Gas sloshing and cold fronts in pre-merging galaxy cluster Abell 98

TL;DR

This paper presents detailed Chandra X-ray observations of the complex pre-merger galaxy cluster Abell 98, revealing gas sloshing, cold fronts, shock features, and a cool core remnant, advancing understanding of cluster merger dynamics.

Contribution

It provides the first detailed analysis of gas sloshing and cold fronts in Abell 98, including temperature and density measurements across edges, and identifies a ram-pressure stripped cool core tail.

Findings

Detection of gas sloshing spirals in A98N and A98S.

Identification of cold front and shock front with Mach number ~1.5.

Discovery of a cooler tail indicating a ram-pressure stripped cool core.

Abstract

We present deep Chandra observations of the pre-merger galaxy cluster Abell 98. Abell 98 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 detection of gas sloshing spirals in A98N and in the eastern core of A98S. We detect 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. We measure the temperatures and gas densities across those edges, and find that the eastern edge appears to be a cold front while the western edge is a shock front with a Mach number of $\cal{M}$ $\approx$ 1.5. We detect 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-$\sigma$ level, suggesting the tail is part of a cool core remnant that has been ram-pressure stripped.