460 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
Redshifts from Spitzer Spectra for Optically Faint, Radio Selected Infrared Sources
Spectra have been obtained with the Infrared Spectrograph on the Spitzer
Space Telescope for 18 optically faint sources (R > 23.9,mag) having f(nu)
(24um) > 1.0,mJy and having radio detections at 20 cm to a limit of 115
microJy. Sources are within the Spitzer First Look Survey. Redshifts are
determined for 14 sources from strong silicate absorption features (12 sources)
or strong PAH emission features (2 sources), with median redshift of 2.1.
Results confirm that optically faint sources of ~1 mJy at 24um are typically at
redshifts z ~ 2, verifying the high efficiency in selecting high redshift
sources based on extreme infrared to optical flux ratio, and indicate that 24um
sources which also have radio counterparts are not systematically different
than samples chosen only by their infrared to optical flux ratios. Using the
parameter q = log[f(nu)(24um)/f(nu)(20 cm)] 17 of the 18 sources observed have
values of 0<q<1, in the range expected for starburst-powered sources, but only
a few of these show strong PAH emission as expected from starbursts, with the
remainder showing absorbed or power-law spectra consistent with an AGN
luminosity source. This confirms previous indications that optically faint
Spitzer sources with f(nu)(24um) > 1.0mJy are predominately AGN and represent
the upper end of the luminosity function of dusty sources at z ~ 2. Based on
the characteristics of the sources observed so far, we predict that the nature
of sources selected at 24um will change for f(nu)(24um) < 0.5 mJy to sources
dominated primarily by starbursts.Comment: Accepted ApJ 20 February 2006, v638 2 issue, 10pages including 3
figure
Morphological Classification of Local Luminous Infrared Galaxies
We present an analysis of the morphological classification of 89 luminous
infrared galaxies (LIRGs) from the Great Observatories All-sky LIRG Survey
(GOALS) sample using non-parametric coefficients and compare their morphology
as a function of wavelength. We rely on images obtained in the optical (B- and
I-band) as well as in the infrared (H-band and 5.8m). Our classification
is based on the calculation of and the second order of light ()
non-parametric coefficients which we explore as a function of stellar mass
(), infrared luminosity () and star formation rate (SFR). We
investigate the relation between , the specific SFR (sSFR) and the dust
temperature () in our galaxy sample. We find that is a
better morphological tracer than , as it allows to distinguish systems
formed by double systems from isolated and post-merger LIRGs. The
multi-wavelength analysis allows us to identify a region in the -
parameter space where ongoing mergers reside, regardless of the band used to
calculate the coefficients. In particular when measured in the H-band, this
region can be used to identify ongoing mergers, with a minimal contamination
from LIRGs in other stages. We also find that while the sSFR is positively
correlated with when measured in the mid-infrared, i.e. star-bursting
galaxies show more compact emission, it is anti-correlated with the B-band
based . We interpret this as the spatial decoupling between obscured
and un-obscured star formation, whereby the ultraviolet/optical size of a LIRGs
experience an intense dust enshrouded central starburst is larger than in the
one in the mid-infrared since the contrast between the nuclear to the extended
disk emission is smaller in the mid-infrared. This has important implications
for high redshift surveys of dusty sources. [abridged]Comment: ( 18 pages, 12 figures, Accepted for publication in A&A
The PEP Survey: Infrared Properties of Radio-Selected AGN
By exploiting the VLA-COSMOS and the Herschel-PEP surveys, we investigate the
Far Infrared (FIR) properties of radio-selected AGN. To this purpose, from
VLA-COSMOS we considered the 1537, F[1.4 GHz]>0.06 mJy sources with a reliable
redshift estimate, and sub-divided them into star-forming galaxies and AGN
solely on the basis of their radio luminosity. The AGN sample is complete with
respect to radio selection at all z<~3.5. 832 radio sources have a counterpart
in the PEP catalogue. 175 are AGN. Their redshift distribution closely
resembles that of the total radio-selected AGN population, and exhibits two
