445 research outputs found
Infrared Diagnostics for the Extended 12 micron Sample of Seyferts
We present an analysis of Spitzer IRS spectroscopy of 83 active galaxies from
the extended 12 micron sample. We find rank correlations between several
tracers of star formation which suggest that (1) the PAH feature is a reliable
tracer of star formation, (2) there is a significant contribution to the
heating of the cool dust by stars, (3) the H emission is also primarily
excited by star formation. The 55-90 vs. 20-30 spectral index plot is also a
diagnostic of the relative contribution of Starburst to AGN. We see there is a
large change in spectral index across the sample. Thus, the contribution to the
IR spectrum from the AGN and starburst components can be comparable in
magnitude but the relative contribution also varies widely across the sample.
We find rank correlations between several AGN tracers. We search for
correlations between AGN and Starburst tracers and we conclude that the AGN and
Starburst tracers are not correlated. This is consistent with our conclusion
that the relative strength of the AGN and Starburst components varies widely
across the sample. Thus, there is no simple link between AGN fueling and Black
Hole Growth and star formation in these galaxies. The distribution of Sil 10
micron and 18 micron strengths is consistent with the clumpy torus models of
Sirocky et al. We find a rank correlation between the [NeV] 14 micron line and
the 6.7 micron continuum which may be due to an extended component of hot dust.
The Sy 2s with a Hidden Broad Line Region (HBLR) have a higher ratio of AGN to
Starburst contribution to the SED than Sy 2s without an HBLR. This may
contribute to the detection of the HBLR in polarized light. The Sy 2s with an
HBLR are more similar to the Sy 1s than they are to the Sy 2s without an HBLR
A Search for Molecular Gas in GHz Peaked Spectrum Radio Sources
We present searches for molecular gas (CO, OH, CS, and Ammonia) in six GHz
Peaked Spectrum (GPS) radio sources. We do not detect gas in any source and
place upper limits on the mass of molecular gas which are generally in the
range 1E9 to a few times 1E10 solar masses. These limits are consistent with
the following interpretations: (1) GPS sources do not require very dense gas in
their hosts, and (2) The GPS sources are unlikely to be confined by dense gas
and will evolve to become larger radio sources
Evidence for Ordered Magnetic Fields in the Quasar Environment
At a distance of 20 pc from the purported supermassive black hole powering
quasars, temperatures and densities are inferred from optical observations to
be ~10**4 K and ~10**4 cm**-3. Here we present Very Long Baseline
Interferometry radio observations revealing organized magnetic fields on the
parsec scale in the hot plasma surrounding the quasar OQ172 (1442+101). These
magnetic fields rotate the plane of polarization of the radio emission coming
from the core and inner jet of the quasar. The derived rotation measure (RM) is
40,000 rad m**-2 in the rest frame of the quasar. Only 10 mas (a projected
distance of 68 pc) from the nucleus the jet absolute values of RM fall to less
than 100 rad m**-2.Comment: in press at ApJ Letters, 12 page LaTeX document includes 4 postscript
figure
HI absorption in 3C 49 and 3C 268.3. Probing the environment of Compact Steep Spectrum and GHz Peaked Spectrum sources
We present and discuss European VLBI Network UHF band spectral line
observations, made to localise the redshifted 21cm HI absorption known to occur
in the subgalactic sized compact steep spectrum galaxies 3C 49 and 3C 268.3. We
have detected HI absorption towards the western radio lobe of 3C 49 and the
northern lobe of 3C 268.3. However, we cannot rule out the presence of similar
amounts of HI towards the opposite and much fainter lobes. The radio lobes with
detected HI absorption (1) are brighter and closer to the core than the
opposite lobes; (2) are depolarized; and (3) are associated with optical
emission line gas. The association between the HI absorption and the emission
line gas, supports the hypothesis that the HI absorption is produced in the
atomic cores of the emission line clouds. Our results are consistent with a
picture in which compact steep spectrum sources interact with clouds of dense
gas as they propagate through their host galaxy. We suggest that the
asymmetries in the radio and optical emission can be due to interaction of a
two sided radio source with an asymmetric distribution of dense clouds in their
environment.Comment: 7 pages, 6 figures. Accepted in A&
Large-Scale Outflows in Edge-on Seyfert Galaxies. I. Optical Emission- Line Imaging and Optical Spectroscopy
We have launched a search for large-scale (\gapprox1 kpc) minor-axis
outflows in edge-on Seyfert galaxies in order to assess their frequency of
occurrence and study their properties. Here we present optical continuum and
\han2 line images and/or minor-axis long-slit spectra of 22 edge-on Seyfert
galaxies. Six of these galaxies show at least one of the following: (i)
bi-symmetric H halos extending along the minor axis, (ii) bright
emission-line complexes at distances \gapprox4 kpc (in projection) out of the
disk, and (iii) double-peaked emission-line profiles from the gas along the
minor-axis, suggesting that a wind-blown bubble is present. Our results
indicate that \gapprox of Seyferts have good evidence for
minor-axis galactic outflows. Kinetic luminosities of the galactic outflows in
our sample Seyferts are 1010 erg~s, assuming all
of the observed minor-axis emission is produced by the outflow. These values
are, in general, 0.1 as large as those for well-studied cases of
superwinds in starburst galaxies (Heckman, Armus \& Miley 1990). However,
far-infrared luminosities of our sample Seyferts are also 0.1 as large.
