The XXL Survey: XXXIV. Double irony in XXL-North. A tale of two radio
  galaxies in a supercluster at z = 0.14
  We show how the XXL multiwavelength survey can be used to shed light on radio
galaxies and their environment. Two prominent radio galaxies were identified in
a visual examination of the mosaic of XXL-North obtained with the Giant
Metrewave Radio Telescope at 610MHz. 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. Both radio galaxies are of FR I 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 about 400 kpc; it is located in the cluster
XLSSC112, which has a temperature of about 2 keV, a total mass of about
$10^{14} M_\odot$, and resides in an XXL supercluster with eight known members.
The second source, named the Double Irony, is a giant radio galaxy with a total
length of about 1.1 Mpc. 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
Double Irony's group is a member of the same supercluster as the Exemplar.
There are indications that the jets and plumes of the Double Irony 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. Radio galaxies can be used to find galaxy
clusters/groups that are below the current sensitivity of X-ray surveys.
