RAD@home citizen science discovery of an AGN spewing a large unipolar radio bubble onto its merging companion galaxy

TL;DR

This paper reports the discovery of a unique large radio bubble caused by an AGN jet in a galaxy merger, revealing complex jet-gas interactions and raising questions about feedback mechanisms.

Contribution

First imaging study of RAD12 showing a symmetric radio bubble from an AGN jet interacting with a merging galaxy, discovered through citizen science.

Findings

Radio bubble ~137 kpc in size from AGN jet

Symmetric reflection of the bubble after hitting the galaxy

Absence of positive feedback or radio lobe on the opposite side

Abstract

AGN feedback during galaxy merger has been the most favoured model to explain black hole-galaxy co-evolution. However, how the AGN-driven jet/wind/radiation is coupled with the gas of the merging galaxies, which leads to positive feedback, momentarily enhanced star formation, and subsequently negative feedback, a decline in star formation, is poorly understood. Only a few cases are known where the jet and companion galaxy interaction leads to minor off-axis distortions in the jets and enhanced star formation in the gas-rich minor companions. Here, we briefly report one extraordinary case, RAD12, discovered by RAD@home citizen science collaboratory, where for the first time a radio jet-driven bubble ~137 kpc is showing a symmetric reflection after hitting the incoming galaxy which is not a gas-rich minor but a gas-poor early-type galaxy in a major merger. Surprisingly, neither positive feedback nor any radio lobe on the counter jet side, if any, is detected. It is puzzling if RAD12 is a genuine one-sided jet or a case of radio lobe trapped, compressed and re-accelerated by shocks during the merger. This is the first imaging study of RAD12 presenting follow-up with the GMRT, archival MeerKAT radio data and CFHT optical data.