85 research outputs found
A Deep Radio Survey of Abell 2125 II: Accelerated Galaxy Evolution during a Cluster-Cluster Merger
Using our extensive radio, optical, near-IR and X-ray imaging and
spectroscopy, we consider the reason for the unusually large number of radio
detected galaxies, mostly found outside the cluster core, in Abell 2125
(z=0.2465, richness class 4). With 20-cm VLA data, we detect continuum emission
from 90 cluster members. The multiwavelength properties of these galaxies
suggest that most of the radio emission is due to an enhanced star-formation
rate. The dynamical study of Miller et al (2004) suggests that Abell 2125 is
undergoing a major cluster-cluster merger, with our view within 30 degrees of
the merger axis and within 0.2 Gyr of core passage. The combination of
projection effects and the physical processes at work during this special time
in the cluster's evolution seem likely to be responsible for the unusual level
of activity we see in the cluster. We argue that tidal effects on individual
cluster members, often far from the cluster core, are responsible for the
increased star formation. Our results are consistent with the idea that disk
galaxies during this phase of a cluster's evolution undergo rapid evolution,
through a burst of star formation, on their way to becoming S0's.Comment: 53 pages, 12 figures, accepted AJ, paper with full resolution figures
is available at http:www.aoc.nrao.edu/~fowen/papers/a2125/a2125paper2.ps.g
A Deep Radio Survey of Abell 2125 III: The Cluster Core - Merging and Stripping
We use radio, near-IR, optical, and X-ray observations to examine dynamic
processes in the central region of Abell 2125. In addition to the central
triple, including members of both major dynamical subsystems identified from a
redshift survey, this region features a galaxy showing strong evidence for
ongoing gas stripping during a high-velocity passage through the gas in the
cluster core. The disk galaxy C153 exhibits a plume stretching toward the
cluster center seen in soft X-rays by Chandra, parts of which are also seen in
[O II] emission and near-UV continuum light. HST imaging shows a distorted
disk, with star-forming knots asymmetrically distributed and remnant spiral
structure possibly defined by dust lanes. The stars and ionized gas in its disk
are kinematically decoupled, demonstrating that pressure stripping must be
important, and that tidal disruption is not the only mechanism at work.
Comparison of the gas properties seen in the X-ray and optical data on the
plume highlight significant features of the history of stripped gas in the
intracluster medium. The nucleus of C153 also hosts an AGN, shown by the weak
and distorted extended radio emission and a radio compact core. The unusual
strength of the stripping signatures in this instance is likely related to the
high relative velocity of the galaxy with respect to the intracluster medium,
during a cluster/cluster merger, and its passage very near the core of the
cluster. Another sign of recent dynamical events is diffuse starlight
asymmetrically placed about the central triple in a cD envelope. Transient and
extreme dynamical events as seen in Abell 2125 may be important drivers of
galaxy evolution in the cores of rich clusters.Comment: 36 pages, 16 figures, accepted AJ, paper with full resolution figures
is available at http:www.aoc.nrao.edu/~fowen/papers/a2125/a2125paper3.ps.g
Gemini-South + FLAMINGOS Demonstration Science: Near-Infrared Spectroscopy of the z=5.77 Quasar SDSS J083643.85+005453.3
We report an infrared 1-1.8 micron (J+H-bands), low-resolution (R=450)
spectrogram of the highest-redshift radio-loud quasar currently known, SDSS
J083643.85+005453.3, obtained during the spectroscopic commissioning run of the
FLAMINGOS multi-object, near-infrared spectrograph at the 8m Gemini-South
Observatory. These data show broad emission from both CIV 1549 and CIII] 1909,
with strengths comparable to lower-redshift quasar composite spectra. The
implication is that there is substantial enrichment of the quasar environment,
even at times less than a billion years after the Big Bang. The redshift
derived from these features is z = 5.774 +/- 0.003, more accurate and slightly
lower than the z = 5.82 reported in the discovery paper based on the
partially-absorbed Lyman-alpha emission line. The infrared continuum is
significantly redder than lower-redshift quasar composites. Fitting the
spectrum from 1.0 to 1.7 microns with a power law f(nu) ~ nu^(-alpha), the
derived power law index is alpha = 1.55 compared to the average continuum
spectral index = 0.44 derived from the first SDSS composite quasar.
Assuming an SMC-like extinction curve, we infer a color excess of E(B-V) = 0.09
+/- 0.01 at the quasar redshift. Only approximately 6% of quasars in the
optically-selected Sloan Digital Sky Survey show comparable levels of dust
reddening.Comment: 10 pages, 1 figure; to appear in the Astrophysical Journal Letter
Redshifts and Optical Properties for a Statistically Complete Sample of Poor Galaxy Clusters
From the poor cluster catalog of White et al. (1996), we define a sample of
71 optically-selected poor galaxy clusters. The surface-density enhance- ment
we require for our clusters falls between that of the loose associations of
Turner and Gott (1976) and the Hickson compact groups (Hickson, 1982). We
review the selection biases and determine the statistical comleteness of the
sample. For this sample, we report new velocity measurements made with the ARC
3.5-m Dual-Imaging spectrograph and the 2.3-m Steward Observatory MX fiber
spectrograph. Combining our own measurements with those from the literature, we
examine the velocity distributions, velocity dispersions, and 1-d velocity
substructure for our poor cluster sample, and compare our results to other poor
cluster samples. We find that approximately half of the sample may have
significant 1-d velocity substructure. The optical morphology, large-scale
environment, and velocity field of many of these clusters is indicative of
young, dynamically evolving systems. In future papers, we will use this sample
to derive the poor cluster X-ray luminosity function and gas mass function (see
astro-ph/9606120), and will examine the optical/X-ray properties of the
clusters in more detail.Comment: 15 pages LaTeX, 3 tables, 5 postscript figures. To appear in the
August 1996 Astronomical Journa
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