The growth of the galaxy cluster Abell 85: mergers, shocks, stripping and seeding of clumping

Abstract

We present the results of deep Chandra, XMM-Newton and Suzaku observations of the nearby galaxy cluster Abell 85, which is currently undergoing at least two mergers, and in addition shows evidence for gas sloshing which extends out to r ~ 600 kpc. One of the two infalling subclusters, to the south of the main cluster center, has a dense, X-ray bright cool core and a tail extending to the southeast. The northern edge of this tail is strikingly smooth and sharp (narrower than the Coulomb mean free path of the ambient gas) over a length of 200 kpc, while toward the southwest the boundary of the tail is blurred and bent, indicating a difference in the plasma transport properties between these two edges. The thermodynamic structure of the tail strongly supports an overall northwestward motion. We propose, that a sloshing-induced tangential, ambient, coherent gas flow is bending the tail eastward. The brightest galaxy of this subcluster is at the leading edge of the dense core, and is trailed by the tail of stripped gas, suggesting that the cool core of the subcluster has been almost completely destroyed by the time it reached its current radius of r ~ 500 kpc. The surface-brightness excess, likely associated with gas stripped from the infalling southern subcluster, extends toward the southeast out to at least r_500 of the main cluster, indicating that the stripping of infalling subclusters may seed gas inhomogeneities. The second merging subcluster appears to be a diffuse non-cool core system. Its merger is likely supersonic with a Mach number of ~ 1.4.