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

TL;DR

This study uses Suzaku X-ray observations to map temperature variations in Abell 85, revealing a hot postshock region indicating a subcluster infall with specific velocity and angle, and assessing energy transfer during merging.

Contribution

First detailed temperature map of Abell 85's merging region using Suzaku, identifying a hot postshock spot and quantifying subcluster infall dynamics.

Findings

Identified a hot (~8.5 keV) postshock region in Abell 85.

Estimated subcluster infall velocity as ~1950 km/s.

Determined the infall angle to be approximately 75 degrees.

Abstract

To investigate the present situation of the merging in the southern outer region of Abell 85, we carried out long (~100 ks) observations with Suzaku, and produced an X-ray hardness ratio map. We found a high hardness ratio peak in the east side of a subcluster located in the 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 are obtained as 1.5 +/- 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 redshift difference between the 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} degrees. We estimate the kinetic energy of the subcluster and the energy used for intracluster medium (ICM) heating to be ~10^{63} and \lesssim 8 \times 10^{60} erg, respectively. This shows that the deceleration of the subcluster by ICM heating has been negligibly small.