http://arxiv.org/abs/1808.02885
Shock waves provide a way to understand the merger configuration of galaxy clusters from X-ray data, e.g. constraining velocities of merging subclusters, even if the energy resolution of an instrument is not sufficient to measure the gas velocities directly via the Doppler effect. One of the pure geometrical proxies to the shock Mach number is the standoff distance, i.e. the distance between the leading edge of the shock and the contact discontinuity. In this work, we systematically investigate various effects that influence the estimates of the shock Mach number for a minor merger. These effects include (1) the gravitational potential well of the main cluster (causing acceleration/deceleration of the infalling subcluster), (2) the density and pressure gradients of the atmosphere in the main cluster, (3) the non-spherical shape of the subcluster, and (4) projection effects. The bias in the derived Mach number caused by the first two effects has opposite signs for the pre- and post-merger stages. Particularly, in the post-merger stage, the shock could be much farther away from the subcluster than predicted by a model of a rigid sphere moving at a constant speed in a uniform medium. This implies that a combination of the standoff distance with measurements of the Mach number from density/temperature jumps can differentiate between the pre- and post-merger stages, at least when the merger axis is close to the plane of sky or if the merger axis angle to the line of sight can be inferred.
C. Zhang, E. Churazov, W. Forman, et. al.
Fri, 10 Aug 18
29/45
Comments: 11 pages, 12 figures, submitted to MNRAS
You must be logged in to post a comment.