Suzaku observations of the merging cluster abell 85: Temperature map and impact direction

To investigate the present situation of the merging in the southern outer region of Abell 85, we carried out long time (∼ lOOks) 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 ∼ 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 ±0.2 and 1950_-280 ⁺²⁹⁰km 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°^+7°_-8°,. We estimate the kinetic energy of the subcluster and the energy used for the intracluster medium (ICM) heating to be ∼ 10⁶³ and ≲8 × l0⁶⁰erg, respectively. This shows that the deceleration of the subcluster by the ICM heating has been negligibly small.