7,366 research outputs found
The Most Luminous Galaxies
Ultraluminous galaxies in the local universe (z0.2) emit the bulk of
their energy in the mid and far-infrared. The multiwavelength approach to these
objects has shown that they are advanced mergers of gas-rich spiral galaxies.
Galaxy-galaxy collisions took place on all cosmological time-scales, and nearby
mergers serve as local analogs to gain insight into the physical processes that
lead to the formation and trans-formation of galaxies in the more distant
universe. Here I review multiwavelength observations --with particular emphasis
on recent results obtained with ISO-- of mergers of massive galaxies driving
the formation of: 1) luminous infrared galaxies, 2) elliptical galaxy cores, 3)
luminous dust-enshrouded extranuclear starbursts, 4) symbiotic galaxies that
host AGNs, and 5) tidal dwarf galaxies. The most important implication for
studies on the formation of galaxies at early cosmological timescales is that
the distant analogs to the local ultraluminous infrared galaxies are invisible
in the ultraviolet and optical wavelength rest-frames and should be detected as
sub-millimeter sources with no optical counterparts.Comment: 12 pages, 6 figures. Invited Review at the Conference Lighthouses of
the universe. August 6-10, 2001 (Garching, Germany
Spectroscopic Redshifts to z > 2 for Optically Obscured Sources Discovered with the Spitzer Space Telescope
We have surveyed a field covering 9.0 degrees^2 within the NOAO Deep
Wide-Field Survey region in Bootes with the Multiband Imaging Photometer on the
Spitzer Space Telescope (SST) to a limiting 24 um flux density of 0.3 mJy.
Thirty one sources from this survey with F(24um) > 0.75 mJy which are optically
very faint (R > 24.5 mag) have been observed with the low-resolution modules of
the Infrared Spectrograph on SST. Redshifts derived primarily from strong
silicate absorption features are reported here for 17 of these sources; 10 of
these are optically invisible (R > 26 mag), with no counterpart in B_W, R, or
I. The observed redshifts for 16 sources are 1.7 < z < 2.8. These represent a
newly discovered population of highly obscured sources at high redshift with
extreme infrared to optical ratios. Using IRS spectra of local galaxies as
templates, we find that a majority of the sources have mid-infrared spectral
shapes most similar to ultraluminous infrared galaxies powered primarily by
AGN. Assuming the same templates also apply at longer wavelengths, bolometric
luminosities exceed 10^13 L(solar).Comment: Accepted for publication on 7 Feb 2005 in ApJL. 7 pages 2 figure
Formation of Molecular Gas in the debris of violent Galaxy Interactions
In many gravitational interactions between galaxies, gas and stars that have
been torn from either or both of the precursor galaxies can collect in 'tidal
tails'. Star formation begins anew in these regions to produce 'tidal dwarf
galaxies', giving insight into the process of galaxy formation through the
well-defined timescale of the interaction. But tracking the star formation
process has proved to be difficult: the tidal dwarf galaxies with young stars
showed no evidence of the molecular gas out of which new stars form. Here we
report the discovery of molecular gas (carbon monoxide emission) in two tidal
dwarf galaxies. In both cases, the molecular gas peaks at the same location as
the maximum in atomic-hydrogen density, unlike most gas-rich galaxies. We infer
from this that the molecular gas formed from the HI, rather than being torn in
molecular form from the interacting galaxies. Star formation in the tidal
dwarfs appears to mimic that process in normal spiral galaxies like our own.Comment: 8 pages, 3 figures, Nature in pres
Black hole in the West Nucleus of Arp 220
We present new observations with the IRAM Interferometer, in its
longest-baseline configuration, of the CO(2-1) line and the 1.3mm dust
radiation from the Arp 220 nuclear region. The dust source in the West nucleus
has a size of 0.19 x 0.13 arcsec and a 1.3mm brightness temperature of 90K.
This implies that the dust ring in the West nucleus has a high opacity, with
tau = 1 at 1.1mm. Not only is the dust ring itself optically thick in the submm
and far-IR, but it is surrounded by the previously-known, rapidly rotating
molecular disk of size 0.5 arcsec that is also optically thick in the mid-IR.
The molecular ring is cooler than the hot dust disk because the CO(2-1) line is
seen in absorption against the dust disk. The dust ring is massive (1E9 solar
masses), compact (radius 35pc), and hot (true dust temperature 170K). It
resembles rather strikingly the dust ring detected around the quasar APM
08279+52, and is most unlike the warm, extended dust sources in starburst
galaxies. Because there is a strong temperature gradient from the hot dust ring
to the cooler molecular disk, the heating must come from a concentrated source,
an AGN accretion disk that is completely invisible at optical wavelengths, and
heavily obscured in hard X-rays.Comment: Reference list updated for 2007 publications; estimated position
errors increase
A bias in optical observations of high redshift luminous infrared galaxies
We present evidence for the dramatically different morphology between the
rest frame UV and 7micron mid-IR emission of VV114 and Arp299, two nearby (z~0)
violently interacting infrared luminous galaxies (LIRGs). Nearly all LIRGs are
interacting systems and it is currently accepted that they dominate the IR
emission at z>1. Luminous IR galaxies located at z=1-2 could easily be detected
as unresolved sources in deep optical/near-IR ground based surveys, as well as
in upcoming 24micron surveys with the Space Infrared Telescope Facility. We
demonstrate that the spatial resolution of these surveys will result in
blending of the emission from unresolved interacting components. An increased
scatter will thus be introduced in the observed optical to mid-IR colors of
these galaxies, leading to a systematic underestimation of their dust content.Comment: To appear in the Astrophysical Journal Letters (4 pages 1 figure
- …