for which this
emission feature is being reported (e.g., Ghisellini et al. 2009a;
D'Ammando
et al. 2009; Ghisellini & Tavecchio 2009;
Abdo
et al. 2009; Raiteri et al. 2007,b).
Nearly half of the radio loud blazars in the sample considered by
Ghisellini et al.
(2009a) were reported to exhibit a similar optical-UV large
excess. There is a consensus toward considering this emission to come
from thermal emission
from the accretion disk (e.g., Ghisellini et al. 2009a;
D'Ammando
et al. 2009; Ghisellini & Tavecchio 2009;
Abdo
et al. 2009; Raiteri et al. 2007,b),
which is not overwhelmed by the synchrotron bump from the jet when this
bump peaks at
Hz.
We also agree that this is a likely explanation for
NRAO 150 because of the
reasons outlined by Ghisellini
et al. (2009b).
This also explains the above-mentioned lack of variability in the
observed optical and near-IR bands of NRAO 150,
whereas the radio and mm
spectral ranges showed a factor 5 long term variability. This can be
easily explained if this observed optical and near-IR (rest frame
optical-UV)
emission is produced in the accretion disk and not in the relativistic
jets
where the extreme variability originates.
4.4 Source classification
From the VLBI point of view, NRAO 150 shows a
one-sided powerful
relativistic-superluminal jet typical of blazars, which indicates that
the axis must be aligned close to the line of sight.
Its radio spectrum is typically flat, which classifies the source as a
flat spectrum radio quasar (FSRQ). The optical rest-frame spectrum
contains
intense and broad (5000 km s-1)
H
and H
emission,
so the source is a type 1 AGN, consistent with the disk axis
being aligned close to the line of sight according to the standard AGN
unification scenario (Urry &
Padovani 1995). The optical and
radio properties are both consistent given the orientation of the radio
jet and the
accretion disk.
That the forbidden [OIII] lines are weak
points to a very luminous central engine, which is also consistent with
the high Eddington rate determined from the optical/UV luminosity
relative to the BH mass. The high accretion rate is consistent with the
high radio loudness of NRAO 150. The BH mass is also
among the highest in value derived for quasars (Ghisellini et al. 2009b;
Vestergaard
& Peterson 2006; Vestergaard et al. 2008,
and references therein).
5 Summary and conclusions
We have determined, for the first time, the cosmological distance of
NRAO 150, one of the brightest radio to mm AGN
sources in the northern sky, by means of its spectroscopic redshift (z=1.517
or Mpc).
Given the low Galactic latitude of the source, its optical spectral
lines have remained hidden from us for decades.
The new near-IR spectra presented here have detected very intense H
emission and weaker H
and FeII blended lines.
The measured line width of H
implies that NRAO 150 is a broad-line AGN. Its disk
axis must be oriented close to the line of sight, indicating that it is
a powerful one-sided superluminal radio-mm jet.
Based also on its radio to mm spectral and variability properties
(including those observed with VLBI), NRAO 150 can
be classified as a FSRQ blazar.
In agreement with previous observations of high redshift and highly
luminous quasars, the optical rest-frame spectrum of the source exhibit
weak or absent spectral features typical of the NLR, such as [OIII]
Å.
This implies that the highest luminosity accretion disks (and probably
the most massive BH) probably experience the unbounding of their NLR by
accretion disk radiation.
Using empirical relationships between H
line width and luminosity we estimate that the central engine in
NRAO 150 cotains a massive black hole of mass
.
The radio to X-rays SED of the source exhibit two prominent bumps: one
peaking at millimetre wavelengths - typical of synchrotron radiation
from high power blazar jets - and another in the near-UV (
2000 Å)
that is attributable to thermal emission from the accretion disk.
The good spectral coverage of the disk emission allows us to measure
reliably the bolometric luminosity of the disk, which turns out to be
accreted at
30%
of the Eddington rate. This, the high BH mass of the source, its
prominent BLR line luminosity, and its highly luminous synchrotron
spectrum implies that NRAO 150 is one of the most
powerful FSRQ blazars.
