566 research outputs found
M/L and Color Evolution for A Deep Sample of M* Cluster Galaxies at z~1: The Formation Epoch and the Tilt of the Fundamental Plane
We have measured velocity dispersions for a sample of 36 galaxies with J <
21.2 or Mr < -20.6 mag in MS1054-03, a massive cluster of galaxies at z = 0.83.
Our data are of uniformly high quality down to our selection limit, our 16-hour
exposures typically yielding errors of only \delta(dispersion)~10% for L* and
fainter galaxies. By combining our measurements with data from the literature,
we have 53 cluster galaxies with measured dispersions, and HST/ACS-derived
sizes, colors and surface brightnesses. This sample is complete for the typical
L* galaxy at z~1, unlike most previous z~1 cluster samples which are complete
only for the massive cluster members (>1e11 M_sun). We find no evidence for a
change in the tilt of the fundamental plane (FP). Nor do we find evidence for
evolution in the slope of the color-dispersion relation and M/L_B-dispersion
relations; measuring evolution at a fixed dispersion should minimize the impact
of size evolution found in other work. The M/L_B at fixed dispersion evolves by
\Delta log10 M/L_B=-0.50 +/- 0.03 between z=0.83 and z=0.02 or d(log10
M/L_B)=-0.60 +/- 0.04 dz, and we find \Delta (U-V)_z=-0.24 +/- 0.02 mag at
fixed dispersion in the rest-frame, matching the expected evolution in M/L_B
within 2.25 standard deviations. The implied formation redshift from both the
color and M/L_B evolution is z*=2.0 +/- 0.2 +/- 0.3 (sys), during the epoch in
which the cosmic star-formation activity peaked, with the systematic
uncertainty showing the dependence of z* on the assumptions we make about the
stellar populations. The lack of evolution in either the tilt of the FP or in
the M/L- and color-dispersion relations imply that the formation epoch depends
weakly on mass, ranging from z*=2.3 +1.3 -0.3 at 300 km/s to z*=1.7 +0.3 -0.2
at 160 km/s and implies that the IMF similarly varies slowly with galaxy mass.Comment: revised; typos corrected, references updated, and other cosmetic
changes to meet ApJ format ApJ accepted, 22 pages in emulate ApJ format, 8
color figures, 1 b/w figur
Infall, the Butcher-Oemler Effect, and the Descendants of Blue Cluster Galaxies at z~0.6
Using wide-field HST/WFPC2 imaging and extensive Keck/LRIS spectroscopy, we
present a detailed study of the galaxy populations in MS2053--04, a massive,
X-ray luminous cluster at z=0.5866. Analysis of 149 confirmed cluster members
shows that MS2053 is composed of two structures that are gravitationally bound
to each other; their respective velocity dispersions are 865 km/s (113 members)
and 282 km/s (36 members). MS2053's total dynamical mass is 1.2x10^15 Msun.
MS2053 is a classic Butcher-Oemler cluster with a high fraction of blue members
(24%) and an even higher fraction of star-forming members (44%), as determined
from their [OII] emission. The number fraction of blue/star-forming galaxies is
much higher in the infalling structure than in the main cluster. This result is
the most direct evidence to date that the Butcher-Oemler effect is linked to
galaxy infall. In terms of their colors, luminosities, estimated internal
velocity dispersions, and [OII] equivalent widths, the infalling galaxies are
indistinguishable from the field population. MS2053's deficit of S0 galaxies
combined with its overabundance of blue spirals implies that many of these
late-types will evolve into S0 members. The properties of the blue cluster
members in both the main cluster and infalling structure indicate they will
evolve into low mass, L<L* galaxies with extended star formation histories like
that of low mass S0's in Coma. Our observations show that most of MS2053's blue
cluster members, and ultimately most of its low mass S0's, originate in the
field. Finally, we measure the redshift of the giant arc in MS2053 to be
z=3.1462; this object is one in only a small set of known strongly lensed
galaxies at z>3.Comment: Accepted by ApJ. Version with full resolution figures available at
http://www.exp-astro.phys.ethz.ch/tran/outgoing/ms2053.ps.g
A High Merger Fraction in the Rich Cluster MS1054-03 at z=0.83: Direct Evidence for Hierarchical Formation of Massive Galaxies
We present a morphological study of the galaxy population of the luminous
X-ray cluster MS1054-03 at z=0.83. The sample consists of 81 spectroscopically
confirmed cluster members in a 3 x 2 Mpc area imaged in F606W and F814W with
WFPC2. We find thirteen ongoing mergers in MS1054-03, comprising 17% of the L >
L* cluster population. Most of these mergers will likely evolve into luminous
(\sim 2 L*) elliptical galaxies, and some may evolve into S0 galaxies. Assuming
the galaxy population in MS1054-03 is typical for its redshift it is estimated
that \sim 50% of present-day cluster ellipticals experienced a major merger at
z < 1. The mergers are preferentially found in the outskirts of the cluster,
and probably occur in small infalling clumps. Morphologies, spectra, and colors
of the mergers show that their progenitors were typically E/S0s or early-type
spirals with mean stellar formation redshifts z* \gtrsim 1.7. The red colors of
the merger remnants are consistent with the low scatter in the color-magnitude
relation in rich clusters at lower redshift. The discovery of a high fraction
of mergers in this young cluster is direct evidence against formation of
ellipticals in a single ``monolithic'' collapse at high redshift, and in
qualitative agreement with predictions of hierarchical models for structure
formation.Comment: Added GIF version of Figure 1. At
http://www.astro.rug.nl/~dokkum/preprints/merger_fig1.eps.gz the PS file is
available. Accepted for publication in ApJ Letter
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