The dust masses of powerful radio galaxies: clues to the triggering of their activity

TL;DR

This study uses Herschel observations to measure dust masses in intermediate-redshift radio galaxies, revealing insights into their AGN triggering mechanisms and the role of galaxy mergers in their evolution.

Contribution

It provides the first comprehensive dust mass estimates for a complete sample of radio galaxies, linking dust content to AGN activity and merger history.

Findings

Most radio galaxies have intermediate dust masses, indicating late-time AGN re-triggering.

Approximately 20% of the sample shows ULIRG-like dust masses and star formation, suggesting major mergers.

Dust masses correlate with different triggering mechanisms and galaxy evolution stages.

Abstract

We use deep Herschel Space Observatory observations of a 90% complete sample of 32 intermediate-redshift 2Jy radio galaxies (0.05 < z < 0.7) to estimate the dust masses of their host galaxies and thereby investigate the triggering mechanisms for their quasar-like AGN. The dust masses derived for the radio galaxies (7.2x10^5 < M_d < 2.6x10^8 M_sun) are intermediate between those of quiescent elliptical galaxies on the one hand, and ultra luminous infrared galaxies (ULIRGs) on the other. Consistent with simple models for the co-evolution of supermassive black holes and their host galaxies, these results suggest that most of the radio galaxies represent the late time re-triggering of AGN activity via mergers between the host giant elliptical galaxies and companion galaxies with relatively low gas masses. However, a minority of the radio galaxies in our sample (~20%) have high, ULIRG-like dust masses, along with evidence for prodigious star formation activity. The latter objects are more likely to have been triggered in major, gas-rich mergers that represent a rapid growth phase for both their host galaxies and their supermassive black holes.