SPT-CL J0205-5829: A z = 1.32 Evolved Massive Galaxy Cluster in the South Pole Telescope Sunyaev-Zel'dovich Effect Survey

TL;DR

This paper reports the discovery and detailed analysis of SPT-CL J0205-5829, the most massive galaxy cluster at z>1.2 identified via Sunyaev-Zel'dovich effect, with implications for galaxy evolution and cosmology.

Contribution

It presents the highest redshift, most massive SZ-selected galaxy cluster with multi-wavelength observations confirming its properties and rarity within the standard cosmological model.

Findings

The cluster has a mass of approximately 4.9×10^14 solar masses.

Brightest galaxies are already evolved with old stellar populations.

The cluster's existence aligns with expectations in a flat LambdaCDM universe.

Abstract

The galaxy cluster SPT-CL J0205-5829 currently has the highest spectroscopically-confirmed redshift, z=1.322, in the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. XMM-Newton observations measure a core-excluded temperature of Tx=8.7keV producing a mass estimate that is consistent with the Sunyaev-Zel'dovich derived mass. The combined SZ and X-ray mass estimate of M500=(4.9+/-0.8)e14 h_{70}^{-1} Msun makes it the most massive known SZ-selected galaxy cluster at z>1.2 and the second most massive at z>1. Using optical and infrared observations, we find that the brightest galaxies in SPT-CL J0205-5829 are already well evolved by the time the universe was <5 Gyr old, with stellar population ages >3 Gyr, and low rates of star formation (<0.5Msun/yr). We find that, despite the high redshift and mass, the existence of SPT-CL J0205-5829 is not surprising given a flat LambdaCDM cosmology with Gaussian initial perturbations. The a priori chance of finding a cluster of similar rarity (or rarer) in a survey the size of the 2500 deg^2 SPT-SZ survey is 69%.