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 the rich galaxy cluster Abell 2125. In addition to the central triple of E and cD galaxies, 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. Hubble Space Telescope 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 this disk are kinematically decoupled, demonstrating that pressure stripping (possibly turbulent, as well as ram) 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 and poorly known features of the history of stripped gas in the intracluster medium that could be clarified through further observations of this system. The nucleus of C153 also hosts an active galactic nucleus, 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 very 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. An additional sign of recent dynamical events is the diffuse starlight asymmetrically placed about the central triple in a cD envelope. Transient and extreme dynamical events as seen in A2125 may be important drivers of galaxy evolution in the cores of rich clusters.