A Deep Radio Survey of Abell 2125. III. The Cluster Core: Merging and Stripping

Abstract

We use radio, near-IR, optical, and X-ray observations to examinedynamic processes in the central region of the rich galaxy cluster Abell2125. In addition to the central triple of E and cD galaxies, includingmembers of both major dynamical subsystems identified from a redshiftsurvey, this region features a galaxy showing strong evidence forongoing gas stripping during a high-velocity passage through the gas inthe cluster core. The disk galaxy C153 exhibits a plume stretchingtoward the cluster center seen in soft X-rays by Chandra, parts of whichare also seen in [O II] emission and near-UV continuum light. HubbleSpace Telescope imaging shows a distorted disk with star-forming knotsasymmetrically distributed and remnant spiral structure possibly definedby dust lanes. The stars and ionized gas in this disk are kinematicallydecoupled, demonstrating that pressure stripping (possibly turbulent, aswell as ram) must be important, and that tidal disruption is not theonly mechanism at work. Comparison of the gas properties seen in theX-ray and optical data on the plume highlight significant and poorlyknown features of the history of stripped gas in the intracluster mediumthat could be clarified through further observations of this system. Thenucleus of C153 also hosts an active galactic nucleus, shown by the weakand distorted extended radio emission and a radio-compact core. Theunusual strength of the stripping signatures in this instance is likelyrelated to the very high relative velocity of the galaxy with respect tothe intracluster medium during a cluster-cluster merger and its passagevery near the core of the cluster. An additional sign of recentdynamical events is the diffuse starlight asymmetrically placed aboutthe central triple in a cD envelope. Transient and extreme dynamicalevents as seen in A2125 may be important drivers of galaxy evolution inthe cores of rich clusters.