From galaxy-scale fueling to nuclear-scale feedback: the merger-state of radio galaxies 3C293, 3C305 & 4C12.50

TL;DR

This study investigates the merger history and gas distribution of three young or re-started radio galaxies with powerful outflows, linking galaxy interactions to feedback processes at different merger stages using optical and HI observations.

Contribution

It provides new detailed optical and HI data on the merger states and gas environments of 3C 293, 3C 305, and 4C 12.50, revealing their complex merger histories and gas distributions.

Findings

All three galaxies show optical tidal features indicating recent mergers.

Different merger stages are identified: pre-coalescent, post-coalescent, and ongoing interaction.

Cold gas is concentrated within the host galaxies, not along tidal features.

Abstract

Powerful radio galaxies are often associated with gas-rich galaxy mergers. These mergers may provide the fuel to trigger starburst and active galactic nuclear (AGN) activity. In this Research Note, we study the host galaxies of three seemingly young or re-started radio sources that drive fast outflows of cool neutral hydrogen (HI) gas, namely 3C 293, 3C 305 and 4C 12.50 (PKS 1345+12). Our aim is to link the feedback processes in the central kpc-scale region with new information on the distribution of stars and gas at scales of the galaxy. For this, we use deep optical V-band imaging of the host galaxies, complemented with HI emission-line observations to study their gaseous environments. We find prominent optical tidal features in all three radio galaxies, which confirm previous claims that 3C 293, 3C 305 and 4C 12.50 have been involved in a recent galaxy merger or interaction. Our data show the complex morphology of the host galaxies, and identify the companion galaxies that are likely involved in the merger or interaction. The radio sources appear to be (re-)triggered at a different stage of the merger; 4C 12.50 is a pre-coalescent and possibly multiple merger, 3C 293 is a post-coalescent merger that is undergoing a minor interaction with a close satellite galaxy, while 3C 305 appears to be shaped by an interaction with a gas-rich companion. For 3C 293 and 3C 305, we do not detect HI beyond the inner ~30-45 kpc region, which shows that the bulk of the cold gas is concentrated within the host-galaxy, rather than along the widespread tidal features.