403 research outputs found
Outflows in Infrared-Luminous Starbursts at z < 0.5. II. Analysis and Discussion
We have performed an absorption-line survey of outflowing gas in 78
starburst-dominated, infrared-luminous galaxies. This is the largest study of
superwinds at z < 3. Superwinds are found in almost all infrared-luminous
galaxies, and changes in detection rate with SFR--winds are found twice as
often in ultraluminous infrared galaxies (ULIRGs) as in less-luminous
galaxies--reflect different wind geometries. The maximum velocities we measure
are 600 km/s, though most of the outflowing gas has lower velocities (100-200
km/s). (One galaxy has velocities exceeding 1000 km/s.) Velocities in LINERs
are higher than in HII galaxies, and outflowing ionized gas often has higher
velocities than the neutral gas. Wind properties (velocity, mass, momentum, and
energy) scale with galaxy properties (SFR, luminosity, and galaxy mass),
consistent with ram-pressure driving of the wind. Wind properties increase
strongly with increasing galactic mass, contrary to expectation. These
correlations flatten at high SFR (> 10-100 M_sun/yr), luminosities, and masses.
This saturation is due to a lack of gas remaining in the wind's path, a common
neutral gas terminal velocity, and/or a decrease in the efficiency of
thermalization of the supernovae energy. It means that mass entrainment
efficiency, rather than remaining constant, declines in galaxies with SFR > 10
M_sun/yr and M_K < -24. Half of our sample consists of ULIRGs, which host as
much as half of the star formation in the universe at z > 1. The powerful,
ubiquitous winds we observe in these galaxies imply that superwinds in massive
galaxies at redshifts above unity play an important role in the evolution of
galaxies and the intergalactic medium.Comment: 68 pages, 20 figures in AASTeX preprint style; to appear in September
issue of ApJS; Figure 17 replaced with correct versio
Half-Megasecond Chandra Spectral Imaging of the Hot Circumgalactic Nebula around Quasar Mrk 231
A deep 400-ksec ACIS-S observation of the nearest quasar known, Mrk 231, is
combined with archival 120-ksec data obtained with the same instrument and
setup to carry out the first ever spatially resolved spectral analysis of a hot
X-ray emitting circumgalactic nebula around a quasar. The 65 x 50 kpc X-ray
nebula shares no resemblance with the tidal debris seen at optical wavelengths.
One notable exception is the small tidal arc 3.5 kpc south of the nucleus where
excess soft X-ray continuum emission and Si XIII 1.8 keV line emission are
detected, consistent with star formation and its associated alpha-element
enhancement, respectively. An X-ray shadow is also detected at the location of
the 15-kpc northern tidal tail. The hard X-ray continuum emission within 6 kpc
of the center is consistent with being due entirely to the bright central AGN.
The soft X-ray spectrum of the outer (>6 kpc) portion of the nebula is best
described as the sum of two thermal components with T~3 and ~8 million K and
spatially uniform super-solar alpha element abundances, relative to iron. This
result implies enhanced star formation activity over ~10^8 yrs accompanied with
redistribution of the metals on large scale. The low-temperature thermal
component is not present within 6 kpc of the nucleus, suggesting extra heating
in this region from the circumnuclear starburst, the central quasar, or the
wide-angle quasar-driven outflow identified from optical IFU spectroscopy on a
scale of >3 kpc. Significant azimuthal variations in the soft X-ray intensity
are detected in the inner region where the outflow is present. The soft X-ray
emission is weaker in the western quadrant, coincident with a deficit of Halpha
and some of the largest columns of neutral gas outflowing from the nucleus.
Shocks created by the interaction of the wind with the ambient ISM may heat the
gas to high temperatures at this location. (abridged)Comment: 43 pages, 11 figures, accepted for publication in the Astrophysical
Journa
An Integral Field Study of Abundance Gradients in Nearby LIRGs
We present for the first time metallicity maps generated using data from the
Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies
(LIRGs) and discuss the abundance gradients and distribution of metals in these
systems. We have carried out optical integral field spectroscopy (IFS) of
several several LIRGs in various merger phases to investigate the merger
process. In a major merger of two spiral galaxies with preexisting disk
abundance gradients, the changing distribution of metals can be used as a
tracer of gas flows in the merging system as low metallicity gas is transported
from the outskirts of each galaxy to their nuclei. We employ this fact to probe
merger properties by using the emission lines in our IFS data to calculate the
gas-phase metallicity in each system. We create abundance maps and subsequently
derive a metallicity gradient from each map. We compare our measured gradients
to merger stage as well as several possible tracers of merger progress and
observed nuclear abundances. We discuss our work in the context of previous
abundance gradient observations and compare our results to new galaxy merger
models which trace metallicity gradient. Our results agree with the observed
flattening of metallicity gradients as a merger progresses. We compare our
results with new theoretical predictions that include chemical enrichment. Our
data show remarkable agreement with these simulations.Comment: Accepted for publication in ApJ. 26 pages, 18 figure
Outflows in Infrared-Luminous Starbursts at z < 0.5. I. Sample, NaI D Spectra, and Profile Fitting
We have conducted a spectroscopic survey of 78 starbursting infrared-luminous
galaxies at redshifts up to z = 0.5. We use moderate-resolution spectroscopy of
the NaI D interstellar absorption feature to directly probe the neutral phase
of outflowing gas in these galaxies. Over half of our sample are ultraluminous
infrared galaxies that are classified as starbursts; the rest have infrared
luminosities in the range log(L_IR/L_sun) = 10.2 - 12.0. The sample selection,
observations, and data reduction are described here. The absorption-line
spectra of each galaxy are presented. We also discuss the theory behind
absorption-line fitting in the case of a partially-covered, blended absorption
doublet observed at moderate-to-high resolution, a topic neglected in the
literature. A detailed analysis of these data is presented in a companion
paper.Comment: 59 pages, 18 figures in AASTeX preprint style; to appear in September
issue of ApJ
Quasar Feedback in the Ultraluminous Infrared Galaxy F11119+3257: Connecting the Accretion Disk Wind with the Large-Scale Molecular Outflow
In Tombesi et al. (2015), we reported the first direct evidence for a quasar
accretion disk wind driving a massive molecular outflow. The target was
F11119+3257, an ultraluminous infrared galaxy (ULIRG) with unambiguous type-1
quasar optical broad emission lines. The energetics of the accretion disk wind
and molecular outflow were found to be consistent with the predictions of
quasar feedback models where the molecular outflow is driven by a hot
energy-conserving bubble inflated by the inner quasar accretion disk wind.
