X - ray Properties of the Abell 644 Cluster of Galaxies

We use new ASCA observations and archival ROSAT Position Sensitive Proportional Counter (PSPC) data to determine the X-ray spectral properties of the intracluster gas in Abell 644. From the overall spectrum, we determine the average gas temperature to be 8.64 −0.56 keV, and an abundance of 0.32 ± 0.04 Z⊙. The global ASCA and ROSAT spectra imply a cooling rate of 214 −91 M⊙ yr −1. The PSPC X-ray surface brightness profile and the ASCA data suggest a somewhat higher cooling rate. We determine the gravitational mass and gas mass as a function of radius. The total gravitating mass within 1.2 Mpc is 6.2 × 1014 M⊙, of which 20% is in the form of hot gas. There is a region of elevated temperature 1.5-5 to the west of the cluster center. The south-southwest region of the cluster also shows excess emission in the ROSAT PSPC X-ray image, aligned with the major axis of the optical cD galaxy in the center of the cluster. We argue that the cluster is undergoing or has recently undergone a minor merger. The combination of a fairly strong cooling flow and evidence for a merger make this cluster an interesting case to test the disruption of cooling flow in mergers. Subject headings: cooling flows — dark matter — galaxies: clusters: general — galaxies: clusters: individual (Abell 644) — intergalactic medium — X-rays: galaxies