The High-Redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: The \spitzer Catalog

TL;DR

This study identifies 190 high-redshift galaxy cluster candidates around bent radio AGN using Spitzer/IRAC imaging, revealing a significant number of potential distant clusters and galaxy groups, with many associated with quasars.

Contribution

First large-scale infrared survey of high-redshift cluster candidates around bent radio AGN, expanding the known catalog of distant galaxy clusters and groups.

Findings

190 galaxy cluster candidates identified at high redshift

82% of fields show positive galaxy overdensity

many candidates are associated with quasars at z~1 to 3

Abstract

We present 190 galaxy cluster candidates (most at high redshift) based on galaxy overdensity measurements in the \spitzer/IRAC imaging of the fields surrounding 646 bent, double-lobed radio sources drawn from the Clusters Occupied by Bent Radio AGN (COBRA) Survey. The COBRA sources were chosen as objects in the VLA FIRST survey that lack optical counterparts in the Sloan Digital Sky Survey (SDSS) to a limit of $m_r=22$, making them likely to lie at high redshift. This is confirmed by our observations: the redshift distribution of COBRA sources with estimated redshifts peaks near $z=1$, and extends out to $z\approx3$. Cluster candidates were identified by comparing our target fields to a background field and searching for statistically significant ($\ge2\sigma$) excesses in the galaxy number counts surrounding the radio sources; 190 fields satisfy the $\ge2\sigma$ limit. We find that 530 fields (82.0\%) have a net positive excess of galaxies surrounding the radio source. Many of the fields with positive excesses but below the $2\sigma$ cutoff are likely to be galaxy groups. Forty-one COBRA sources are quasars with known spectroscopic redshifts, which may be tracers of some of the most distant clusters known.