These sources are also the most luminous hard X-ray and
-ray
inverse-Compton blazar emitters (Ghisellini et al. 2009a;
Ghisellini
& Tavecchio 2009,b), and are routinely monitored by
high energy space observatories such as Fermi. We
predict that NRAO 150 is one of these sources.
However, it has not yet been detected in
-rays.
The low Galactic latitude of the source presents a challenge for
-rays
observatories to detect it.
If this were possible in the future, modeling of the whole broad-band
spectrum SED would allow us to investigate further the intrinsic
physical parameters of this powerful blazar.
Financial support by the grant AYA2004-03136 from Plan Nacional de Astronomía y Astrofísica is acknowledged. I.A. acknowledges support by an I3P contract with the Spanish ``Consejo Superior de Investigaciones Científicas'', and by the Spanish ``Ministerio de Ciencia e Innovación'' and the European Fund for Regional Development through grant AYA2007-67627-C03-03. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Some of the data published in this article were acquired with the IAC80 telescope operated by the Instituto de Astrofísica de Canarias in the Observatorio del Teide. We gratefully acknowledge H. Ungerechts for providing total flux density mm measurements from the general IRAM 30-meter Telescope AGN Monitoring Program. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).
Appendix A: Galactic extinction correction
We have already mentioned that the low Galactic latitude of NRAO 150 and its associated high Galactic extinction has defied optical identification and studies of this radio-source. To compute the intrinsic properties of NRAO 150, we have to correct for the Galactic extinction. As a first approach, we have taken the extinction from SIMBAD database, which is estimated from far infrared emission maps build by combining IRAS and COBE/DIRBE data (Schlegel et al. 1998). The quoted value is E(B-V)=1.474, which implies that the extinction is between AV=4.5 and AK=0.54.
To obtain another estimate of the Galactic extinction in the
direction of NRAO 150, we compiled a color-magnitude
diagram (Fig. A.1)
using the near infrared colors (J and K
from 2MASS database Cutri
et al. 2003) of neighbouring stars.
The color-magnitude (
,
J) diagram stellar distribution was compared with
the theoretical isochrones for 2MASS filters retrieved from Girardi et al. (2002).
We attempted to discern part of the Main Sequence in the
color-magnitude diagrams and recognized two possible ones (see
Fig. A.1),
one being, more crowded, and showing an excess
and a second sequence, less populated, with
.
We identified the first population to be in front of the Galactic disk
and the other to be behind the disk and presenting a higher galactic
extinction.
When we assumed the solar metalicity z=0.019,
we found that the closest possible fits to both stellar populations
corresponded to isochrones with Gyr
(see Fig. A.1).
For these fits, we computed
for a stellar population with a distance module of 10.2, and
and a distance module of 9.5 for the less extincted and closer
population. We were only interested in the largest value of E(J-K),
which implies a
value
(E(B-V)=1.69 E(J-K)).
This value is in reasonable agreement with the estimate provided by the
SIMBAD database.
