The High-Redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Radio Source Properties

TL;DR

This study uses radio, optical, and infrared data to analyze high-redshift galaxy clusters with bent radio AGN, revealing how cluster environment influences radio morphology and galaxy evolution at z=0.35-2.2.

Contribution

It provides new insights into the relationship between radio source morphology and cluster environment at high redshift, including the roles of BCGs and galaxy infall/outflow dynamics.

Findings

Narrower radio opening angles correlate with richer clusters.

Over half of radio hosts are brightest cluster galaxies (BCGs).

A significant fraction of sources are outgoing or infalling, indicating complex cluster dynamics.

Abstract

The shape of bent, double-lobed radio sources requires a dense gaseous medium. Bent sources can therefore be used to identify galaxy clusters and characterize their evolutionary history. By combining radio observations from the Very Large Array Faint Images of the Radio Sky at Twenty centimeters (VLA FIRST) survey with optical and infrared imaging of 36 red sequence selected cluster candidates from the high-z Clusters Occupied by Bent Radio AGN (COBRA) survey (0.35 < z < 2.2), we find that radio sources with narrower opening angles reside in richer clusters, indicating that the cluster environment impacts radio morphology. Within these clusters, we determine 55.5% of our radio host galaxies are brightest cluster galaxies (BCGs) and that the remainder are associated with other luminous galaxies. The projected separations between the radio sources and cluster centers and the sizes of the opening angles of bent sources follow similar distributions for BCG and non-BCG host populations, suggesting that COBRA host galaxies are either BCGs or galaxies that may evolve into BCGs. By measuring the orientation of the radio sources relative to the cluster centers, we find between 30% and 42% of COBRA bent sources are outgoing and have passed through the cluster center, while between 8% and 58% of COBRA bent sources are infalling. Although these sources typically do not follow directly radial paths, the large population of outgoing sources contrasts what is observed in low-z samples of bent sources and may indicate that the intracluster medium is less dense in these high-z clusters.