The extraordinary radio galaxy MRC B1221-423: probing deeper at radio and optical wavelengths

TL;DR

This study provides detailed optical and radio observations of the young, powerful radio galaxy MRC B1221-423, revealing its interaction with the environment, distorted jet morphology, and ongoing star formation, indicating a recent AGN activation in a gas-rich system.

Contribution

It offers new multi-wavelength data showing the interaction between the AGN and its environment, and details the timing of star formation and AGN triggering in a young radio galaxy.

Findings

Distorted radio jet morphology due to interaction with host galaxy

Presence of infalling gas and strong absorption features

Concurrent star formation and AGN activity with a time delay

Abstract

We present optical spectra and high-resolution multi-wavelength radio observations of the compact steep-spectrum radio source MRC B1221-423 (z=0.1706). MRC B1221-423 is a very young (~10^5 yr), powerful radio source which is undergoing a tidal interaction with a companion galaxy. We find strong evidence of interaction between the AGN and its environment. The radio morphology is highly distorted, showing a dramatic interaction between the radio jet and the host galaxy, with the jet being turned almost back on itself. H I observations show strong absorption against the nucleus at an infall velocity of ~250 km/s compared to the stellar velocity, as well as a second, broader component which may represent gas falling into the nucleus. Optical spectra show that star formation is taking place across the whole system. Broad optical emission lines in the nucleus show evidence of outflow. Our observations confirm that MRC B1221-423 is a young radio source in a gas-rich nuclear environment, and that there was a time delay of a few x 100 Myr between the onset of star formation and the triggering of the AGN.