marked peaks at z~0.9 and z~2.5. We find that the probability for a
radio-selected AGN to be detected at FIR wavelengths is both a function of
radio power and redshift, whereby powerful sources are more likely to be FIR
emitters at earlier epochs. This is due to two distinct effects: 1) at all
radio luminosities, FIR activity monotonically increases with look-back time
and 2) radio activity of AGN origin is increasingly less effective at
inhibiting FIR emission. Radio-selected AGN with FIR emission are
preferentially located in galaxies which are smaller than those hosting
FIR-inactive sources. Furthermore, at all z<~2, there seems to be a
preferential (stellar) mass scale M ~[10^{10}-10^{11}] Msun which maximizes the
chances for FIR emission. We find such FIR (and MIR) emission to be due to
processes indistinguishable from those which power star-forming galaxies. It
follows that radio emission in at least 35% of the entire AGN population is the
sum of two contributions: AGN accretion and star-forming processes within the
host galaxy.Comment: 13 pages, 14 figures, to appear in MNRA
Utilisation des données SPOT pour la cartographie des ressources renouvelables : région méditerranéenne côtière, Nord-Ouest de l'Egypte : rapport final
Mid-infrared observations of the ultraluminous galaxies IRAS14348-1447, IRAS19254-7245, and IRAS23128-5919
We present a study of the three ultraluminous infrared galaxies
IRAS14348-1447, IRAS19254-7245, and IRAS23128-5919, based on mid-infrared (MIR)
spectro-imaging (5-18microns) observations performed with ISOCAM. We find that
the MIR emission from each system, which consists of a pair of interacting late
type galaxies, is principally confined to the nuclear regions with diameters of
1-2kpc and can account for more than 95% of their IRAS 12micron flux. In each
interacting system, the galaxy hosting an active galactic nucleus (AGN)
dominates the total spectrum and shows stronger dust continuum (12-16microns)
relative to the Unidentified Infrared Band (UIB) emission (6-9microns),
suggestive of its enhanced radiation field. The MIR dominant galaxy also
exhibits elevated 15micron/Halpha and 15micron/K ratios which trace the high
extinction due to the large quantities of molecular gas and dust present in its
central regions. Using only diagnostics based on our mid-infrared spectra, we
can establish that the Seyfert galaxy IRAS19254-7245 exhibits MIR spectral
features of an AGN while the MIR spectrum of the Seyfert (or LINER) member of
IRAS23128-5919 is characteristic of dust emission principally heated by star
forming regions.Comment: Accepted for publication in Astronomy & Astrophysics, 13 pages, 9
figure
New light on gamma-ray burst host galaxies with Herschel
Until recently, dust emission has been detected in very few host galaxies of
gamma-ray bursts (GRBHs). With Herschel, we have now observed 17 GRBHs up to
redshift z~3 and detected seven of them at infrared (IR) wavelengths. This
relatively high detection rate (41%) may be due to the composition of our
sample which at a median redshift of 1.1 is dominated by the hosts of dark
GRBs. Although the numbers are small, statistics suggest that dark GRBs are
more likely to be detected in the IR than their optically-bright counterparts.
Combining our IR data with optical, near-infrared, and radio data from our own
datasets and from the literature, we have constructed spectral energy
distributions (SEDs) which span up to 6 orders of magnitude in wavelength. By
fitting the SEDs, we have obtained stellar masses, dust masses, star-formation
rate (SFR), and extinctions for our sample galaxies. We find that GRBHs are
galaxies that tend to have a high specfic SFR (sSFR), and like other
star-forming galaxies, their ratios of dust-to-stellar mass are well correlated
with sSFR. We incorporate our Herschel sample into a larger compilation of
GRBHs, and compare this combined sample to SFR-weighted median stellar masses
of the widest, deepest galaxy survey to date. This is done in order to
establish whether or not GRBs can be used as an unbiased tracer of cosmic
comoving SFR density (SFRD) in the universe. In contrast with previous results,
this comparison shows that GRBHs are medium-sized galaxies with relatively high
sSFRs; stellar masses and sSFRs of GRBHs as a function of redshift are similar
to what is expected for star-forming galaxy populations at similar redshifts.
