28 research outputs found
Extremely Red Objects in the Field of QSO 1213-0017: A Galaxy Concentration at z=1.31
We have discovered a concentration of extremely red objects (EROs; R-K>6) in
the field of the z=2.69 quasar QSO 1213-0017 (UM 485), which is significantly
overabundant compared to the field ERO surface density. The optical/near-IR
colors of the EROs and numerous other red galaxies in this field are consistent
with elliptical galaxies at z=1-2. HST optical images for a subset of galaxies
show regular morphologies, most of them being disky or diffuse and without any
obvious evidence for interactions. Ground-based IR images show similar
morphologies, indicating any dust reddening in these objects is spatially
uniform. Optical spectroscopy with the W. M. Keck Telescope has found that four
of the red galaxies lie at =1.31, and a fifth lies in the foreground at
z=1.20. Of the =1.31 galaxies, one is a reddened AGN while the remaining
three have rest-frame UV absorption-line spectra characteristic of old (few
Gyr) stellar populations, similar to the old red galaxy LBDS 53W091 at z=1.55.
Including the MgII absorber seen in the QSO spectrum, we find five galaxies at
=1.31 spread over 1.5 h_50^{-1} Mpc on the sky. These results suggest we
have discovered a coherent structure of old galaxies at high-redshift, possibly
associated with a massive galaxy cluster.Comment: 37 pages including 11 Postscript figures. To appear in the June 2000
issue of the Astronomical Journa
Ongoing Formation of Bulges and Black Holes in the Local Universe: New Insights from GALEX
We analyze a volume-limited sample of massive bulge-dominated galaxies with
data from both the Sloan Digital Sky Survey and the Galaxy Evolution Explorer
(GALEX) satellite. The galaxies have central velocity dispersions greater than
100 km/s and stellar surface mass densities that lie above the value where
galaxies transition from actively star forming to passive systems. The sample
is limited to redshifts 0.03<z<0.07. At these distances, the SDSS spectra
sample the light from the bulge-dominated central regions of the galaxies. The
GALEX NUV data provide high sensitivity to low rates of global star formation
in these systems. Our sample of bulge-dominated galaxies exhibits a much larger
dispersion in NUV-r colour than in optical g-r colour. Nearly all of the
galaxies with bluer NUV-r colours are AGN. Both GALEX images and SDSS colour
profiles demonstrate that the excess UV light is associated with an extended
disk. We find that galaxies with red outer regions almost never have a young
bulge or a strong AGN. Galaxies with blue outer regions have bulges and black
holes that span a wide range in age and accretion rate. Galaxies with young
bulges and strongly accreting black holes almost always have blue outer disks.
Our suggested scenario is one in which the source of gas that builds the bulge
and black hole is a low mass reservoir of cold gas in the disk.The presence of
this gas is a necessary, but not sufficient condition for bulge and black hole
growth. Some mechanism must transport this gas inwards in a time variable way.
As the gas in the disk is converted into stars, the galaxies will turn red, but
further gas infall can bring them back into the blue NUV-r sequence.(Abridged)Comment: 34 pages, 16 figures. Accepted for the GALEX special issue of ApJ
The Diverse Properties of the Most Ultraviolet Luminous Galaxies Discovered by the Galaxy Evolution Explorer
We report on the properties of a sample of ultraviolet luminous galaxies
(UVLGs) selected by matching the Galaxy Evolution Explorer (GALEX) Surveys with
the Sloan Digital Sky Survey Third Data Release. Out of 25362 galaxies between
0.02x10^10 L_solar at
1530 Angstroms (observed wavelength). The properties of this population are
well correlated with ultraviolet surface brightness. We find that the galaxies
with low UV surface brightness are primarily large spiral systems with a
mixture of old and young stellar populations, while the high surface brightness
galaxies consist primarily of compact starburst systems. In terms of the
behavior of surface brightness with luminosity, size with luminosity, the
mass-metallicity relation, and other parameters, the compact UVLGs clearly
depart from the trends established by the full sample of galaxies. The subset
of compact UVLGs with the highest surface brightness (``supercompact UVLGs'')
have characteristics that are remarkably similar to Lyman Break Galaxies at
higher redshift. They are much more luminous than typical local
ultraviolet-bright starburst galaxies and blue compact dwarf galaxies. They
have metallicities that are systematically lower than normal galaxies of the
same stellar mass, indicating that they are less chemically evolved. In all
these respects, they are the best local analogs for Lyman Break Galaxies.Comment: Fixed error in ObjID column of Table 1. 30 pages, 12 figures.