Both starburst-driven superwinds and wide-angled outflows from the active
galactic nucleus are possible explanations for the observed large-scale
outflows.Comment: 34 pages (text and tables) AASTEX, figures available from
[email protected], ApJ Supp., June 199
Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments
CMB experiments aiming at a precise measurement of the CMB polarization, such
as the Planck satellite, need a strong polarized absolute calibrator on the sky
to accurately set the detectors polarization angle and the cross-polarization
leakage. As the most intense polarized source in the microwave sky at angular
scales of few arcminutes, the Crab nebula will be used for this purpose. Our
goal was to measure the Crab nebula polarization characteristics at 90 GHz with
unprecedented precision. The observations were carried out with the IRAM 30m
telescope employing the correlation polarimeter XPOL and using two orthogonally
polarized receivers. We processed the Stokes I, Q, and U maps from our
observations in order to compute the polarization angle and linear polarization
fraction. The first is almost constant in the region of maximum emission in
polarization with a mean value of alpha_Sky=152.1+/-0.3 deg in equatorial
coordinates, and the second is found to reach a maximum of Pi=30% for the most
polarized pixels. We find that a CMB experiment having a 5 arcmin circular beam
will see a mean polarization angle of alpha_Sky=149.9+/-0.2 deg and a mean
polarization fraction of Pi=8.8+/-0.2%.Comment: Accepted for publication in A&A, 9 pages, 4 figure
The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source?
Context. Radio-loud AGNs with powerful relativistic jets are thought to be
associated with rapidly spinning black holes (BHs). BH spin-up may result from
a number of processes, including accretion of matter onto the BH itself, and
catastrophic events such as BH-BH mergers. Aims. We study the intriguing
properties of the powerful (L_bol ~ 10^47 erg s^-1) radio-loud quasar 3C 186.
This object shows peculiar features both in the images and in the spectra.
Methods. We utilize near-IR Hubble Space Telescope (HST) images to study the
properties of the host galaxy, and HST UV and Sloan Digital Sky Survey optical
spectra to study the kinematics of the source. Chandra X-ray data are also used
to better constrain the physical interpretation. Results. HST imaging shows
that the active nucleus is offset by 1.3 +- 0.1 arcsec (i.e. ~11 kpc) with
respect to the center of the host galaxy. Spectroscopic data show that the
broad emission lines are offset by -2140 +-390 km/s with respect to the narrow
lines. Velocity shifts are often seen in QSO spectra, in particular in
high-ionization broad emission lines. The host galaxy of the quasar displays a
distorted morphology with possible tidal features that are typical of the late
stages of a galaxy merger. Conclusions. A number of scenarios can be envisaged
to account for the observed features. While the presence of a peculiar outflow
cannot be completely ruled out, all of the observed features are consistent
with those expected if the QSO is associated with a gravitational wave (GW)
recoiling BH. Future detailed studies of this object will allow us to confirm
this type of scenario and will enable a better understanding of both the
physics of BH-BH mergers and the phenomena associated with the emission of GW
from astrophysical sources.Comment: 16 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. New appendix adde
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