Candidate Clusters of Galaxies at z > 1.3 Identified in the Spitzer South Pole Telescope Deep Field Survey

Abstract

We present 279 galaxy cluster candidates at z > 1.3 selected from the 94 deg^2 Spitzer South Pole Telescope Deep Field (SSDF) survey. We use a simple algorithm to select candidate high-redshift clusters of galaxies based on Spitzer/IRAC mid-infrared data combined with shallow all-sky optical data. We identify distant cluster candidates adopting an overdensity threshold that results in a high purity (80%) cluster sample based on tests in the Spitzer Deep, Wide-Field Survey of the Boötes field. Our simple algorithm detects all three 1.4 < z ≤ 1.75 X-ray detected clusters in the Boötes field. The uniqueness of the SSDF survey resides not just in its area, one of the largest contiguous extragalactic fields observed with Spitzer, but also in its deep, multi-wavelength coverage by the South Pole Telescope (SPT), Herschel/SPIRE, and XMM-Newton. This rich data set will allow direct or stacked measurements of Sunyaev-Zel'dovich effect decrements or X-ray masses for many of the SSDF clusters presented here, and enable a systematic study of the most distant clusters on an unprecedented scale. We measure the angular correlation function of our sample and find that these candidates show strong clustering. Employing the COSMOS/UltraVista photometric catalog in order to infer the redshift distribution of our cluster selection, we find that these clusters have a comoving number density N_c = (0.7^(+6.3)_(0.6)) x 10^(-7) h^3 Mpc^(-3) and a spatial clustering correlation scale length r_ 0 = (32 ± 7) h^(–1) Mpc. Assuming our sample is comprised of dark matter halos above a characteristic minimum mass, M _(min), we derive that at z = 1.5 these clusters reside in halos larger than M_(min) = 1.5^(+0.9)_(0.7) x 10^(14) h^(-1) M_⊙. We find that the mean mass of our cluster sample is equal to M_(mean) = 1.9^(+1.0)_(0.8) x 10^(14) h^(-1) M_⊙ ; thus, our sample contains the progenitors of present-day massive galaxy clusters.

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