A Large Population of High Redshift Galaxy Clusters in the IRAC Shallow Cluster Survey

TL;DR

This paper reports the discovery of 335 galaxy cluster candidates up to redshift 2 using IRAC data, confirming several at high redshift, analyzing their properties, and measuring their clustering to understand galaxy evolution and cosmology.

Contribution

It presents a new large sample of high-redshift galaxy clusters identified via a wavelet algorithm, with spectroscopic confirmation and analysis of their evolution and clustering.

Findings

12 clusters confirmed at z>1

Cluster autocorrelation function unchanged up to z=1.5

Average cluster mass approximately 10^14 solar masses

Abstract

We have identified 335 galaxy cluster and group candidates spanning 0<z<2, using a 4.5um selected sample of galaxies in a 7.25 deg^2 region in the Spitzer/IRAC Shallow Survey. Using full redshift probability distributions for all galaxies, clusters were identified as 3-dimensional overdensities using a wavelet algorithm. To date 12 clusters at z>1, and over 60 at z < 0.5 have been spectroscopically confirmed. The mean I-[3.6] color for cluster galaxies up to z~1 is well matched by a z_f=3 passively evolving model. At z>1, a wider range of formation histories is needed, but higher formation redshifts (i.e. z_f \ge 4-5) are favored for most clusters. The cluster autocorrelation function, measured for the first time out to z=1.5, is found not to have evolved over the last 10 Gyr, in agreement with the prediction from LCDM. The average mass of the IRAC Shallow Cluster Survey sample, inferred from its clustering, is ~ 10^14 Msun.