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 dynamicprocesses in the central region of Abell 2125. In addition to the centraltriple, including members of both major dynamical subsystems identified from aredshift survey, this region features a galaxy showing strong evidence forongoing gas stripping during a high-velocity passage through the gas in thecluster core. The disk galaxy C153 exhibits a plume stretching toward thecluster 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 distorteddisk, with star-forming knots asymmetrically distributed and remnant spiralstructure possibly defined by dust lanes. The stars and ionized gas in its diskare kinematically decoupled, demonstrating that pressure stripping must beimportant, 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 theplume highlight significant features of the history of stripped gas in theintracluster medium. The nucleus of C153 also hosts an AGN, shown by the weakand distorted extended radio emission and a radio compact core. The unusualstrength of the stripping signatures in this instance is likely related to thehigh relative velocity of the galaxy with respect to the intracluster medium,during a cluster/cluster merger, and its passage very near the core of thecluster. Another sign of recent dynamical events is diffuse starlightasymmetrically placed about the central triple in a cD envelope. Transient andextreme dynamical events as seen in Abell 2125 may be important drivers ofgalaxy evolution in the cores of rich clusters.