The SRG/eROSITA All-Sky Survey: A comprehensive X-ray analysis of the Hydra I galaxy cluster

TL;DR

This paper presents a detailed X-ray and multiwavelength analysis of the Hydra I galaxy cluster using eROSITA, Chandra, and other data, revealing ICM properties, shocks, and accretion features extending to the cluster outskirts.

Contribution

It provides the first comprehensive characterization of Hydra I's ICM out to $3R_{200}$, including shock detection and correlation with non-thermal emissions and galaxy distribution.

Findings

Detection of two weak ICM shocks near NGC 3311 with Mach number ~1.5

Identification of soft X-ray excesses correlated with galaxy distribution beyond $R_{200}$

ICM temperature and metallicity estimates consistent with simulations

Abstract

The Hydra I galaxy cluster (Abell 1060) is a nearby example of a low-temperature cluster that exhibits intermediate cool core and non-cool core properties. We aim to extend the characterization of the intracluster medium (ICM) properties at least until $R_{200}$ and study the correlation between the X-ray emission and non-thermal emission within $R=0.15$$R_{500}$, and optical/IR galaxy distribution beyond $R_{200}$. We used data from the first four SRG/eROSITA All-Sky Surveys and an archival Chandra observation to image the X-ray emission from Abell 1060. We also used multiwavelength data from TGSS (radio), 2MASS (IR), and NED (optical) to investigate the non-thermal emission, 2D galaxy distribution, and its redshift evolution, respectively. The surface brightness and spectral analyses are also extended until 3$R_{200}$ and $R_{200}$, respectively, following a detailed cosmic X-ray background (CXB) analysis. Our fully corrected eROSITA image showcases a relaxed ICM morphology within $R_{500}$. We detect two weak ICM shocks with Mach number $M\approx 1.5$ near the central galaxy NGC 3311 that coincide with diffuse radio emission along the line of sight. Furthermore, we detect multiple soft X-ray excesses with high spatial correlation with the 2D optical galaxy distribution beyond $R_{200}$. In particular, the excess in the north has a significance of $5.8\sigma$ above the local CXB level. This suggests that Abell 1060's outskirts are actively accreting baryons. We also estimate the average ICM temperature and metallicity of $\langle k_\mathrm{B}T \rangle=2.27\substack{+0.15\\-0.11}\thinspace$ keV and $\langle Z\rangle=0.19\substack{+0.05\\-0.03}\thinspace Z_\odot$, respectively, from the 0.2-0.5$R_{500}$ annulus. Overall, the temperature profile is broadly consistent with the average temperature profiles from hydrodynamical simulation and Suzaku between 0.28$R_{200}$ and $R_{200}$.