A rare, strong shock front in the merging cluster SPT-CL J2031-4037

TL;DR

This study reports the discovery of a rare, strong shock front in a merging galaxy cluster, with detailed measurements of shock properties and implications for shock heating models, based on deep Chandra X-ray observations.

Contribution

First detailed analysis of a rare, high Mach number shock front in a merging galaxy cluster using deep X-ray data, confirming shock properties and testing heating models.

Findings

Detected two shock fronts with detailed temperature and density jumps.

Identified a rare high Mach number shock (M > 2) in a merging cluster.

Supported Coulomb collisional heating over instant heating models.

Abstract

We present our findings from the new deep Chandra observations ($256$ ks) of the merging galaxy cluster SPT-CL J2031-4037 at $z = 0.34$. Our observations reveal intricate structures seen in a major merger akin to the Bullet Cluster. The X-ray data confirm the existence of two shock fronts, one to the northwest and one to the southeast by directly measuring the temperature jump of gas across the surface brightness edges. The stronger shock front in the northwest has a density jump of $3.16 \pm 0.34$ across the sharp surface brightness edge and Mach number $M = 3.36^{+0.87}_{-0.48}$, which makes this cluster one of the rare merging systems with a Mach number $M > 2$. We use the northwestern shock to compare two models for shock heating - the instant heating model and the Coulomb collisional heating model, and we determine that the temperatures across the shock front agree with the Coulomb collisional model of heating. For the shock front in the southeastern region, we find a density jump of $1.53 \pm 0.14$ and a Mach number of $M = 1.36 ^{+0.09}_{-0.08}$.