825 research outputs found
Clustering of red Galaxies near the Radio-loud Quasar 1335.8+2834 at z=1.1
We have obtained new deep optical and near-infrared images of the field of
the radio-loud quasar 1335.8+2834 at where an excess in the surface
number density of galaxies was reported by Hutchings et al. [AJ, 106, 1324]
from optical data. We found a significant clustering of objects with very red
optical-near infrared colors, and near the quasar. The colors and magnitudes of the reddest objects
are consistent with those of old (12 Gyr old at z=0) passively-evolving
elliptical galaxies seen at , clearly defining a `red envelope' like
that found in galaxy clusters at similar or lower redshifts. This evidence
strongly suggests that the quasar resides in a moderately-rich cluster of
galaxies (richness-class ). There is also a relatively large fraction
of objects with moderately red colors () which have a
distribution on the sky similar to that of the reddest objects. They may be
interpreted as cluster galaxies with some recent or on-going star formation.Comment: 14 pages text, 5 PostScript figures, 1 GIF figure, and 1 combined PS
file. Accepted for ApJ, Letter
A Rich Cluster of Galaxies Near the Quasar B2 1335+28 at z=1.1: Color Distribution and Star-Formation Properties
We previously reported a significant clustering of red galaxies (R-K=3.5--6)
around the radio-loud quasar B2 1335+28 at z=1.086. In this paper, we establish
the existence of a rich cluster at the quasar redshift, and study the
properties of the cluster galaxies through further detailed analysis of the
photometric data. The color distribution of the galaxies in the cluster is
quite broad and the fraction of blue galaxies (\sim 70%) is much larger than in
intermediate-redshift clusters. Using evolutionary synthesis models, we show
that this color distribution can be explained by galaxies with various amounts
of star-formation activity mixed with the old stellar populations. Notably,
there are about a dozen galaxies which show very red optical-NIR colors but
also show significant UV excess with respect to passive-evolution models. They
can be interpreted as old early-type galaxies with a small amount of star
formation. The fact that the UV-excess red galaxies are more abundant than the
quiescent red ones suggests that a large fraction of old galaxies in this
cluster are still forming stars to some extent. However, a sequence of
quiescent red galaxies is clearly identified on the R-K versus K
color-magnitude (C-M) diagram. The slope and zero point of their C-M relation
appear to be consistent with those expected for the precursors of the C-M
relation of present-day cluster ellipticals when observed at z=1.1. We estimate
the Abell richness class of the cluster to be R \sim 1. New X-ray data
presented here place an upper limit of L_x < 2 10^{44} erg s^{-1} for the
cluster luminosity. Inspections of the wider optical images reveal some lumpy
structure, suggesting that the whole system is still dynamically young.Comment: 54 pages including 13 Postscript figures, 1 jpg figure, and 1 table,
uses aasms4.sty and epsf.sty. Accepted for publication in ApJ: Replaced as
the older verison was missed to include the figure 2c, 2d, and figure
B3 0003+387: AGN Marked Large-Scale Structure at z=1.47?
We present evidence for a significant overdensity of red galaxies, as much as
a factor of 14 over comparable field samples, in the field of the z=1.47 radio
galaxy B3 0003+387. The colors and luminosities of the brightest red galaxies
are consistent with their being at z>0.8. The radio galaxy and one of the red
galaxies are separated by 5" and show some evidence of a possible interaction.
