24 research outputs found
Torus skin outflow in a near-Eddington quasar revealed by spectropolarimetry
Even when the direct view toward the active nucleus is obscured, nuclear
emission propagating along other directions can scatter off surrounding
material, become polarized and reach the observer. Spectropolarimetry can thus
be an important tool in investigating the circumnuclear geometry and kinematics
of quasars on scales that cannot yet be probed via direct observations. Here we
discuss an intriguing class of quasars where the polarization position angle
swings by large amounts (90 deg) within an emission line. We investigate a
kinematic model in which the scattering dust or electrons are in an
axisymmetric outflow. We propagate Stokes parameters in a variety of geometries
of emitter, scatterer and observer. We use these models to predict polarization
fraction, line profiles and polarization position angles and compare them to
observations. We demonstrate that the swinging polarization angle can be a
result of the geometry of the outflow and the orientation of the observer.
Polarization properties of a near-Eddington extremely red quasar SDSS J1652 can
be successfully explained by a model in which the quasar is surrounded by a
geometrically thick disk, whose `skin' is outflowing at 1000 km/s and acts as
the scatterer on scales of a few tens of pc. The line of sight to the observer
in this source is within or close to the skin of the torus, in agreement with
multi-wavelength data. Spectropolarimetric data and models presented here
strongly support the thick-disk geometry of circumnuclear material suggested by
recent numerical simulations of high-rate accretion flows onto black holes.Comment: 17 pages, accepted to MNRA
Sensitive Radio Survey of Obscured Quasar Candidates
We study the radio properties of moderately obscured quasars over a range of
redshifts to understand the role of radio activity in accretion using the
Jansky Very Large Array (JVLA) at 6.0GHz and 1.4GHz. Our z~2.5 sample consists
of optically-selected obscured quasar candidates, all of which are radio-quiet,
with typical radio luminosities of [1.4 GHz] < erg
s. Only a single source is individually detected in our deep (rms~10
Jy) exposures. This population would not be identified by radio-based
selection methods used for distinguishing dusty star-forming galaxies and
obscured active nuclei. In our pilot A-array study of z~0.5 radio-quiet
quasars, we spatially resolve four of five objects on scales ~ 5 kpc and find
they have steep spectral indices. Therefore, radio emission in these sources
could be due to jet-driven or radiatively driven bubbles interacting with
interstellar material on the scale of the host galaxy. Finally, we also study
the population of ~ 200 faint (~40 Jy - 40 mJy) radio sources observed
over ~ 120 arcmin of our data. 60% of these detections are matched in the
SDSS and/or WISE and are, in roughly equal shares, active nuclei at a broad
range of redshifts, passive galaxies with no other signs of nuclear activity
and IR-bright but optically faint sources. Spectroscopically or photometrically
confirmed star-forming galaxies constitute only a small minority of the
matches. Such sensitive radio surveys allow us to address important questions
of AGN evolution and evaluate the AGN contribution to the radio-quiet sky.Comment: 18 pages, submitted to MNRA
Winds as the origin of radio emission in radio-quiet extremely red quasars
Most active galactic nuclei (AGNs) are radio-quiet, and the origin of their
radio emission is not well-understood. One hypothesis is that this radio
emission is a by-product of quasar-driven winds. In this paper, we present the
radio properties of 108 extremely red quasars (ERQs) at . ERQs are among
the most luminous quasars ( erg/s) in the Universe,
with signatures of extreme ( km/s) outflows in their
[OIII]5007 \AA\ emission, making them the best subjects to seek the
connection between radio and outflow activity. All ERQs but one are unresolved
in the radio on kpc scales, and the median radio luminosity of ERQs
is erg/s, in the radio-quiet regime, but
one to two orders of magnitude higher than that of other quasar samples. The
radio spectra are steep, with a mean spectral index . In addition, ERQs neatly follow the extrapolation of the low-redshift
correlation between radio luminosity and the velocity dispersion of
[OIII]-emitting ionized gas. Uncollimated winds, with a power of one per cent
of the bolometric luminosity, can account for all these observations. Such
winds would interact with and shock the gas around the quasar and in the host
galaxy, resulting in acceleration of relativistic particles and the consequent
synchrotron emission observed in the radio. Our observations support the
picture in which ERQs are signposts of extremely powerful episodes of quasar
feedback, and quasar-driven winds as a contributor of the radio emission in the
intermediate regime of radio luminosity erg/s.Comment: accepted by MNRA
Host galaxies of high-redshift extremely red and obscured quasars
We present Hubble Space Telescope 1.4-1.6 micron images of the hosts of ten
extremely red quasars (ERQs) and six type 2 quasar candidates at z=2-3. ERQs,
whose bolometric luminosities range between 10^47 and 10^48 erg/sec, show
spectroscopic signs of powerful ionized winds, whereas type 2 quasar candidates
are less luminous and show only mild outflows. After performing careful
subtraction of the quasar light, we clearly detect almost all host galaxies.
