169 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
The Dynamics of Abell 2125
We present 371 galaxy velocities in the field of the very rich cluster Abell
2125 (z~0.25). These were determined using optical spectroscopy collected over
several years from both the WIYN 3.5m telescope and NOAO Mayall 4m telescope.
Prior studies at a variety of wavelengths (radio, optical, and X-ray) have
indicated that A2125 is a likely cluster-cluster merger, a scenario which we
are able to test using our large velocity database. We identified 224 cluster
galaxies, which were subjected to a broad range of statistical tests using both
positional and velocity information to evaluate the cluster dynamics and
substructure. The tests confirmed the presence of substructures within the
Abell 2125 system at high significance, demonstrating that A2125 is a complex
dynamical system. Comparison of the test results with existing simulations
strengthens the merger hypothesis, and provides clues about the merger geometry
and stage. The merger model for the system can reconcile A2125's low X-ray
temperature and luminosity with its apparently high richness, and might also
explain A2125's high fraction of active galaxies identified in prior radio and
optical studies.Comment: 34 pages, including tables and 3 color figures; to appear in Ap
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