However, the red galaxies do not show any strong clustering around the radio
galaxy nor around any of the brighter red galaxies. The data suggest that we
are looking at a wall or sheet of galaxies, possibly associated with the radio
galaxy at z=1.47. Spectroscopic redshifts of these red galaxies will be
necessary to confirm this large-scale structure.Comment: 19 pages, 7 figures, LaTeX2e/AASTeX v5.0.2. The full photometric
catalog is included as a separate deluxetable file. To appear in the
Astronomical Journal (~Nov 00
Cooling Flow Star Formation and the Apparent Stellar Ages of Elliptical Galaxies
Observational constraints and theoretical arguments indicate that cooled
interstellar gas in bright elliptical galaxies forms into a young stellar
population throughout the region within the half-light radius. The young
population has a bottom-heavy, but optically luminous IMF extending to 1 - 2
M_sun. When the colors and spectral features of this young population are
combined with those of the underlying old stellar population, the apparent ages
are significantly reduced, similar to the relatively young apparent ages
observed in many ellipticals. Galactic mergers are not required to resupply
young stars. The sensitivity of continuous star formation to L_B and L_x/L_B is
likely to account for the observed spread in apparent ages among elliptical
galaxies. Local star formation is accompanied by enhanced stellar H_beta
equivalent widths, stronger optical emission lines, enhanced thermal X-ray
emission and lower apparent temperatures in the hot gas. The young stars should
cause M/L to vary with galactic radius, perturbing the fundamental plane
occupied by the old stars.Comment: 6 pages with 2 figures; accepted by Astrophysical Journal Letter
Cluster Galaxy Evolution from a New Sample of Galaxy Clusters at 0.3 < z < 0.9
(Abridged) We analyze photometry and spectroscopy of a sample of 63 clusters
at 0.3<z<0.9 drawn from the Las Campanas Distant Cluster Survey to empirically
constrain models of cluster galaxy evolution. Specifically, by combining data
on our clusters with those from the literature we parametrize the redshift
dependence of 1) M*_I in the observed frame; 2) the V-I color of the E/S0 red
sequence in the observed frames; and 3) the I-K' color of the E/S0 red sequence
in the observed frame. Using the peak surface brightness of the cluster
detection, S, as a proxy for cluster mass, we find no correlation between S and
M* or the location of the red envelope in V-I. We suggest that these
observations can be explained with a model in which luminous early type
galaxies (or more precisely, the progenitors of current day luminous early type
galaxies) form the bulk of their stellar populations at high redshift (>~ 5)
and in which many of these galaxies, if not all, accrete mass either in the
form of evolved stellar populations or gas that causes only a short term
episode of star formation at lower redshifts (1.5 < z < 2). Our data are too
crude to reach conclusions regarding the evolutionary state of any particular
cluster or to investigate whether the morphological evolution of galaxies
matches the simple scenario we discuss, but the statistical nature of this
study suggests that the observed evolutionary trends are universal in massive
clusters.Comment: 35 pages, accepted for publication in Ap
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
HST Photometry and Keck Spectroscopy of the Rich Cluster MS1054-03: Morphologies, Butcher-Oemler Effect and the Color-Magnitude Relation at z=0.83
We present a study of 81 I selected, spectroscopically-confirmed members of
the X-ray cluster MS1054-03 at z=0.83. Redshifts and spectral types were
determined from Keck spectroscopy. Morphologies and accurate colors were
determined from a large mosaic of HST WFPC2 images in F606W and F814W.
