Suzaku Observations of the Merging Cluster Abell 85: Temperature Map and Impact Direction

Abstract

Abstract To investigate the present situation of the merging in the southern outer region of Abell 85, we carried out long-time ($\sim$ 100 ks) observations with Suzaku, and produced an X-ray hardness ratio map. We found a high hardness ratio peak on the east side of a subcluster located south of the cluster; an X-ray spectrum of the region including this peak indicates a high temperature of $\sim$ 8.5 keV. This hot spot has not been reported so far. We consider that this hot spot is a postshock region produced by the infall of the subcluster from the southwest. By using the Rankine–Hugoniot jump conditions for shocks, the Mach number and the infall velocity of the subcluster were obtained as 1.5$\ \pm\ $0.2 and 1950$^{+290}_{-280}\ $km s$^{-1}$, respectively, in the case of merging with the subcluster from the southwest direction. By using the difference in redshift between A 85 and the subcluster obtained from optical observations, the angle between the line of sight and the direction of the motion of the subcluster is estimated to be 75$^{\circ}$$^{+7^{\circ}}_{-8^\circ}$. We estimate the kinetic energy of the subcluster and the energy used for the intracluster medium (ICM) heating to be $\sim$ 10$^{63}$ and $\lesssim\ $8 $\times$ 10$^{60}\ $erg, respectively. This shows that the deceleration of the subcluster by the ICM heating has been negligibly small.