The median rest-frame B-band luminosity of the ERQ hosts in our sample is
10^11.2 L_Sun, or 4 L* at this redshift. Two of the ten hosts of ERQs are in
ongoing mergers. The hosts of the type 2 quasar candidates are 0.6 dex less
luminous, with 2/6 in likely ongoing mergers. Intriguingly, despite some signs
of interaction and presence of low-mass companions, our objects do not show
nearly as much major merger activity as do high-redshift radio-loud galaxies
and quasars. In the absence of an overt connection to major ongoing gas-rich
merger activity, our observations are consistent with a model in which the
near-Eddington accretion and strong feedback of ERQs are associated with
relatively late stages of mergers resulting in early-type remnants. These
results are in some tension with theoretical expectations of galaxy formation
models, in which rapid black hole growth occurs within a short time of a major
merger. Type 2 quasar candidates are less luminous, so they may instead be
powered by internal galactic processes.Comment: Accepted to MNRAS; 23 pages, including 9 figures and 2 table
High-redshift Extremely Red Quasars in X-Rays
Quasars may have played a key role in limiting the stellar mass of massive galaxies. Identifying those quasars in the process of removing star formation fuel from their hosts is an exciting ongoing challenge in extragalactic astronomy. In this paper, we present X-ray observations of 11 extremely red quasars (ERQs) with L bol ~ 1047 erg s−1 at z = 1.5–3.2 with evidence for high-velocity (v 1000 km s−1) [O iii] λ5007 outflows. X-rays allow us to directly probe circumnuclear obscuration and to measure the instantaneous accretion luminosity. We detect 10 out of 11 ERQs available in targeted and archival data. Using a combination of X-ray spectral fitting and hardness ratios, we find that all of the ERQs show signs of absorption in the X-rays with inferred column densities of N H ≈ 1023 cm−2, including four Compton-thick candidates (N H 1024 cm−2). We stack the X-ray emission of the seven weakly detected sources, measuring an average column density of N H ~ 8 × 1023 cm−2. The absorption-corrected (intrinsic) 2–10 keV X-ray luminosity of the stack is 2.7 × 1045 erg s−1, consistent with X-ray luminosities of type 1 quasars of the same infrared luminosity. Thus, we find that ERQs are a highly obscured, borderline Compton-thick population, and based on optical and infrared data we suggest that these objects are partially hidden by their own equatorial outflows. However, unlike some quasars with known outflows, ERQs do not appear to be intrinsically underluminous in X-rays for their bolometric luminosity. Our observations indicate that low X-rays are not necessary to enable some types of radiatively driven winds
The Hunt for Red Quasars : Luminous Obscured Black Hole Growth Unveiled in the Stripe 82 X-Ray Survey
We present results of a ground-based near-infrared campaign with Palomar TripleSpec, Keck NIRSPEC, and Gemini GNIRS to target two samples of reddened active galactic nucleus (AGN) candidates from the 31 deg(2) Stripe 82 X-ray survey. One sample, which is similar to 89% complete to K 4, Vega). The fainter sample (K > 17, Vega) represents a pilot program to follow-up four sources from a parent sample of 34 that are not detected in the single-epoch SDSS catalog and have WISE quasar colors. All 12 sources are broad-line AGNs (at least one permitted emission line has an FWHM exceeding 1300 km s(-1)) and span a redshift range 0.59 0.5), and a greater percentage have high X-ray luminosities (L-X,L- full > 10(44) erg s(-1)). Such outflows and high luminosities may be consistent with the paradigm that reddened broad-line AGNs represent a transitory phase in AGN evolution as described by the major merger model for black hole growth. Results from our pilot program demonstrate proof of concept that our selection technique is successful in discovering reddened quasars at z > 1 missed by optical surveys.Peer reviewe
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
Spectropolarimetry of high-redshift obscured and red quasars
Spectropolarimetry is a powerful technique that has provided critical support
for the geometric unification model of local active galactic nuclei. In this
paper, we present optical (rest-frame UV) Keck spectropolarimetry of five
luminous obscured (Type 2) and extremely red quasars (ERQs) at z~2.5. Three
objects reach polarization fractions of >10% in the continuum. We propose a
model in which dust scattering is the dominant scattering and polarization
mechanism in our targets, though electron scattering cannot be completely
excluded. Emission lines are polarized at a lower level than is the continuum.
This suggests that the emission-line region exists on similar spatial scales as
the scattering region. In three objects we detect an intriguing 90 degree swing
in the polarization position angle as a function of line-of-sight velocity in
the emission lines of Ly-alpha, CIV and NV. We interpret this phenomenon in the
framework of a geometric model with an equatorial dusty scattering region in
which the material is outflowing at several thousand km/sec. Emission lines may
also be scattered by dust or resonantly. This model explains several salient
features of observations by scattering on scales of a few tens of pc. Our
observations provide a tantalizing view of the inner region geometry and
kinematics of high-redshift obscured and extremely red quasars. Our data and
modeling lend strong support for toroidal obscuration and powerful outflows on
the scales of the UV emission-line region, in addition to the larger scale
outflows inferred previously from the optical emission-line kinematics.Comment: 26 pages, MNRAS, in pres