![]() |
Figure A.1:
Color-magnitude diagram of a field of |
Open with DEXTER |
References
- Abdo, A. A., Ackermann, M., Ajello, M., et al. 2009, ApJ, 699, 976 [NASA ADS] [CrossRef] [Google Scholar]
- Acosta Pulido, J. A., Ballesteros, E., Barreto, M., et al. 2003, INGN, 7, 15A [NASA ADS] [Google Scholar]
- Agudo, I. 2009, in Approaching Micro-Arcsecond Resolution with VSOP-2: Astrophysics and Technologies, ed. Y. Hagiwara, E. Fomalont, M. Tsuboi, & Y. Murata, ASP Conf. Ser., 402, 330 [Google Scholar]
- Agudo, I., Bach, U., Krichbaum, T. P., et al. 2007, A&A, 476, L17 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Agudo, I., Thum, C., Wiesemeyer, H., & Krichbaum, T. P. 2010, ApJS, 189, 1 [NASA ADS] [CrossRef] [Google Scholar]
- Aller, H. D., Aller, M. F., Latimer, G. E., & Hodge, P. E. 1985, ApJS, 59, 513 [NASA ADS] [CrossRef] [Google Scholar]
- Babbedge, T. S.-R., Rowan-Robinson, M., Gonzalez-Solares, E., et al. 2004, MNRAS, 353, 654 [NASA ADS] [CrossRef] [Google Scholar]
- Bennert, N., Falcke, H., Schulz, H., Wilson, A. S., & Wills, B. J. 2002, ApJ, 574, L105 [NASA ADS] [CrossRef] [Google Scholar]
- Bertin, E., & Arnouts, S. 1996, A&AS, 117, 393 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Boroson, T. A., & Green, R. F. 1992, ApJS, 80, 109 [NASA ADS] [CrossRef] [Google Scholar]
- Cutri, R. M., et al. 2003, VizieR On-line Data Catalog: II/246, Originally published in: University of Massachusetts and Infrared Processing and Analysis Center (IPAC/California Institute of Technology) [Google Scholar]
- D'Ammando, F., Pucella, G., Raiteri, C. M., et al. 2009, A&A, 508, 181 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Fey, A. L., & Charlot, P. 2000, ApJS, 128, 17 [NASA ADS] [CrossRef] [Google Scholar]
- Ghisellini, G., & Tavecchio, F. 2009, MNRAS, 397, 985 [NASA ADS] [CrossRef] [Google Scholar]
- Ghisellini, G., Tavecchio, F., & Ghirlanda, G. 2009a, MNRAS, 399, 2041 [NASA ADS] [CrossRef] [Google Scholar]
- Ghisellini, G., Foschini, L., Volonteri, M., et al. 2009b, MNRAS, 399, L24 [NASA ADS] [CrossRef] [Google Scholar]
- Girardi 2002, A&A, 391, 195 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Graham, A. W. 2007, MNRAS, 379, 711 [NASA ADS] [CrossRef] [Google Scholar]
- Labita, M., Decarli, R., Treves, A., & Falomo, R. 2009, MNRAS, 396, 1537 [NASA ADS] [CrossRef] [Google Scholar]
- Landau, R., Jones, T. W., Epstein, E. E., et al. 1983, ApJ, 268, 68 [NASA ADS] [CrossRef] [Google Scholar]
- Manchado, A., Barreto, M., Acosta-Pulido, J. A., et al. 2004, in Proc. SPIE, 5492, 1094 [Google Scholar]
- McLure, R. J., & Dunlop, J. S. 2004, MNRAS, 352, 1390 [NASA ADS] [CrossRef] [Google Scholar]
- Netzer, H., Shemmer, O., Maiolino, R., et al. 2004, ApJ, 614, 558 [NASA ADS] [CrossRef] [Google Scholar]
- Oke, J. B., & Lauer, T. R. 1979, ApJ, 230, 360 [NASA ADS] [CrossRef] [Google Scholar]
- Pauliny-Toth, I. I. K., Wade, C. M., & Heeschen, D. S. 1966, ApJ, 13, 65 [NASA ADS] [CrossRef] [Google Scholar]
- Raiteri, C. M., Villata, M., Larionov, V. M., et al. 2007, A&A, 473, 819 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Ramos Almeida, C., Pérez García, A. M., Acosta-Pulido, J. A., et al. 2006, ApJ, 645, 148 [NASA ADS] [CrossRef] [Google Scholar]
- Ramos Almeida, C., Pérez García, A. M., & Acosta-Pulido, J. A. 2009, ApJ, 694, 1379 [NASA ADS] [CrossRef] [Google Scholar]
- Reuter, H.-P., Kramer, C., Sievers, A., et al. 1997, A&AS, 122, 271 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525 [NASA ADS] [CrossRef] [Google Scholar]
- Shemmer, O., Netzer, H., Maiolino, R., et al. 2004, ApJ, 614, 547 [NASA ADS] [CrossRef] [Google Scholar]
- Shen, Y., Greene, J. E., Strauss, M. A., Richards, G. T., & Schneider, D. P. 2008, ApJ, 680, 169 [NASA ADS] [CrossRef] [Google Scholar]
- Steele, I. A., Smith, R. J., Rees, P. C., et al. 2004, in Ground-based Telescopes, ed. J. M. Oschmann, Jr., Proc. SPIE, 5489, 679 [Google Scholar]
