SPT-CL J0417-4748: A Deep Chandra Study of a Relaxed Galaxy Cluster Without Central Star Formation

TL;DR

This study provides a detailed Chandra X-ray analysis of a relaxed galaxy cluster at z=0.58, revealing a cool-core system with no current star formation or strong AGN activity, highlighting the quenching processes in such environments.

Contribution

It presents the first detailed X-ray and multiwavelength analysis of SPT J0417, demonstrating a relaxed cool-core cluster with quenched star formation and minimal AGN activity, offering insights into thermal regulation.

Findings

The cluster has a typical cool-core density and entropy profile.

No evidence of recent star formation or strong AGN activity in the BCG.

Cooling and star formation are effectively quenched in this relaxed cluster.

Abstract

We present an in-depth Chandra X-ray analysis of the galaxy cluster SPT-CL J0417$-$4748 (hereafter SPT J0417), at z = 0.58, with a focus on its thermodynamic properties and the apparent absence of central star formation. Utilizing a total Chandra exposure of 103 ks, we find that the large-scale X-ray morphology is consistent with a dynamically relaxed, cool-core system. The intracluster medium (ICM) shows a central density of 0.08+/-0.01 cm^{-3}, a central pseudo-entropy of 26^{+6}_{-5} keVcm^{2} and a central cooling time of 515^{+96}_{-75} Myr, values typical of massive cool-core clusters. Despite these conditions, no evidence of recent or ongoing star formation is detected in the brightest cluster galaxy (BCG). Spectral energy distribution (SED) fitting of DES photometry indicates that the bulk of the stellar population formed at z~1.25, with no significant star formation over the past ~3 Gyr, while optical spectra from Magellan show no [O II] emission. Complementary ASKAP radio and Spitzer infrared data indicate a lack of strong current AGN activity in the BCG. SPT J0417 exemplifies massive, relaxed, cool-core clusters in which cooling and star formation appear almost completely quenched, providing valuable insights into how AGN feedback regulates the long-term thermal balance of the intracluster medium.