Accepted for the GALEX special issue of ApJS. Abstract abridge
The DEEP2 Galaxy Redshift Survey: Spectral classification of galaxies at z~1
We present a Principal Component Analysis (PCA)-based spectral
classification, eta, for the first 5600 galaxies observed in the DEEP2 Redshift
Survey. This parameter provides a very pronounced separation between absorption
and emission dominated galaxy spectra - corresponding to passively evolving and
actively star-forming galaxies in the survey respectively. In addition it is
shown that despite the high resolution of the observed spectra, this parameter
alone can be used to quite accurately reconstruct any given galaxy spectrum,
suggesting there are not many `degrees of freedom' in the observed spectra of
this galaxy population. It is argued that this form of classification, eta,
will be particularly valuable in making future comparisons between high and
low-redshift galaxy surveys for which very large spectroscopic samples are now
readily available, particularly when used in conjunction with high-resolution
spectral synthesis models which will be made public in the near future. We also
discuss the relative advantages of this approach to distant galaxy
classification compared to other methods such as colors and morphologies.
Finally, we compare the classification derived here with that adopted for the
2dF Galaxy Redshift Survey and in so doing show that the two systems are very
similar. This will be particularly useful in subsequent analyses when making
comparisons between results from each of these surveys to study evolution in
the galaxy populations and large-scale structure.Comment: 10 pages, 9 figures, Accepted for publication in Ap
The UV-Optical Color Magnitude Diagram II: Physical Properties and Morphological Evolution On and Off of a Star-Forming Sequence
We use the UV-optical color magnitude diagram in combination with
spectroscopic and photometric measurements derived from the SDSS spectroscopic
sample to measure the distribution of galaxies in the local universe (z<0.25)
and their physical properties as a function of specific star formation rate
(SSFR) and stellar mass. Throughout this study our emphasis is on the
properties of galaxies on and off of a local "star-forming sequence." We
discuss how the physical characteristics of galaxies along this sequence are
related to scaling relations typically derived for galaxies of different
morphological types. We find, among other trends that our measure of the star
formation rate surface density is nearly constant along this sequence. We
discuss this result and implications for galaxies at higher redshift. For the
first time, we report on measurements of the local UV luminosity function
versus galaxy structural parameters as well as inclination. We also split our
sample into disk-dominated and bulge-dominated subsamples using the i-band
Sersic index and find that disk-dominated galaxies occupy a very tight locus in
SSFR vs. stellar mass space while bulge-dominated galaxies display a much
larger spread of SSFR at fixed stellar mass. A significant fraction of galaxies
with SSFR and SF surface density above those on the "star-forming sequence" are
bulge-dominated. We can use our derived distribution functions to ask whether a
significant fraction of these galaxies may be experiencing a final episode of
star formation (possibly induced by a merger or other burst), soon to be
quenched, by determining whether this population can explain the growth rate of
the non-star-forming galaxies on the "red sequence." (Abridged)Comment: 30 pages, 28 figures, scheduled to appear as part of the GALEX
Special Ap.J.Suppl., December, 2007 (29 papers
The First Data Release of the Sloan Digital Sky Survey
The Sloan Digital Sky Survey has validated and made publicly available its
First Data Release. This consists of 2099 square degrees of five-band (u, g, r,
i, z) imaging data, 186,240 spectra of galaxies, quasars, stars and calibrating
blank sky patches selected over 1360 square degrees of this area, and tables of
measured parameters from these data. The imaging data go to a depth of r ~ 22.6
and are photometrically and astrometrically calibrated to 2% rms and 100
milli-arcsec rms per coordinate, respectively. The spectra cover the range
3800--9200 A, with a resolution of 1800--2100. Further characteristics of the
data are described, as are the data products themselves.Comment: Submitted to The Astronomical Journal. 16 pages. For associated
documentation, see http://www.sdss.org/dr
The Properties of Ultraviolet-Luminous Galaxies at the Current Epoch
We have used the first matched set of GALEX and SDSS data to investigate the properties of a sample of 74 nearby galaxies with far-ultraviolet luminosities chosen to overlap the luminosity range of typical high-z Lyman Break Galaxies (LBGs). GALEX deep surveys have shown that ultraviolet-luminous galaxies (UVLGs) similar to these are the fastest evolving component of the UV galaxy population. Model fits to the combined GALEX and SDSS photometry yield typical FUV extinctions similar to LBGs. The implied star formation rates are SFR ~ 3 to 30 solar mass per year. This overlaps the range of SFRs for LBGs. We find a strong inverse correlation between galaxy mass and far-ultraviolet surface brightness, and on this basis divide the sample into ``large\'\' and ``compact\'\' UVLGs. The compact UVLGs have half-light radii of a few kpc or less (similar to LBGs). They are relatively low mass galaxies (~10 billion solar masses) with typical velocity dispersions of 60 to 150 km/s. They span a range in metallicity from 0.3 to 1 times solar, have blue optical-UV colors, and are forming stars at a rate sufficient to build the present galaxy in ~a Gigayear. In all these respects they appear similar to the LBG population. These ``living fossils\'\' may therefore provide an opportunity for detailed investigation of the physical processes occurring in typical star forming galaxies in the early universe