AGN Feedback in Galaxy Groups: the two interesting cases of AWM 4 and NGC 5044

TL;DR

This paper investigates AGN feedback mechanisms in galaxy groups AWM 4 and NGC 5044, revealing complex interactions between AGN activity, cool cores, and gas dynamics, with new observations of cold fronts and cool coronae.

Contribution

It provides new insights into AGN feedback in galaxy groups, including the discovery of a cool corona in AWM 4 and cold fronts in NGC 5044, challenging existing paradigms.

Findings

AWM 4 has a flat temperature profile but active radio lobes, indicating recent feeding despite lack of cool core.

NGC 5044 exhibits cavities, filaments, and cold fronts, showing complex AGN-driven gas dynamics.

Dust-assisted cooling may play a role in the thermal evolution of the gas.

Abstract

We present AGN feedback in the interesting cases of two groups: AWM 4 and NGC 5044. AWM 4 is characterized by a combination of properties which seems to defy the paradigm for AGN heating in cluster cores: a flat inner temperature profile indicative of a past, major heating episode which completely erased the cool core, as testified by the high central cooling time (> 3 Gyrs) and by the high central entropy level (~ 50 keV cm^2), and yet an active central radio galaxy with extended radio lobes out to 100 kpc, revealing recent feeding of the central massive black hole. A recent Chandra observation has revealed the presence of a compact cool corona associated with the BCG, solving the puzzle of the apparent lack of low entropy gas surrounding a bright radio source, but opening the question of its origin. NGC 5044 shows in the inner 10 kpc a pair of cavities together with a set of bright filaments. The cavities are consistent with a recent AGN outburst as also indicated by the extent of dust and H_alpha emission even though the absence of extended 1.4 GHz emission remains to be explained. The soft X-ray filaments coincident with H_alpha and dust emission are cooler than those which do not correlate with optical and infrared emission, suggesting that dust-aided cooling can contribute to the overall cooling. For the first time sloshing cold fronts at the scale of a galaxy group have been observed in this object.