# Chandra observation of a cold front in Abell 2554

## TL;DR

This paper reports Chandra X-ray observations of Abell 2554, revealing a cold front, substructure, and evidence of a past merger, indicating the cluster's dynamic disturbance and complex thermodynamics.

## Contribution

First detailed analysis of a cold front in Abell 2554 using Chandra data, identifying substructure and thermodynamic properties related to cluster mergers.

## Key findings

- Detection of a cold front at 60 kpc from the core.
- Identification of a northern substructure at z=0.1082.
- Evidence of a weak bow-shock with Mach number ~1.1.

## Abstract

We present the evidence for the existence of substructure in the cold front cluster A2554 based on a 20.14 ks Chandra observation. Using centroid shift and X-ray brightness concentration parameters, we confirm that A2554 is a dynamically disturbed system. We detect two dominant structures; a main cluster at z = 0.1108 and a foreground northern substructure at z = 0.1082. The analysis reveals an X-ray surface brightness edge at r \simeq 60 kpc from the cluster core. The thermodynamical profiles across the edge are ruling out the shock scenario. The temperature jump (from \sim 6 keV to \sim 10 keV), and pressure equilibrium (P0/P1 = 1.01 \pm 0.23) across the edge, are consistent with the definition of a cold front with a Mach number M=0.94^{+0.13}_{-0.17} also observed a weak bow-shock at \sim 100 kpc in front of the cold cloud, corresponding an upper limit to the Mach number M \sim 1.1. If the northern substructure was not related to the cold front, we conclude that the transonic motion of the cloud is caused by a merger, which was weak or occurred long ago.