517 research outputs found
A Deep HST H-Band Imaging Survey of Massive Gas-Rich Mergers. II. The QUEST PG QSOs
We report the results from a deep HST NICMOS H-band imaging survey of 28 z <
0.3 QSOs from the Palomar-Green (PG) sample. This program is part of QUEST
(Quasar / ULIRG Evolution STudy) and complements a similar set of data on 26
highly-nucleated ULIRGs presented in Paper I. Our analysis indicates that the
fraction of QSOs with elliptical hosts is higher among QSOs with undetected
far-infrared (FIR) emission, small infrared excess, and luminous hosts. The
hosts of FIR-faint QSOs show a tendency to have less pronounced merger-induced
morphological anomalies and larger QSO-to-host luminosity ratios on average
than the hosts of FIR-bright QSOs, consistent with late-merger evolution from
FIR-bright to FIR-faint QSOs. The spheroid sizes and total host luminosities of
the radio-quiet PG QSOs in our sample are statistically indistinguishable from
the ULIRG hosts presented in Paper I, while those of radio-loud PG QSOs are
systematically larger and more luminous. ULIRGs and PG QSOs with elliptical
hosts fall near, but not exactly on, the fundamental plane of inactive
spheroids. We confirm the systematic trend noted in Paper I for objects with
small (< 2 kpc) spheroids to be up to ~1 mag. brighter than inactive spheroids.
The host colors and wavelength dependence of their sizes support the idea that
these deviations are due at least in part to non-nuclear star formation.
However, the amplitudes of these deviations does not depend on host R-H colors.
Taken at face value (i.e., no correction for extinction or the presence of a
young stellar population), the H-band spheroid-host luminosities imply BH
masses ~5 -- 200 x 10^7 M_sun and sub-Eddington mass accretion rates for both
QSOs and ULIRGs. These results are compared with published BH mass estimates
derived from other methods. (abridged)Comment: Accepted for publication in the Astrophysical Journal, Vol. 701,
August 20 issue. Paper with high-resolution figures can be downloaded at
http://www.astro.umd.edu/~veilleux/pubs/nicmos2.pd
The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow
We present the best sensitivity and angular resolution maps of the molecular
disk and outflow of Mrk 231, as traced by CO observations obtained with
IRAM/PdBI, and we analyze archival Chandra and NuSTAR observations. We
constrain the physical properties of both the molecular disk and outflow, the
presence of a highly-ionized ultra-fast nuclear wind, and their connection. The
molecular outflow has a size of ~1 kpc, and extends in all directions around
the nucleus, being more prominent along the south-west to north-east direction,
suggesting a wide-angle biconical geometry. The maximum projected velocity of
the outflow is nearly constant out to ~1 kpc, thus implying that the density of
the outflowing material decreases from the nucleus outwards as . This
suggests that either a large part of the gas leaves the flow during its
expansion or that the bulk of the outflow has not yet reached out to ~1 kpc,
thus implying a limit on its age of ~1 Myr. We find and erg s.
Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow
(UFO) with velocity -20000 km s, , and momentum load .We find as predicted for outflows undergoing an energy
conserving expansion. This suggests that most of the UFO kinetic energy is
transferred to mechanical energy of the kpc-scale outflow, strongly supporting
that the energy released during accretion of matter onto super-massive black
holes is the ultimate driver of giant massive outflows. We estimate a momentum
boost . The ratios and agree
with the requirements of the most popular models of AGN feedback.Comment: 16 pages, 17 figures. Accepted for publication in A&
Keck High-Resolution Spectroscopy of Outflows in Infrared Luminous Galaxies
Several recent studies have determined that large quantities of neutral gas
are outflowing from the nuclei of almost all infrared-luminous galaxies. These
measurements show that winds in infrared-luminous galaxies play a significant
role in the evolution of galaxies and the intergalactic medium at redshifts z >
1, when infrared-luminous galaxies dominated the star formation rate of the
universe. These conclusions rely on moderate resolution spectra (FWHM > 65
km/s) of the NaI D absorption line and the assumption that there are no
unresolved, saturated velocity components. For the first time, we present high
resolution spectra (FWHM = 13 km/s) of massive, infrared-luminous galaxies. The
five galaxies in our sample are known to host outflows on the basis of previous
observations. With the present observations, all NaI D velocity components are
resolved with tau(NaI D1 5896 A) < 6. The column densities we measure are
consistent within the errors with those measured from moderate-resolution
observations. This confirms that the mass, momentum, and energy of outflowing
gas in infrared-luminous galaxies have been measured correctly by previous
studies.Comment: 1 figure; to be published in 2005 Sep 20 issue of ApJ
Extended Emission Line Gas in Radio Galaxies - PKS0349-27
PKS0349-27 is a classical FRII radio galaxy with an AGN host which has a
spectacular, spiral-like structure in its extended emission line gas (EELG). We
have measured the velocity field in this gas and find that it splits into 2
cloud groups separated by radial velocities which at some points approach 400
km/s Measurements of the diagnostic emission line ratios [OIII]5007/H-beta,
[SII]6716+6731/H-alpha, and [NII]6583/H-alpha in these clouds show no evidence
for the type of HII region emission associated with starburst activity in
either velocity system. The measured emission line ratios are similar to those
found in the nuclei of narrow-line radio galaxies, but the extended
ionization/excitation cannot be produced by continuum emission from the active
nucleus alone. We present arguments which suggest that the velocity
disturbances seen in the EELG are most likely the result of a galaxy-galaxy
collision or merger but cannot completely rule out the possibility that the gas
has been disrupted by the passage of a radio jet.Comment: 12 pages, 3 fig pages, to appear in the Astrophys.