However, this conclusion was uncertain because the energetics were estimated
from the optically thick OH 119 um transition profile observed with Herschel.
Here, we independently confirm the presence of the molecular outflow in
F11119+3257, based on the detection of broad wings in the CO(1-0) profile
derived from ALMA observations. The broad CO(1-0) line emission appears to be
spatially extended on a scale of at least ~7 kpc from the center. Mass outflow
rate, momentum flux, and mechanical power of (80-200) R_7^{-1} M_sun/yr,
(1.5-3.0) R_7^{-1} L_AGN/c, and (0.15-0.40)% R_7^{-1} L_AGN are inferred from
these data, assuming a CO-to-H_2 conversion factor appropriate for a ULIRG (R_7
is the radius of the outflow normalized to 7 kpc and L_AGN is the AGN
luminosity). These rates are time-averaged over a flow time scale of 7x10^6
yrs. They are similar to the OH-based rates time-averaged over a flow time
scale of 4x10^5 yrs, but about a factor 4 smaller than the local
("instantaneous"; <10^5 yrs) OH-based estimates cited in Tombesi et al. The
implications of these new results are discussed in the context of time-variable
quasar-mode feedback and galaxy evolution. The need for an energy-conserving
bubble to explain the molecular outflow is also re-examined.Comment: 15 pages, 6 figures, 4 tables, accepted for publication in Ap
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
Exploring the Dust Content of Galactic Winds with Herschel. I. NGC 4631
We present a detailed analysis of deep far-infrared observations of the
nearby edge-on star-forming galaxy NGC 4631 obtained with the Herschel Space
Observatory. Our PACS images at 70 and 160 um show a rich complex of filaments
and chimney-like features that extends up to a projected distance of 6 kpc
above the plane of the galaxy. The PACS features often match extraplanar
Halpha, radio-continuum, and soft X-ray features observed in this galaxy,
pointing to a tight disk-halo connection regulated by star formation. On the
other hand, the morphology of the colder dust component detected on larger
scale in the SPIRE 250, 350, and 500 um data matches the extraplanar H~I
streams previously reported in NGC 4631 and suggests a tidal origin. The PACS
70/160 ratios are elevated in the central ~3.0 kpc region above the nucleus of
this galaxy (the "superbubble"). A pixel-by-pixel analysis shows that dust in
this region has a higher temperature and/or an emissivity with a steeper
spectral index (beta > 2) than the dust in the disk, possibly the result of the
harsher environment in the superbubble. Star formation in the disk seems
energetically insufficient to lift the material out of the disk, unless it was
more active in the past or the dust-to-gas ratio in the superbubble region is
higher than the Galactic value. Some of the dust in the halo may also have been
tidally stripped from nearby companions or lifted from the disk by galaxy
interactions.Comment: Accepted for publication in The Astrophysical Journa
Spitzer Quasar and ULIRG evolution study (QUEST): I. The origin of the far infrared continuum of QSOs
This paper addresses the origin of the far-infrared (FIR) continuum of QSOs,
based on the Quasar and ULIRG Evolution Study (QUEST) of nearby QSOs and ULIRGs
using observations with the Spitzer Space Telescope. For 27 Palomar-Green QSOs
at z <~ 0.3, we derive luminosities of diagnostic lines ([NeII]12.8um,
[NeV]14.3um, [OIV]25.9um) and emission features (PAH7.7um emission which is
related to star formation), as well as continuum luminosities over a range of
mid- to far-infrared wavelengths between 6 and 60um. We detect star-formation
related PAH emission in 11/26 QSOs and fine-structure line emission in all of
them, often in multiple lines. The detection of PAHs in the average spectrum of
sources which lack individual PAH detections provides further evidence for the
widespread presence of PAHs in QSOs. Similar PAH/FIR and [NeII]/FIR ratios are
found in QSOs and in starburst-dominated ULIRGs and lower luminosity
starbursts. We conclude that the typical QSO in our sample has at least 30% but
likely most of the far-infrared luminosity (~ 10^(10...12)Lsun) arising from
star formation, with a tendency for larger star formation contribution at the
largest FIR luminosities. In the QSO sample, we find correlations between most
of the quantities studied including combinations of AGN tracers and starburst
tracers. The common scaling of AGN and starburst luminosities (and fluxes) is
evidence for a starburst-AGN connection in luminous AGN. Strong correlations of
far-infrared continuum and starburst related quantities (PAH, low excitation
[NeII]) offer additional support for the starburst origin of far-infrared
emission.Comment: 39 pages, 8 figures, accepted for publication in Ap
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