An Analysis Framework for Understanding the Origin of Nuclear Activity
  in Low-Power Radio Galaxies
  Using large samples containing nearly $2300$ active galaxies of low radio
luminosity (1.4 GHz luminosity between $2\times 10^{23}$ and $3\times 10^{25}$
W/Hz, essentially low-excitation radio galaxies) at $z\lesssim 0.3$, we present
a self-contained analysis of the dependence of the nuclear radio activity on
both intrinsic and extrinsic properties of galaxies, with the goal of
identifying the best predictors of the nuclear radio activity. While confirming
the established result that stellar mass must play a key role in the triggering
of radio activities, we point out that for central, most massive galaxies, the
radio activity also shows a strong dependence on halo mass, which is unlikely
due to enhanced interaction rates in denser regions in massive, cluster-scale
halos. We thus further investigate the effects of various properties of the
intracluster medium (ICM) in massive clusters on the radio activities,
employing two standard statistical tools, Principle Component Analysis and
Logistic Regression. It is found that ICM entropy, local cooling time, and
pressure are the most effective in predicting the radio activity, pointing to
the accretion of gas cooling out of a hot atmosphere to be the likely origin in
triggering such activities in galaxies residing in massive dark matter halos.
Our analysis framework enables us to logically discern the mechanisms
responsible for the radio activity separately for central and satellite
galaxies.
