Presentation #101.07 in the session Galaxy Clusters/Large Scale Structures.
The ultimate fate of the gas cooling in the centers of clusters and groups is as yet not fully understood. Owing to their rapid cooling rates and shallow gravitational potentials, galaxy groups appear to be some of the most interesting objects in which to study AGN feedback. While NGC5044, the X-ray brightest group in the sky, is the archetype of cooling flow galaxy groups, NGC6338 is the most violent group-group merger known to date. We give an overview of the AGN feedback process in these two very different galaxy groups, and use a multi-wavelength approach to examine the gas recycling from macroscopic scales of hundreds of kiloparsecs down to parsecs. Interestingly, the BCGs in both galaxy groups are rare, but prominent cases where the direction of jet-mode feedback between two cycles has changed dramatically.
The cool-core galaxy group, NGC5044, hosts the largest known reservoir of cold gas of any X-ray luminous group, and shows evidence of three past epochs of AGN feedback. We have acquired a wealth of multi-wavelength data to investigate the supply of cold gas, and the past and current feedback status. With high resolution radio data, we image the smallest scales around the central supermassive black hole itself, and model the SED with an advection dominated accretion flow. At mm wavelengths the AGN is variable on timescales of several months, which we link to changes in the accretion rate.
The violent environment in NGC6338 shows dramatic gas heating and shock fronts, caused by 1400km/s merger along the line of sight. However, the central gas in the BCGs remains cool, neither subcluster core has been disrupted, and both show indications of feedback from their AGN. In deep uGMRT radio observations we clearly detect a pair of large, old lobes in the southern BCG coinciding with X-ray cavities, as well as a smaller, younger pair, perpendicular to the larger lobes, but coinciding with inner X-ray cavities and matching the jet direction in the parsec-scale resolution VLBA image. The high radio frequency analysis classifies the compact source in the southern BCG with a powerlaw, while ruling out a significant contribution from ongoing accretion.