A Study of High-redshift AGN Feedback in SZ Cluster Samples
  We present a study of AGN feedback at higher redshifts ($0.3<z<1.2$) using
Sunyaev-Zel'dovich (SZ) selected samples of clusters from the South-Pole
Telescope and Atacama Cosmology Telescope surveys. In contrast to studies of
nearby systems, we do not find a separation between cooling flow clusters and
non-cooling flow clusters based on the radio luminosity of the central radio
source. This lack may be due to the increased incidence of galaxy-galaxy
mergers at higher redshift that triggers AGN activity. In support of this
scenario, we find evidence for evolution in the radio luminosity function of
the central radio source: while the lower-luminosity sources do not evolve
much, the higher-luminosity sources show a strong increase in the frequency of
their occurrence at higher redshifts. We interpret this evolution as an
increase in high-excitation radio galaxies (HERGs) in massive clusters at
$z>0.6$, implying a transition from HERG-mode accretion to lower-power
low-excitation radio galaxy (LERG)-mode accretion at intermediate redshifts.
Additionally, we use local radio-to-jet power scaling relations to estimate
feedback power and find that half of the cooling flow systems in our sample
probably have enough heating to balance cooling. However, we postulate that the
local relations are likely not well suited to predict feedback power in
high-luminosity HERGs, as they are derived from samples composed mainly of
lower-luminosity LERGs.
