An Analysis Framework for Understanding the Origin of Nuclear Activity in Low-Power Radio Galaxies

TL;DR

This study develops an analysis framework to identify key galaxy and cluster properties, such as stellar mass and intracluster medium characteristics, that influence low-power radio galaxy activity, highlighting gas cooling as a trigger.

Contribution

It introduces a comprehensive framework combining statistical tools to distinguish mechanisms driving nuclear radio activity in different galaxy types.

Findings

Stellar mass is crucial for radio activity triggering.

Halo mass influences activity in massive central galaxies.

ICM properties like entropy and pressure predict radio activity.

Abstract

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.