Radio Galaxy Zoo: The Distortion of Radio Galaxies by Galaxy Clusters

Abstract

We study the impact of cluster environment on the morphology of a sample of 4304 extended radio galaxies from Radio Galaxy Zoo. A total of 87% of the sample lies within a projected 15 Mpc of an optically identified cluster. Brightest cluster galaxies (BCGs) are more likely than other cluster members to be radio sources, and are also moderately bent. The surface density as a function of separation from cluster center of non-BCG radio galaxies follows a power law with index 1.10 ± 0.03 out to 10 r 500 (∼ 7 Mpc), which is steeper than the corresponding distribution for optically selected galaxies. Non-BCG radio galaxies are statistically more bent the closer they are to the cluster center. Within the inner 1.5 r 500 (∼ 1 Mpc) of a cluster, non-BCG radio galaxies are statistically more bent in high-mass clusters than in low-mass clusters. Together, we find that non-BCG sources are statistically more bent in environments that exert greater ram pressure. We use the orientation of bent radio galaxies as an indicator of galaxy orbits and find that they are preferentially in radial orbits. Away from clusters, there is a large population of bent radio galaxies, limiting their use as cluster locators; however, they are still located within statistically overdense regions. We investigate the asymmetry in the tail length of sources that have their tails aligned along the radius vector from the cluster center, and find that the length of the inward-pointing tail is weakly suppressed for sources close to the center of the cluster.

The Abell 3391/95 galaxy cluster system

“…The projected distances are lower limits to the 3D distances; that is, the interaction processes shed light on the gas properties well beyond r 200 . This is consistent with statistical analyses of radio galaxy morphologies (e.g., Garon et al 2019). We also note the interesting faint extended radio source to the west of A3395s (S2/S3).…”

Simulated Interactions between Radio Galaxies and Cluster Shocks. II. Jet Axes Orthogonal to Shock Normals

“…Radio galaxies (RGs) are found from the cores to the extremities of galaxy clusters (e.g., Kale et al 2015;Padovani 2016;Garon et al 2019). Cluster RGs frequently appear significantly distorted from simple, bilateral, axial symmetry (e.g., Terni de Gregory et al 2017;Garon et al 2019), revealing non-axisymmetric environmental impacts. Sometimes the distortions can be attributed to galaxy motions relative to the cluster center.…”

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

“…More recently, radio loud AGNs have been used to trace both low-and high-z clusters and protoclusters (e.g. Blanton et al 2003;Galametz et al 2012;Wylezalek et al 2013Wylezalek et al , 2014Castignani et al 2014;Rigby et al 2014;Blanton et al 2015;Cooke et al 2015Cooke et al , 2016Noirot et al 2016;Paterno-Mahler et al 2017;Shen et al 2017;Noirot et al 2018;Shimakawa et al 2018;Croston et al 2019;Garon et al 2019;Moravec et al 2019;Golden-Marx et al 2019;Moravec et al 2020b). For example, the Clusters Around Radio Loud AGN (CARLA) survey found that ≈ 55% of their 387 radio loud AGNs at 1.3 < z < 3.2 were in overdense environments at the level of 2σ, with 10% of sources in overdense environments at the 5σ level when compared to a background field (Wylezalek et al 2013).…”

“…More importantly, radio AGNs trace clusters with strong red sequences as well as clusters hosting younger stellar populations and dusty, star-forming galaxies, making radio AGNs an excellent tracer of clusters of all types (Cooke et al 2016;Noirot et al 2016Noirot et al , 2018Golden-Marx et al 2019). Although there are a number of studies of the environments of radio AGN at low redshift (z < 0.5; Best 2000; Croston et al 2019;Garon et al 2019) and high redshift (z > 1.0; e.g., Wylezalek et al 2013;Moravec et al 2019Moravec et al , 2020b, there is need for a sample to both fill the gap between and overlap with these surveys to better trace the evolution of these systems.…”

“…One unique type of radio source that allows for a cluster sample across all ranges of cluster mass and morphology are bent, double-lobed radio sources (e.g., Blanton et al 2000Blanton et al , 2001Blanton et al , 2003Blanton et al , 2015Paterno-Mahler et al 2017;Silverstein et al 2018;Garon et al 2019;Golden-Marx et al 2019). Unlike their straight counterparts, the "C" shape of these radio sources hints at the presence of a dense, gaseous medium acting on the radio source.…”