Reconstructing the Merger History of the A3266 Galaxy Cluster

Abstract

A temperature map of the A3266 galaxy cluster has been derived from the ASCA GIS observations. It shows an asymmetric pattern of heating indicative of an ongoing merger between a group sized sub-cluster and the main cluster. The galaxy distribution shows two peaks connected in a barlike structure running NE to SW through the central region of the main cluster, defining the merger axis. The temperature of the intergalactic medium generally decreases from SW to NE along the merger axis with a peak of 13.2 +3.4/-2.0 keV in a region which is perpendicular to the merger axis and extends through the main cluster density peak. The central bar has a velocity dispersion of ~1300 km/s, compared to \~1000 km/s for the surrounding cluster. The central bar also has two distinct density peaks in the distribution of galaxies, yet it has a velocity distribution which is consistent with a single Gaussian. This implies a merger in the plane of the sky. The optical and X-ray data taken together show that a loose group of about ~30 galaxies has penetrated the main cluster from the SW, decoupling from their original intergroup medium and passing through a strong shock front. Two radio galaxies, one a wide angle tail morphology (WAT) and the other a narrow angle tail (NAT), are located to the SW of the main cluster in the post-shock gas. Since the merger is in the plane of the sky, a dynamical analysis cannot be applied to derive the velocity of the merger. Alternatively, using the pre- and post-shock gastemperature and assuming an adiabatic shock, we calculate a relative gas velocity of ~1400 km/s. The alignment of the NAT and WAT relative to the shock front combined with the high gas velocity from the merger implies that the observed radio morphologies formed via ram-pressure as a result of the merger.