Spitzer Quasar and ULIRG Evolution Study (QUEST). IV. Comparison of 1-Jy Ultraluminous Infrared Galaxies with Palomar-Green Quasars
We report the results from a comprehensive study of 74 ultraluminous infrared
galaxies (ULIRGs) and 34 Palomar-Green (PG) quasars within z ~ 0.3$ observed
with the Spitzer Infrared Spectrograph (IRS). The contribution of nuclear
activity to the bolometric luminosity in these systems is quantified using six
independent methods that span a range in wavelength and give consistent results
within ~ +/-10-15% on average. The average derived AGN contribution in ULIRGs
is ~35-40%, ranging from ~15-35% among "cool" (f_25/f_60 =< 0.2) optically
classified HII-like and LINER ULIRGs to ~50 and ~75% among warm Seyfert 2 and
Seyfert 1 ULIRGs, respectively. This number exceeds ~80% in PG QSOs. ULIRGs
fall in one of three distinct AGN classes: (1) objects with small extinctions
and large PAH equivalent widths are highly starburst-dominated; (2) systems
with large extinctions and modest PAH equivalent widths have larger AGN
contributions, but still tend to be starburst-dominated; and (3) ULIRGs with
both small extinctions and small PAH equivalent widths host AGN that are at
least as powerful as the starbursts. The AGN contributions in class 2 ULIRGs
are more uncertain than in the other objects, and we cannot formally rule out
the possibility that these objects represent a physically distinct type of
ULIRGs. A morphological trend is seen along the sequence (1)-(2)-(3), in
general agreement with the standard ULIRG - QSO evolution scenario and
suggestive of a broad peak in extinction during the intermediate stages of
merger evolution. However, the scatter in this sequence, implies that black
hole accretion, in addition to depending on the merger phase, also has a strong
chaotic/random component, as in local AGN. (abridged)Comment: 61 pages, 39 figures, 16 tables, accepted for publication in ApJS,
June 2009 issue. Unabbreviated version can be found at
http://www.astro.umd.edu/~veilleux/pubs/quest4.pd
NGC 839: Shocks in an M82-like Superwind
We present observations of NGC 839 made with the Wide Field Spectrograph
(WiFeS) on the ANU 2.3m telescope. Our data cover a region 25" x 60" at a
spatial resolution of ~1.5". The long axis of the field is aligned with the
superwind we have discovered in this starburst galaxy. The data cover the range
of 3700-7000 {\AA}, with a spectral resolution R~7000 in the red, and R~3000 in
the blue. We find that the stellar component of the galaxy is strongly
dominated by a fast rotating intermediate-age (~400 Myr) A-Type stellar
population, while the gas is concentrated in a bi-conical polar funnel. We have
generated flux distributions, emission line ratio diagnostics and velocity maps
in both emission and absorption components. We interpret these in the context
of a new grid of low-velocity shock models appropriate for galactic-scale
outflows. These models are remarkably well fit to the data, providing for the
first time model diagnostics for shocks in superwinds and strongly suggesting
that shock excitation is largely responsible for the extended LINER emission in
the outflowing gas in NGC 839. Our work may have important implications both
for extended LINER emission seen in other galaxies, as well as in the
interpretation of objects with "composite" spectra. Finally, we present a
scenario for the formation of E+A galaxies based upon our observations of NGC
839, and its relation to M82.Comment: 12 pages and 13 figures. Accepted for publication in Ap
The complexity of parsec-scaled dusty tori in AGN
Warm gas and dust surround the innermost regions of active galactic nuclei
(AGN). They provide the material for accretion onto the super-massive black
hole and they are held responsible for the orientation-dependent obscuration of
the central engine. The AGN-heated dust distributions turn out to be very
compact with sizes on scales of about a parsec in the mid-infrared. Only
infrared interferometry currently provides the necessary angular resolution to
directly study the physical properties of this dust. Size estimates for the
dust distributions derived from interferometric observations can be used to
construct a size--luminosity relation for the dust distributions. The large
scatter about this relation suggests significant differences between the dust
tori in the individual galaxies, even for nuclei of the same class of objects
and with similar luminosities. This questions the simple picture of the same
dusty doughnut in all AGN. The Circinus galaxy is the closest Seyfert 2 galaxy.