Early-type galaxies constitute only 44% of this galaxy population. Thirty-nine
percent are spiral galaxies, and 17% are mergers. The early-type galaxies
follow a tight and well-defined color-magnitude relation, with the exception of
a few outliers. The observed scatter is 0.029 +- 0.005 magnitudes in restframe
U-B. Most of the mergers lie close to the CM relation defined by the early-type
galaxies. They are bluer by only 0.07 +- 0.02 magnitudes, and the scatter in
their colors is 0.07 +- 0.04 magnitudes. Spiral galaxies in MS1054-03 exhibit a
large range in their colors. The bluest spiral galaxies are 0.7 magnitudes
bluer than the early-type galaxies, but the majority is within +- 0.2
magnitudes of the early-type galaxy sequence. The red colors of the mergers and
the majority of the spiral galaxies are reflected in the fairly low
Butcher-Oemler blue fraction of MS1054-03: f_B=0.22 +- 0.05. The slope and
scatter of the CM relation of early-type galaxies are roughly constant with
redshift, confirming previous studies that were based on ground-based color
measurements and very limited membership information. However, the scatter in
the combined sample of early-type galaxies and mergers is twice as high as the
scatter of the early-type galaxies alone. This is a direct demonstration of the
``progenitor bias'': high redshift early-type galaxies seem to form a
homogeneous, old population because the progenitors of the youngest present-day
early-type galaxies are not included in the sample.Comment: Accepted for publication in the ApJ. At
http://astro.caltech.edu/~pgd/cm1054/ color figures can be obtaine
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 Number Density of Old Passively-Evolving Galaxies at z=1 in the Subaru/XMM-Newton Deep Survey Field
We obtained the number counts and the rest-frame B-band luminosity function
of the color-selected old passively-evolving galaxies (OPEGs) at z=1 with very
high statistical accuracy using a large and homogeneous sample of about 4000
such objects with z' <25 detected in the area of 1.03 deg^2 in the
Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined
on the i'-z' and R-z' color-magnitude plane so that OPEGs at z=0.9-1.1 with
formation redshift z_f=2-10 are properly sampled. The limiting magnitude
corresponds to the luminosity of galaxies with M_*+3 at z=0. We made a pilot
redshift observations for 99 OPEG candidates with 19 < z' < 22 and found that
at least 78% (73/93) of the entire sample, or 95% (73/77) of these whose
redshifts were obtained are indeed lie between z=0.87 and 1.12 and the most of
their spectra show the continuum break and strong Ca H and K lines, indicating
that these objects are indeed dominated by the old stellar populations. We then
compare our results with the luminosity functions of the color- or the
morphologically-selected early type galaxies at z=0 taking the evolutionary
factor into account and found that the number density of old passive galaxies
with sim M_* magnitude at z~1 averaged over the SXDS area is 40-60% of the
equivalently red galaxies and 60-85% of the morphologically-selected E/S0
galaxies at z=0 depending on their luminosity evolution. It is revealed that
more than half, but not all, of the present-day early-type galaxies had already
been formed into quiescent passive galaxies at z=1.Comment: 28 pages, accepted for publication in Astrophysical Journal. The full
version of the paper including Fig.3 and Fig.4 (large size) in full
resolution is put at
http://optik2.mtk.nao.ac.jp/~yamada/astronomy/sxdsred.htm
The Morphological Content of Ten EDisCS Clusters at 0.5 < z < 0.8
We describe Hubble Space Telescope (HST) imaging of 10 of the 20 ESO Distant
Cluster Survey (EDisCS) fields. Each ~40 square arcminute field was imaged in
the F814W filter with the Advanced Camera for Surveys Wide Field Camera. Based
on these data, we present visual morphological classifications for the ~920
sources per field that are brighter than I_auto=23 mag. We use these
classifications to quantify the morphological content of 10
intermediate-redshift (0.5 < z < 0.8) galaxy clusters within the HST survey
region. The EDisCS results, combined with previously published data from seven
higher redshift clusters, show no statistically significant evidence for
evolution in the mean fractions of elliptical, S0, and late-type (Sp+Irr)
galaxies in clusters over the redshift range 0.5 < z < 1.2. In contrast,
existing studies of lower redshift clusters have revealed a factor of ~2
increase in the typical S0 fraction between z=0.4 and z=0, accompanied by a
commensurate decrease in the Sp+Irr fraction and no evolution in the elliptical
fraction. The EDisCS clusters demonstrate that cluster morphological fractions
plateau beyond z ~ 0.4. They also exhibit a mild correlation between
morphological content and cluster velocity dispersion, highlighting the
importance of careful sample selection in evaluating evolution. We discuss
these findings in the context of a recently proposed scenario in which the
fractions of passive (E,S0) and star-forming (Sp,Irr) galaxies are determined
primarily by the growth history of clusters.Comment: 18 pages, 7 figures; To be published in ApJ; minor changes made to
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