- Teräsranta, H., Achren, J., Hanski, M., et al. 2004, A&A, 427, 769 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Teräsranta, H., Wiren, S., Koivisto, P., Saarinen., V., & Hovatta, T. 2005, A&A, 440, 409 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
- Vacca, W. D., Cushing, M. C., & Rayner, J. T. 2003, PASP, 115, 389 [NASA ADS] [CrossRef] [Google Scholar]
- Vestergaard, M., & Peterson, B. M. 2006, ApJ, 641, 689 [NASA ADS] [CrossRef] [Google Scholar]
- Vestergaard, M., Fan X., Tremonti, C. A., Osmer, P. S., & Richards, G. T. 2008 ApJ, 674, L1 [Google Scholar]
- Yuan, M. J., & Wills, B. J. 2003, ApJ, 593, L11 [NASA ADS] [CrossRef] [Google Scholar]
- Urry, C. M., & Padovani, P. 1995, PASP, 107, 803 [NASA ADS] [CrossRef] [Google Scholar]
Footnotes
- ...
NRAO 150
- Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
- ... 2 cm
- http://www.astro.lsa.umich.edu/obs/radiotel
- ...
3 mm
- H. Ungerechts, private communication.
- ... IRAF
- IRAF (Image Reduction and Analysis Facility) is distributed by the National Optical Astronomy Observatories, which are operated by AURA, Inc., under cooperative agreement with the National Science Foundation.
- ... cosmology
- The cosmology calculator available in the Web (http://www.astro.ucla.edu/ wright/CosmoCalc.html) was used.
- ... Observatory
- The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
All Tables
Table 1: Observing log.
Table 2: NRAO 150 - Optical near-IR photometry.
Table 3: Photometry of reference stars near NRAO 150.
Table 4:
Flux units are .
Luminosity units are
.
All Figures
![]() |
Figure 1: Final reduced spectrum of NRAO 150. The position of the most prominent features are marked. Deep atmospheric absorption bands are indicated by vertical bands. Top panel: spectra corresponding to the bands Z+J observed at two epochs. The thicker red color line corresponds to observations performed in March 2005, and the thinner blue color line corresponds to those of January 2007. Middle and bottom panels: spectra corresponding to the bands H and K, respectively. |
Open with DEXTER | |
In the text |
![]() |
Figure 2: Identification charts of NRAO 150 in I and V filters. The circle and square symbols mark NRAO 150 and the star 2MASS J03592889+505754, used as reference for spectroscopy. Dashed square represent the plotted area in V band. North and east are toward the top and left of the frame, respectively. Numbers note the calibration stars proposed for this field. |
Open with DEXTER | |
In the text |
![]() |
Figure 3:
Top panel: the two NRAO 150 spectra
(histogram style line) taken at different
epochs are represented together with a scaled version of the IZw1
template (green continuous thin line).
Bottom panel: the spectra after subtraction
of the template. It can be seen
that the residual spectra consist basically on a broad H |
Open with DEXTER | |
In the text |
![]() |
Figure 4: Spectral energy distribution (SED) of NRAO 150 from the radio to the X-ray spectral range after correction for Galactic extinction. Filled circles represent Galactic extinction estimated in this work (see Appendix A), and empty circles represent the extinction estimated from IRAS far-IR emission maps (Schlegel et al. 1998). Empty triangles indicate the extinction-uncorrected optical and near-IR measurements, and we note the dramatic change of the SED after extinction correction is applied. The measurements presented here were obtained almost contemporaneously during year 2005 (see text), except for the ROSAT X-ray data (bow tie), which were acquired between August 1990 and February 1991. |
Open with DEXTER | |
In the text |
![]() |
Figure A.1:
Color-magnitude diagram of a field of |
Open with DEXTER | |
In the text |
Copyright ESO 2010
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.