High-Redshift Cool-Core Galaxy Clusters Detected via the Sunyaev--Zel'dovich Effect in the South Pole Telescope Survey

TL;DR

This study investigates the properties of cool-core galaxy clusters selected via the Sunyaev--Zel'dovich effect, revealing the presence of strong cool cores at high redshifts and comparing their characteristics with X-ray-selected samples.

Contribution

First analysis of cool-core properties in SZ-selected galaxy clusters at high redshift, demonstrating the existence of strong cool cores beyond z > 0.5 and comparing selection methods.

Findings

Detection of several new z > 0.5 cool-core clusters, including two strong cool cores.

High-z cool-core fraction estimated between 7% and 56%.

Cool-core strength correlates inversely with BCG-X-ray centroid offset.

Abstract

We report the first investigation of cool-core properties of galaxy clusters selected via their Sunyaev--Zel'dovich (SZ) effect. We use 13 galaxy clusters uniformly selected from 178 deg^2 observed with the South Pole Telescope (SPT) and followed up by the Chandra X-ray Observatory. They form an approximately mass-limited sample (> 3 x 10^14 M_sun h^-1_70) spanning redshifts 0.3 < z < 1.1. Using previously published X-ray-selected cluster samples, we compare two proxies of cool-core strength: surface brightness concentration (cSB) and cuspiness ({\alpha}). We find that cSB is better constrained. We measure cSB for the SPT sample and find several new z > 0.5 cool-core clusters, including two strong cool cores. This rules out the hypothesis that there are no z > 0.5 clusters that qualify as strong cool cores at the 5.4{\sigma} level. The fraction of strong cool-core clusters in the SPT sample in this redshift regime is between 7% and 56% (95% confidence). Although the SPT selection function is significantly different from the X-ray samples, the high-z cSB distribution for the SPT sample is statistically consistent with that of X-ray-selected samples at both low and high redshifts. The cool-core strength is inversely correlated with the offset between the brightest cluster galaxy and the X-ray centroid, providing evidence that the dynamical state affects the cool-core strength of the cluster. Larger SZ-selected samples will be crucial in understanding the evolution of cluster cool cores over cosmic time.