The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: The Spitzer Catalog

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 ≈ 3. Cluster candidates were identified by comparing our target fields to a background field and searching for statistically significant (≥ 2σ) excesses in the galaxy number counts surrounding the radio sources; 190 fields satisfy the ≥ 2σ 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 2σ 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.

The Massive and Distant Clusters of WISE Survey. VII. The Environments and Properties of Radio Galaxies in Clusters at z ∼ 1

“…As a last example, the relative motion of the AGN host galaxy with respect to the ICM can distort AGN outflows (e.g. bent-tail radio sources in galaxy clusters as seen in Paterno-Mahler et al 2017).…”

The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Follow-up Optical Imaging

“…Instead of searching for galaxy populations across large survey fields, AGN targeting can also be used to find clusters across a wide range of redshifts with a broad range of masses (e.g., Galametz et al 2012;Wylezalek et al 2013;Cooke et al 2015;Paterno-Mahler et al 2017). The Clusters Around Radio-Loud AGN (CARLA) survey find that radio-loud AGN (RLAGN) at 1.3 < z < 3.2 preferentially live in environments with positive excesses of galaxy counts above an average background in ∼ 92% of their sample and in denser, 2σ environments, such as clusters or groups, 55.3% of the time (e.g., Wylezalek et al 2013Wylezalek et al , 2014.…”

“…The first results of the high-z COBRA survey are presented in Blanton et al (2015) and Paterno-Mahler et al (2017). Of the 653 sources in the original sample, 646 were successfully observed with Spitzer in 3.6 µm with the Infrared Array Camera (IRAC; Fazio et al 2004).…”

“…Overall, 530 of the total 646 sources (≈ 82%) are in regions that have a higher density of sources than the mean of the SpUDs field. Paterno-Mahler et al (2017) additionally directly compare the COBRA selection methodology to that of the CARLA sample of RLAGN (Wylezalek et al 2013). In doing a direct comparison, Paterno-Mahler et al (2017) find that COBRA and CARLA identify regions with a similar overdensity, although CARLA identifies a higher percentage of rich clusters.…”

RELICS: A Strong Lens Model for SPT-CLJ0615–5746, a z = 0.972 Cluster

“…While there are quite a few known strong lensing clusters at lower redshifts, there are only a handful at z>0.8, despite the many targeted searches for high-redshift clusters (Wylezalek et al 2014;Bleem et al 2015;Paterno-Mahler et al 2017). For many of these high-redshift strong lensing clusters, strongly lensed galaxies are observed in the form of stretched arcs; however, no detailed lens models exist in the literature (Huang et al 2009;Gonzalez et al 2012).…”