75 research outputs found
The Complex Structure of the Multi-Phase Galactic Wind in a Starburst Merger
Neutral outflows have been detected in many ultraluminous infrared galaxies
(ULIRGs) via the Na I D absorption-line doublet.
For the first time, we have mapped and analyzed the 2-D kinematics of a cool
neutral outflow in a ULIRG, F10565+2448, using the integral field unit (IFU) on
Gemini North to observe the Na I D feature. At the same time we have mapped the
ionized outflow with the [NII] and H emission lines. We find a systemic
rotation curve that is consistent with the rotation of the molecular disk
determined from previous CO observations. The absorption lines show evidence of
a nuclear outflow with a radial extent of at least 3 kpc, consistent with
previous observations. The strength of the Na I D lines have a strong,
spatially resolved correlation with reddening, suggesting that dust is present
in the outflow. Surprisingly, the outflow velocities of the neutral gas show a
strong asymmetry in the form of a major-axis gradient that is opposite in sign
to disk rotation. This is inconsistent with entrained material rotating along
with the galaxy or with a tilted minor-axis outflow. We hypothesize that this
unusual behavior is due to an asymmetry in the distribution of the ambient gas.
We also see evidence of asymmetric ionized outflow in the emission-line
velocity map, which appear to be decoupled from the neutral outflow. Our
results strengthen the hypothesis that ULIRG outflows differ in morphology from
those in more quiescent disk galaxies.Comment: Accepted to Ap
The Infrared Database of Extragalactic Observables from Spitzer I: the redshift catalog
This is the first of a series of papers on the Infrared Database of
Extragalactic Observables from Spitzer (IDEOS). In this work we describe the
identification of optical counterparts of the infrared sources detected in
Spitzer Infrared Spectrograph (IRS) observations, and the acquisition and
validation of redshifts. The IDEOS sample includes all the spectra from the
Cornell Atlas of Spitzer/IRS Sources (CASSIS) of galaxies beyond the Local
Group. Optical counterparts were identified from correlation of the extraction
coordinates with the NASA Extragalactic Database (NED). To confirm the optical
association and validate NED redshifts, we measure redshifts with unprecedented
accuracy on the IRS spectra ({\sigma}(dz/(1+z))=0.0011) by using an improved
version of the maximum combined pseudo-likelihood method (MCPL). We perform a
multi-stage verification of redshifts that considers alternate NED redshifts,
the MCPL redshift, and visual inspection of the IRS spectrum. The statistics is
as follows: the IDEOS sample contains 3361 galaxies at redshift 0<z<6.42 (mean:
0.48, median: 0.14). We confirm the default NED redshift for 2429 sources and
identify 124 with incorrect NED redshifts. We obtain IRS-based redshifts for
568 IDEOS sources without optical spectroscopic redshifts, including 228 with
no previous redshift measurements. We provide the entire IDEOS redshift catalog
in machine-readable formats. The catalog condenses our compilation and
verification effort, and includes our final evaluation on the most likely
redshift for each source, its origin, and reliability estimates.Comment: 11 pages, 6 figures, 1 table. Accepted for publication in MNRAS. Full
redshift table in machine-readable format available at
http://ideos.astro.cornell.edu/redshifts.htm
Elliptical Galaxy in the Making: The Dual Active Galactic Nuclei and Metal-enriched Halo of Mrk 273
A systematic analysis of the X-ray emission from the nearby ultraluminous
infrared galaxy Mrk 273 was carried out by combining new 200 ksec Chandra data
with archived 44 ksec data. The active galactic nucleus (AGN) associated with
the Southwest nucleus is confirmed by the new data, and a secondary hard X-ray
(4-8 keV) point source is detected, coincident with the Northeast nucleus at a
projected distance of 0.75 kpc from the Southwest nucleus. The hard X-ray
spectrum of the Northeast nucleus is consistent with a heavily absorbed AGN,
making Mrk 273 another example of a dual AGN in a nearby galaxy merger.
Significant 1-3 keV emission is found along the ionization cones and outflowing
gas detected in a previous study. The data also map the giant X-ray nebula
south of the host galaxy with unprecedented detail. This nebula extends on a
scale of 40 kpc 40 kpc, and is not closely related to the
well-known tidal tail seen in the optical. The X-ray emission of the nebula is
best described by a single-temperature gas model, with a temperature of
7 million K and a super-solar /Fe ratio. Further analysis suggests that
the southern nebula has most likely been heated and enriched by multiple
galactic outflows generated by the AGN and/or circumnuclear starburst in the
past, on a time scale of 0.1 Gyr, similar to the merger event itself.Comment: 25 pages, 22 figures, 4 tables, accepted for publication in the
Astrophysical Journa
Metallicity gradients in local field star-forming galaxies: Insights on inflows, outflows, and the coevolution of gas, stars and metals
We present metallicity gradients in 49 local field star-forming galaxies. We
derive gas-phase oxygen abundances using two widely adopted metallicity
calibrations based on the [OIII]/Hbeta, [NII]/Halpha and [NII]/[OII] line
ratios. The two derived metallicity gradients are usually in good agreement
within +/-0.14 dex/R25 (R25 is the B-band iso-photoal radius), but the
metallicity gradients can differ significantly when the ionisation parameters
change systematically with radius. We investigate the metallicity gradients as
a function of stellar mass (8<log(M*/Msun)<11) and absolute B-band luminosity
(-16 > MB > -22). When the metallicity gradients are expressed in dex/kpc, we
show that galaxies with lower mass and luminosity, on average, have steeper
metallicity gradients. When the metallicity gradients are expressed in dex/R25,
we find no correlation between the metallicity gradients, and stellar mass and
luminosity. We provide a local benchmark metallicity gradient of field
star-forming galaxies useful for comparison with studies at high redshifts. We
investigate the origin of the local benchmark gradient using simple chemical
evolution models and observed gas and stellar surface density profiles in
nearby field spiral galaxies. Our models suggest that the local benchmark
gradient is a direct result of the coevolution of gas and stellar disk under
virtually closed-box chemical evolution when the stellar-to-gas mass ratio
becomes high (>>0.3). These models imply low current mass accretion rates
(<0.3xSFR), and low mass outflow rates (<3xSFR) in local field star-forming
galaxies.Comment: 25 pages, 21 figures, accepted to MNRA
Warm Molecular Hydrogen in the Galactic Wind of M82
We report the detection of a complex of extraplanar warm H_2 knots and
filaments extending more than ~3 kpc above and below the galactic plane of M82,
roughly coincident with the well-known galactic wind in this system.
Comparisons of these data with published results at other wavelengths provide
quantitative constraints on the topology, excitation, heating, and stability
against disruption of the wind-entrained molecular ISM in this prototypical
galactic wind. Deep H_2 2.12 um observations such as these represent a
promising new method to study the elusive but potentially important molecular
component of galactic winds.Comment: Accepted for publication in the Astrophysical Journal Letters. Paper
with high-resolution figures is available at
http://www.astro.umd.edu/~veilleux/pubs/m82.pd
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