Nikhel Gupta
We study the properties of the Sydney University Molonglo Sky Survey (SUMSS) 843~MHz radio AGN population in galaxy clusters from two large catalogs created using the Dark Energy Survey (DES): $\sim$11,800 optically selected RM-Y3 and $\sim$1,000 X-ray selected MARD-Y3 clusters.
We show that cluster radio loud AGN are highly concentrated around cluster centers to $z\sim1$.
We measure the halo occupation number for cluster radio AGN above a threshold luminosity, finding that the number of radio AGN per cluster increases with cluster halo mass as $N\propto M^{1.2\pm0.1}$ ($N\propto M^{0.68\pm0.34}$) for the RM-Y3 (MARD-Y3) sample.
Together, these results indicate that radio mode feedback is favoured in more massive galaxy clusters.
Using optical counterparts for these sources, we demonstrate weak redshift evolution in the host broad
band colors and the radio luminosity at fixed host galaxy stellar mass.
We use the redshift evolution in radio luminosity to break the degeneracy
between density and luminosity evolution scenarios in the redshift trend of the radio AGN luminosity function (LF).
The LF exhibits a redshift trend of the form $(1+z)^\gamma$ in density and luminosity, respectively, of $\gamma_{\rm D}=3.0\pm0.4$ and $\gamma_{\rm P}=0.21\pm0.15$ in the RM-Y3 sample, and $\gamma_{\rm D}=2.6\pm0.7$ and $\gamma_{\rm P}=0.31\pm0.15$ in MARD-Y3.
We discuss the physical drivers of radio mode feedback in cluster AGN, and we use the cluster radio galaxy LF to estimate the average radio-mode feedback energy as a function of cluster mass and redshift and compare it to the core ($<0.1R_{500}$) X-ray radiative losses for clusters at $z<1$.
These properties of radio AGN include their radial distribution within the cluster, radio luminosity evolution at fixed stellar mass, luminosity functions (LFs) and halo occupation number (HON) above a luminosity threshold. These measurements are made using SUMSS selected sources observed at 843~MHz within optically selected RM-Y3 and X-ray selected MARD-Y3 cluster catalogs
that have been produced using the first three years of DES observations and the RASS X-ray survey.
We focus on the excess population of radio sources associated with the virial regions of these clusters. The median redshifts of RM-Y3 and MARD-Y3 clusters
are 0.47 and 0.28, respectively, and the catalogs extend to z=0.8 and beyond (see Figure 1 for the distributions).
We find that the radial profile of the sources in RM-Y3 and MARD-Y3 catalogs is highly concentrated at the center of the cluster over the whole redshift range and is consistent with an NFW model with concentration c~140 (see Figure 4).
We construct the LFs assuming that the overdensity of radio AGN toward a cluster is at the redshift of the cluster, and we correct for the non-cluster sources by employing a statistical background correction. We find that at fixed cluster halo mass, the cluster radio galaxies are more numerous at higher redshift (see Figure 5 and Table 1).
Furthermore, we estimate the halo occupation number for radio AGN above a fixed luminosity threshold in a stack of RM-Y3 and MARD-Y3 clusters using the LF evolution identified above (see Figure 6).
We go on to use the radio AGN LF to estimate the radio mode feedback as a function of mass and redshift out to z~1 and compare that to the mean core X-ray radiative losses from the ICM at each mass and redshift. The radio mode feedback dominates the core radiative losses in low mass systems and is comparable to or smaller than those radiative losses for systems with high mass over the full redshift range. We note the imbalance of radio mode feedback and X-ray radiative losses is qualitatively consistent with what one would expect to explain the absence of redshift evolution of the cool core population and the trend of increasing ICM mass fraction with mass observed within clusters over the same mass and redshift range (see Figure 7).