2018A&A...620A..19H

Aims. We show how the XXL multiwavelength survey can be used to shed light on radio galaxies and their environment.
Methods. Two prominent radio galaxies were identified in a visual examination of the mosaic of XXL-North obtained with the Giant Metrewave Radio Telescope at 610 MHz. Counterparts were searched for in other bands. Spectroscopic redshifts from the GAMA database were used to identify clusters and/or groups of galaxies, estimate their masses with the caustic method, and quantify anisotropies in the surrounding galaxy distribution via a Fourier analysis.
Results. Both radio galaxies are of FRI type and are hosted by early-type galaxies at a redshift of 0.138. The first radio source, named the Exemplar, has a physical extent of ∼400kpc; it is located in the cluster XLSSC 112, which has a temperature of ∼2keV, a total mass of ∼10¹⁴M_☉, and resides in an XXL supercluster with eight known members. The second source, named the DoubleIrony, is a giant radio galaxy with a total length of about 1.1Mpc.Its core coincides with a cataloged point-like X-ray source, but no extended X-ray emission from a surrounding galaxy cluster was detected. However, from the optical data we determined that the host is the brightest galaxy in a group that is younger, less virialized, and less massive than the Exemplar's cluster. A friends-of-friends analysis showed that the DoubleIrony's group is a member of the same supercluster as the Exemplar. There are indications that the jets and plumes of the DoubleIrony have been deflected by gas associated with the surrounding galaxy distribution. Another overdensity of galaxies (the tenth) containing a radio galaxy was found to be associated with the supercluster.
Conclusions. Radio Galaxies can be used to find galaxy clusters/groups that are below the current sensitivity of X-ray surveys.