Molecular gas in nearby powerful radio galaxies

TL;DR

This study investigates the molecular gas content in powerful radio galaxies, revealing they have less gas than FIR-selected galaxies and suggesting minor mergers as a fueling mechanism for nuclear activity.

Contribution

It provides the first CO survey of radio-selected powerful radio galaxies, highlighting their low molecular gas content and potential fueling processes.

Findings

Median molecular gas mass is 10^8 Msun.

Significant difference in gas content between FR-I and FR-II galaxies.

Presence of central molecular gas disks suggested by CO spectra.

Abstract

Powerful radio-AGN are normally hosted by massive elliptical galaxies which are usually very poor in molecular gas. Nevertheless the gas is needed in the very center to feed the nuclear activity. Thus it is important to study the origin, the distribution and the kinematics of the molecular gas in such objects. We have performed at the IRAM-30m telescope a survey of the CO(1-0) and CO(2-1) emission in the most powerful radio galaxies of the Local Universe, selected only on the basis of their radio-continuum fluxes. The main result of this survey is the very low content in molecular gas of such galaxies compared to FIR selected galaxies. The median value of the molecular gas mass, taking into account the upper limits, is 1x10^8 Msun; if we calculate it for all the galaxies together, and if we separate them into FR-I and FR-II type galaxies, an important difference is found between them. Moreover, the CO spectra indicates the presence of a central molecular gas disk in these radio galaxies. Our results contrast with previous surveys, mainly selected through the FIR emission, with a larger mass of molecular gas observed. The first results indicate that minor mergers are good candidates to fuel the central part of the radio galaxies of our sample.