Non-thermal emission in galaxy groups at extremely low frequency: the case of A1213

Abstract

Galaxy clusters and groups are the last link in the chain of hierarchical structure formation. Their environments can be significantly affected by outbursts from AGN, especially in groups where the medium density is lower and the gravitational potential shallower. The interaction between AGN and group weather can therefore greatly impact their evolution. We investigate the non-thermal radio emission in Abell 1213, a galaxy group which is part of a larger sample of ~50 systems (X-GAP) recently granted XMM-Newton observations. We exploit proprietary LOFAR 54 MHz and uGMRT 380 MHz observations, complementing them with 144 MHz LOFAR survey and XMM-Newton archival data. A1213 hosts a bright AGN associated with one of the central members, 4C 29.41, which was previously optically identified as a dumb-bell galaxy. Observations at 144 MHz at a resolution of 0.3'' allow us to resolve the central radio galaxy. From this source, a ~500 kpc-long tail extends North-East. Our analysis suggests that the tail likely originated from a past outburst of 4C 29.41, and its current state might be the result of the interaction with the surrounding environment. The plateau of the spectral index distribution in the Easternmost part of the tail suggests mild particle re-acceleration, that could have re-energised seed electrons from the past activity of the AGN. While we observe a spatial and physical correlation of the extended, central emission with the thermal plasma, which might hint at a mini-halo, current evidence cannot conclusively prove this. A1213 is only the first group, among the X-GAP sample, that we are able to investigate through low-frequency radio observations. Its complex environment once again demonstrates the significant impact that the interplay between thermal and non-thermal processes can have on galaxy groups.