We conclude that there is no strong evidence that GRBs are biased tracers of
SFRD; thus they should be able to reliably probe the SFRD to early epochs.Comment: 18 pages, 9 figures, accepted for publication in A&A. Revised to
include Fig. 6, mistakenly omitted in origina
A Far-infrared Characterization of 24 μm Selected Galaxies at 0 < z < 2.5 using Stacking at 70 μm and 160 μm in the COSMOS Field
We present a study of the average properties of luminous infrared galaxies detected directly at 24 μm in the COSMOS field using a median stacking analysis at 70 μm and 160 μm. Over 35,000 sources spanning 0 ≤ z ≤ 3 and 0.06 mJy ≤ S_(24) ≤ 3.0 mJy are stacked, divided into bins of both photometric redshift and 24 μm flux. We find no correlation of S_(70)/S_(24) flux density ratio with S_(24), but find that galaxies with higher S_(24) have a lower S_(160)/S_(24) flux density ratio. These observed ratios suggest that 24 μm selected galaxies have warmer spectral energy distributions (SEDs) at higher mid-IR fluxes, and therefore have a possible higher fraction of active galactic nuclei. Comparisons of the average S_(70)/S_(24) and S_(160)/S_(24) colors with various empirical templates and theoretical models show that the galaxies detected at 24 μm are consistent with "normal" star-forming galaxies and warm mid-IR galaxies such as Mrk 231, but inconsistent with heavily obscured galaxies such as Arp 220. We perform a χ^2 analysis to determine best-fit galactic model SEDs and total IR luminosities for each of our bins. We compare our results to previous methods of estimating L IR and find that previous methods show considerable agreement over the full redshift range, except for the brightest S_(24) sources, where they overpredict the bolometric IR luminosity at high redshift, most likely due to their warmer dust SED. We present a table that can be used as a more accurate and robust method for estimating bolometric infrared luminosity from 24 μm flux densities
CO J=2-1 line emission in cluster galaxies at z~1: fueling star formation in dense environments
We present observations of CO J=2-1 line emission in infrared-luminous
cluster galaxies at z~1 using the IRAM Plateau de Bure Interferometer. Our two
primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie
within 2 Mpc of the centers of two massive (>10^14 Msun) galaxy clusters. CO
line emission is not detected in either DOG. We calculate 3-sigma upper limits
to the CO J=2-1 line luminosities, L'_CO < 6.08x10^9 and < 6.63x10^9 K km/s
pc^2. Assuming a CO-to-H_2 conversion factor derived for ultraluminous infrared
galaxies in the local Universe, this translates to limits on the cold molecular
gas mass of M_H_2 < 4.86x10^9 Msun and M_H_2 < 5.30x10^9 Msun. Both DOGs
exhibit mid-infrared continuum emission that follows a power-law, suggesting
that an AGN contributes to the dust heating. As such, estimates of the star
formation efficiencies in these DOGs are uncertain. A third cluster member with
an infrared luminosity, L_IR < 7.4x10^11 Lsun, is serendipitously detected in
CO J=2-1 line emission in the field of one of the DOGs located roughly two
virial radii away from the cluster center. The optical spectrum of this object
suggests that it is likely an obscured AGN, and the measured CO line luminosity
is L'_CO = (1.94 +/- 0.35)x10^10 K km/s pc^2, which leads to an estimated cold
molecular gas mass M_H_2 = (1.55+/-0.28)x10^10 Msun. A significant reservoir of
molecular gas in a z~1 galaxy located away from the cluster center demonstrates
that the fuel can exist to drive an increase in star-formation and AGN activity
at the outskirts of high-redshift clusters.Comment: 22 pages, 4 figures; accepted for publication in Ap
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