Gas Sloshing and Cold Fronts in Pre-merging Galaxy Cluster A98

Abstract

We present deep Chandra observations of the pre-merger galaxy cluster Abell 98 (A98). A98 is a complex merging system. While the northern (A98N) and central subclusters (A98S) are merging along the north–south direction, A98S is undergoing a separate late-stage merger, with two distinct X-ray cores. We report the detection of a gas sloshing spiral and two cold front edges in A98N. We find two more surface brightness edges along the east direction of the eastern core and west direction of the western core of A98S. By measuring the gas temperatures and densities across those edges, we confirm that the eastern edge appears to be a cold front while the western edge is a shock front with a Mach number ${ \mathcal M }$ ≈ 1.5. We detect a spiral structure and a “tail” of X-ray emission associated with the eastern core of A98S. Our measurement indicates that the tail is cooler than the surrounding gas at a 4.2 σ level. This may suggest that the tail and the spiral structures are the results of ram-pressure stripping, as the eastern core orbits in the main cluster’s gravitational potential.

Keywords

• X-ray astronomy