Because its mid-infrared emission is well resolved interferometrically, it is a
prime target for detailed studies of its nuclear dust distribution. An
extensive new interferometric data set was obtained for this galaxy. It shows
that the dust emission comes from a very dense, disk-like structure which is
surrounded by a geometrically thick, similarly warm dust distribution as well
as significant amounts of warm dust within the ionisation cone.Comment: 8 pages, 3 figures, to appear in the proceedings of the conference
"The central kiloparsec in Galactic Nuclei: Astronomy at High Angular
Resolution 2011", open access Journal of Physics: Conference Series (JPCS),
published by IOP Publishin
SDSS J1254+0846: A Binary Quasar Caught in the Act of Merging
We present the first luminous, spatially resolved binary quasar that clearly
inhabits an ongoing galaxy merger. SDSS J125455.09+084653.9 and SDSS
J125454.87+084652.1 (SDSS J1254+0846 hereafter) are two luminous z=0.44 radio
quiet quasars, with a radial velocity difference of just 215 km/s, separated on
the sky by 21 kpc in a disturbed host galaxy merger showing obvious tidal
tails. The pair was targeted as part of a complete sample of binary quasar
candidates with small transverse separations drawn from SDSS DR6 photometry. We
present follow-up optical imaging which shows broad, symmetrical tidal arm
features spanning some 75 kpc at the quasars' redshift. Numerical modeling
suggests that the system consists of two massive disk galaxies prograde to
their mutual orbit, caught during the first passage of an active merger. This
demonstrates rapid black hole growth during the early stages of a merger
between galaxies with pre-existing bulges. Neither of the two luminous nuclei
show significant instrinsic absorption by gas or dust in our optical or X-ray
observations, illustrating that not all merging quasars will be in an obscured,
ultraluminous phase. We find that the Eddington ratio for the fainter component
B is rather normal, while for the A component L/LEdd is quite (>3sigma) high
compared to quasars of similar luminosity and redshift, possibly evidence for
strong merger-triggered accretion. More such mergers should be identifiable at
higher redshifts using binary quasars as tracers.Comment: 15 pages, 5 figures, accepted to the Astrophysical Journal for the
February 2010 - 20 v710 issue. Latest version corrects author lis
High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel-PACS
We report the detection of far-infrared (FIR) CO rotational emission from
nearby active galactic nuclei (AGN) and starburst galaxies, as well as several
merging systems and Ultra-Luminous Infrared Galaxies (ULIRGs). Using
Herschel-PACS, we have detected transitions in the J = 14 - 20 range
( 130 - 185 m, 1612 - 2300 GHz) with upper limits
on (and in two cases, detections of) CO line fluxes up to J = 30. The
PACS CO data obtained here provide the first well-sampled FIR extragalactic CO
SLEDs for this range, and will be an essential reference for future high
redshift studies. We find a large range in the overall SLED shape, even amongst
galaxies of similar type, demonstrating the uncertainties in relying solely on
high-J CO diagnostics to characterize the excitation source of a galaxy.
Combining our data with low-J line intensities taken from the literature, we
present a CO ratio-ratio diagram and discuss its potential diagnostic value in
distinguishing excitation sources and physical properties of the molecular gas.
The position of a galaxy on such a diagram is less a signature of its
excitation mechanism, than an indicator of the presence (or absence) of warm,
dense molecular gas. We then quantitatively analyze the CO emission from a
subset of the detected sources with Large Velocity Gradient (LVG) radiative
transfer models to fit the CO SLEDs. Using both single-component and
two-component LVG models to fit the kinetic temperature, velocity gradient,
number density and column density of the gas, we derive the molecular gas mass
and the corresponding CO-to-H conversion factor, , for each
respective source. For the ULIRGs we find values in the canonical
range 0.4 - 5 M/(K kmspc), while for the other objects,
varies between 0.2 and 14.} Finally, we compare our best-fit LVG model
..Comment: 39 pages, 3 figures; Accepted to Ap
Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220
We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and
H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at
least 285 and \sim200 K, respectively, are detected in both sources, indicating
radiative pumping and location in the high radiation density environment of the
nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei
of both sources. The inferred OH+ column and abundance relative to H nuclei are
(0.5-1)x10^{16} cm-2 and \sim2x10^{-8}, respectively. Additionally, in Arp 220,
an extended low excitation component around the nuclear region is found to have
OH+/H2O+\sim5-10. H3O+ is detected in both sources with
N(H3O+)\sim(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable
lines indicate a high rotational temperature of ~500 K, indicative of formation
pumping and/or hot gas. Simple chemical models favor an ionization sequence
dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+
production is most likely dominated by X-ray/cosmic ray ionization. The full
set of observations and models leads us to propose that the molecular ions
arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in
which case the ionization rate per H nucleus (including secondary ionizations)
is zeta>10^{-13} s-1, a lower limit that is severalx10^2 times the highest rate
estimates for Galactic regions. In Arp 220, our lower limit for zeta is
compatible with estimates for the cosmic ray energy density inferred previously
from the supernova rate and synchrotron radio emission, and also with the
expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray
ionization due to an AGN is responsible for the molecular ion production.Comment: 24 pages, 13 figures. Accepted for publication in Astronomy &
Astrophysic
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