104 research outputs found
The Evolution of Early-Type Galaxies in Distant Clusters
We present results from an optical-IR photometric study of early-type
galaxies in 19 galaxy clusters out to z=0.9. The galaxy sample is selected on
the basis of morphologies determined from HST WFPC2 images, and is
photometrically defined in the K-band to minimize redshift-dependent selection
biases. The optical-IR colors of the early-type cluster galaxies become bluer
with increasing redshift in a manner consistent with the passive evolution of
an old stellar population formed at an early cosmic epoch. The degree of color
evolution is similar for clusters at similar redshift, and does not depend
strongly on the optical richness or X-ray luminosity of the cluster, suggesting
that the history of early-type galaxies is relatively insensitive to
environment. The slope of the color-magnitude relationship shows no significant
change out to z=0.9, providing evidence that it arises from a correlation
between galaxy mass and metallicity, not age. Finally, the intrinsic scatter in
the optical-IR colors is small and nearly constant with redshift, indicating
that the majority of giant, early-type galaxies in clusters share a common star
formation history, with little perturbation due to uncorrelated episodes of
later star formation. Taken together, our results are consistent with models in
which most early-type galaxies in rich clusters are old, formed the majority of
their stars at high redshift in a well-synchronized fashion, and evolved
quiescently thereafter.Comment: 55 pages, 24 figures, uses AASTeX. Accepted for publication in The
Astrophysical Journa
The Sloan Digital Sky Survey: The Cosmic Spectrum and Star-Formation History
We present a determination of the `Cosmic Optical Spectrum' of the Universe,
i.e. the ensemble emission from galaxies, as determined from the red-selected
Sloan Digital Sky Survey main galaxy sample and compare with previous results
of the blue-selected 2dF Galaxy Redshift Survey. Broadly we find good agreement
in both the spectrum and the derived star-formation histories. If we use a
power-law star-formation history model where star-formation rate out to z=1, then we find that of 2 to 3 is still the most
likely model and there is no evidence for current surveys missing large amounts
of star formation at high redshift. In particular `Fossil Cosmology' of the
local universe gives measures of star-formation history which are consistent
with direct observations at high redshift. Using the photometry of SDSS we are
able to derive the cosmic spectrum in absolute units (i.e.^{-1}^{-3}\Msun/\Lsun\omstars h = 0.0025\alpha\Msun^{-1}^{-3}$ today.Comment: 17 pages, 11 figures, ApJ in press (April 10th 2003
An ultraviolet-selected galaxy redshift survey - III: Multicolour imaging and non-uniform star formation histories
(abridged) We present panoramic u' and optical ground-based imaging
observations of a complete sample of low-redshift (0<z<0.4) galaxies selected
in the ultraviolet (UV) at 2000A using the balloon-borne FOCA instrument of
Milliard et al. This survey is highly sensitive to newly-formed massive stars,
and hence to actively star-forming galaxies. We use the new data to further
investigate the stellar population and star formation properties of this
sample. When combined with our earlier spectroscopic surveys, these new data
allow us to compare star-formation measures derived from aperture-corrected Ha
line fluxes, UV(2000A) and u'(3600A) continuum fluxes on a galaxy-by-galaxy
basis. As expected from our earlier studies, we find broad correlations between
the dust-corrected star-formation diagnostics, though the scatter is larger
than that from observational errors, with significant offsets from trends
expected according to simple star-formation history (SFH) models. Varying
metallicities and/or initial mass functions seem unable to explain the observed
discrepancies. We investigate the star-formation properties further by
modelling the observed spectroscopic and photometric properties of the galaxies
in our survey. Nearly half of the galaxies surveyed possess features that
appear incompatible with simple constant or smoothly declining SFHs, favouring
instead irregular or temporally-varying SFHs. We demonstrate how this can
reconcile the majority of our observations, and determine empirical corrections
to calculate intrinsic star formation rates from measures based on UV (or u')
observations alone. We discuss the broader implications of our finding that a
significant fraction of star-forming galaxies have complex SFHs, particularly
in the context of recent determinations of the cosmic SFH.Comment: MNRAS; post-referee report version. 16 pages, 10 figure
The Morphological Diversities Among Star-forming Galaxies at High Redshifts in the Great Observatories Origins Deep Survey (GOODS)
We have used the HST/ACS images to identify 4700 Lyman break galaxies (LBGs)
in GOODS. We present the results from a parametric analysis of the 2-D surface
brightness profiles, for 1333 LBGs at z > 2.5 with rest-frame UV(1600 Angstrom)
AB magnitude < -20.5. Based on the Sersic index, n, which measures the profile
shape, we find that about 40% of LBGs at z=3 have light profiles close to
exponential, and only 30% have the high concentrations seen for spheroids.
