275 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
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
ISO observations of four active galaxies
We present ISO PHOT-S spectra of four galaxies known or suspected to host a
central AGN, selected from the initial Iras/Rosat sample of Boller et al.
(1992). Two of them had no obvious Seyfert features in their previous optical
spectra: IRAS 14201+2956, and IRAS 21582+1018. The latter was bright enough to
also allow SWS observations around selected neon lines, to establish its
excitation. While both PHOT-S spectra are characteristic of starburst-dominated
galaxies, the neon line ratios in IRAS 21582+1018 indicate the presence of a
hard excitation source. New, high-resolution, optical spectra show only a weak,
broad component around Halpha, classifying now these two objects as Sey 1.9
galaxies. The two other galaxies observed are the NLS1 galaxies Mrk 359 and Mrk
1388. Their ISO spectra however do not reveal the typical, strong PAH features
found in the starburst galaxies and are more like those of standard Seyferts.
These results show therefore that, although IR observations were expected to be
able to always reveal the presence of an active nucleus by piercing through the
central obscuration, the result may be ambiguous: the broad band IR energy
distribution can still be dominated by starburts located in a circumnuclear
region, and the AGN appear only in specific observations (high-excitation lines
in the IR, or optical spectra with better quality than classification spectra).
The obscuration needs however to be patchy rather than complete, to explain the
detection of the high-excitation lines or broad Balmer wings. Only high-energy
observations can then establish the strength of the central
AGN and the amount of extinction with certainty.Comment: 8 pages, 8 figures, accepted in Astronomy & Astrophysic
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
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