A. Rettura$^{3}$, M. Brodwin$^{4}$, A. Galametz$^{5}$, D. Wylezalek$^{6}$, C. Bridge$^{2,7}$, C. J. Conselice$^{1}$, C. De Breuck$^{8}$, A. H. Gonzalez$^{9}$, M. Jarvis$^{10,11}$'
bibliography:
- 'protoclustersbib.bib'
title: 'A mature galaxy cluster at $z=1.58$ around the radio galaxy 7C1753$+$6311'
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Introduction
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To understand the formation history of galaxies in the densest environments, clusters, it is important to study their progenitors: high-redshift protocluster galaxies. Several techniques are now employed to locate clusters and protoclusters at $z>1$, such as large photometric surveys [e.g. @Chiang2014; @Stanford2014], surveys exploiting the Sunyaev Zel’dovich (SZ) effect [e.g. @Hasselfield2013; @Bleem2015; @Planck2015], and X-ray detections of the intracluster medium (ICM) [e.g. @Willis2013]. Unfortunately, many of these methods are expensive, requiring deep coverage of large fields-of-view in order to locate the rare overdensities. Massive clusters have been found with the SZ effect out to $z\sim1.5$, with a few candidates at even higher redshifts [e.g. @Tozzi2015 see also [@Brodwin2012]]. These, however, are rare systems; SZ and X-ray surveys struggle to find the more typical, lower mass clusters at $z>1.5$ since the signal from these methods scales with cluster mass. The high-redshift progenitors of the majority of local $M \sim 10^{14}$ clusters will be missed since they lack sufficiently massive cluster cores at 