About 30% of LBGs appear to have multiple cores or disturbed morphologies
suggestive of close pairs or on-going mergers. The fraction of spheroid-like (n
> 2.5) LBGs decreases by about 15% from z = 5 to 3. A comparison of LBGs with
the starburst galaxies at z = 1.2, shows that the fraction of spheroid-like
profiles is about 20% higher among LBGs. The ellipticity distribution for LBGs
exhibits a pronounced skew towards high ellipticities (> 0.5), which cannot be
explained by morphologies similar to the local disks and spheroids viewed at
random orientations. The peak of the distribution evolves toward lower
ellipticities, from 0.7 at z = 4 to 0.5 at z = 3. At z = 1.2 the distribution
is relatively flat as seen among the present-day galaxies. The dominance of
elongated morphologies among LBGs suggests that in a significant fraction of
them we may be witnessing star-formation in clumps along gas-rich filaments, or
the earliest gas-rich bars that encompass essentially the entire visible
galaxy. Similar features are found to be ubiquitous in hydrodynamical
simulations in which galaxy formation at high redshifts occurs in filamentary
inflows of dynamically cold gas within the dark matter halos, and involves gas-
rich mergers.Comment: Accepted for publication in the Astrophysical Journal (10 October,
2006 issue), 15 pages + 12 JPEG figure
The Performance and Scientific Rationale for an IR Imaging Fourier Transform Spectrograph on a Large Space Telescope
We describe a concept for an imaging spectrograph for a large orbiting
observatory such as NASA's proposed Next Generation Space Telescope (NGST)
based on an imaging Fourier transform spectrograph (IFTS). An IFTS has several
important advantages which make it an ideal instrument to pursue the scientific
objectives of NGST. We review the operation of an IFTS and make a quantitative
evaluation of the signal-to-noise performance of such an instrument in the
context of NGST. We consider the relationship between pixel size, spectral
resolution, and diameter of the beamsplitter for imaging and non-imaging
Fourier transform spectrographs and give the condition required to maintain
spectral modulation efficiency over the entire field of view. We give examples
of scientific programs that could be performed with this facility.Comment: 20 pages, 7 Postscript figures. PASP in pres
KURVS: The outer rotation curve shapes and dark matter fractions of star-forming galaxies
We present first results from the KMOS Ultra-deep Rotation Velocity Survey
(KURVS), aimed at studying the outer rotation curves shape and dark matter
content of 22 star-forming galaxies at . These galaxies represent
`typical' star-forming discs at , being located within the
star-forming main sequence and stellar mass-size relation with stellar masses
log. We extract
individual rotation curves out to 4 times the effective radius, on average, or
kpc. Most rotation curves are flat or rising between three- and
six-disc scale radii. Only three objects with dispersion-dominated dynamics
() have declining outer rotation curves at more
than 5 significance. After accounting for seeing and pressure support,
the nine rotation-dominated discs with have
average dark matter fractions of at the effective radius, similar
to local discs. Together with previous observations of star-forming galaxies at
cosmic noon, our measurements suggest a trend of declining dark matter fraction
with increasing stellar mass and stellar mass surface density at the effective
radius. Simulated EAGLE galaxies are in quantitative agreement with
observations up to log, and over-predict the dark matter fraction of galaxies with higher
mass surface densities by a factor of . We conclude that the dynamics
of typical rotationally-supported discs at is dominated by dark
matter from effective radius scales, in broad agreement with cosmological
models. The tension with observations at high stellar mass surface density
suggests that the prescriptions for baryonic processes occurring in the most
massive galaxies (such as bulge growth and quenching) need to be reassessed.Comment: 23 pages, 9 figures. Resubmitted to MNRAS after addressing the
referee's comments. Abstract slightly modified to compile with the arXiv
formattin
The Hubble Space Telescope Wide Field Camera 3 Early Release Science data: Panchromatic Faint Object Counts for 0.2-2 microns wavelength
We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early
Release Science (ERS) observations in the Great Observatories Origins Deep
Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled
mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR
filters F098M (Ys), F125W (J), and F160W (H) with 1-2 HST orbits per filter.
Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South
mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50
square arcmin at 0.2-1.7 {\mu}m in wavelength at 0.07-0.15" FWHM resolution and
0.090" Multidrizzled pixels to depths of AB\simeq 26.0-27.0 mag (5-{\sigma})
for point sources, and AB\simeq 25.5-26.5 mag for compact galaxies.
In this paper, we describe: a) the scientific rationale, and the data taking
plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the
procedure of generating object catalogs across the 10 different ERS filters,
and the specific star-galaxy separation techniques used; and c) the reliability
and completeness of the object catalogs from the WFC3 ERS mosaics. The
excellent 0.07-0.15" FWHM resolution of HST/WFC3 and ACS makes star- galaxy
separation straightforward over a factor of 10 in wavelength to AB\simeq 25-26
mag from the UV to the near-IR, respectively.Comment: 51 pages, 71 figures Accepted to ApJS 2011.01.2
The Fifth Data Release of the Sloan Digital Sky Survey
This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky
Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and
represents the completion of the SDSS-I project (whose successor, SDSS-II will
continue through mid-2008). It includes five-band photometric data for 217
million objects selected over 8000 square degrees, and 1,048,960 spectra of
galaxies, quasars, and stars selected from 5713 square degrees of that imaging
data. These numbers represent a roughly 20% increment over those of the Fourth
Data Release; all the data from previous data releases are included in the
present release. In addition to "standard" SDSS observations, DR5 includes
repeat scans of the southern equatorial stripe, imaging scans across M31 and
the core of the Perseus cluster of galaxies, and the first spectroscopic data
from SEGUE, a survey to explore the kinematics and chemical evolution of the
Galaxy. The catalog database incorporates several new features, including
photometric redshifts of galaxies, tables of matched objects in overlap regions
of the imaging survey, and tools that allow precise computations of survey
geometry for statistical investigations.Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS
Sixth Data Release (DR6) is now public, available from http://www.sdss.or
Observing Galaxy Evolution in the Context of Large-Scale Structure
Galaxies form and evolve in the context of their local and large-scale
environments. Their baryonic content that we observe with imaging and
spectroscopy is intimately connected to the properties of their dark matter
halos, and to their location in the "cosmic web" of large-scale structure. Very
large spectroscopic surveys of the local universe (e.g., SDSS and GAMA) measure
galaxy positions (location within large-scale structure), statistical
clustering (a direct constraint on dark matter halo masses), and spectral
features (measuring physical conditions of the gas and stars within the
galaxies, as well as internal velocities). Deep surveys with the James Webb
Space Telescope (JWST) will revolutionize spectroscopic measurements of
redshifts and spectral properties for galaxies out to the epoch of
reionization, but with numerical statistics and over cosmic volumes that are
too small to map large-scale structure and to constrain halo properties via
clustering. Here, we consider advances in understanding galaxy evolution that
would be enabled by very large spectroscopic surveys at high redshifts: very
large numbers of galaxies (outstanding statistics) over large co-moving volumes
(large-scale structure on all scales) over broad redshift ranges (evolution
over most of cosmic history). The required observational facility can be
established as part of the probe portfolio by NASA within the next decade.Comment: 8 pages (including cover page and references), 3 figures. Science
white paper submitted to Astro2020. arXiv admin note: substantial text
overlap with arXiv:1802.0153
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