paper

The Merger Dynamics of the Galaxy Cluster Abell 1775: New Insights from Chandra and XMM-Newton for a Cluster Simultaneously Hosting a WAT and a NAT Radio Sources

arXiv:2103.03382 · doi:10.3847/1538-4357/abf09e

Abstract

We present a new study of the merger dynamics of Abell~1775 by analyzing the high-quality Chandra and XMM-Newton archival data. We confirm/identify an arc-shaped edge (i.e., the head) at ~kpc west of the X-ray peak, a split cold gas tail that extends eastward to ~kpc, and a plume of spiral-like X-ray excess (within about ~kpc northeast of the cluster core) that connects to the end of the tail. The head, across which the projected gas temperature rises outward from ~keV to ~keV, is found to be a cold front with a Mach number of . Along the surfaces of the cold front and tail, typical KHI features (noses and wings, etc.) are found and are used to constrain the upper limit of the magnetic field (G) and the viscosity suppression factor (). Combining optical and radio evidence we propose a two-body merger (instead of systematic motion in a large-scale gas environment) scenario and have carried out idealized hydrodynamic simulations to verify it. We find that the observed X-ray emission and temperature distributions can be best reproduced with a merger mass ratio of 5 after the first pericentric passage. The NAT radio galaxy is thus more likely to be a single galaxy falling into the cluster center at a relative velocity of 2800~, a speed constrained by its radio morphology. The infalling subcluster is expected to have a relatively low gas content, because only a gas-poor subcluster can cause central-only disturbances as observed in such an off-axis merger.

arXiv comment12 figures, 5 tables, accepted for publication in the ApJ

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