Why are there strong radio AGNs in the center of "non-cool core" clusters?

TL;DR

This study shows that all strong radio AGNs in galaxy clusters are associated with small X-ray cool cores, called coronae, challenging the traditional cool core/noncool core classification and highlighting the importance of small-scale structures in AGN fueling.

Contribution

It demonstrates that strong radio AGNs in non-cool core clusters are linked to small X-ray cool cores, redefining the cool core classification based on X-ray luminosity distribution.

Findings

All strong radio AGNs are associated with X-ray cool cores.

Small coronae of <5 kpc size fuel radio AGNs in noncool core clusters.

The cool core classification should consider the distribution of X-ray luminosity.

Abstract

Radio AGN feedback in X-ray cool cores has been proposed as a crucial ingredient in the evolution of baryonic structures. However, it has long been known that strong radio AGNs also exist in "noncool core" clusters, which brings up the question whether an X-ray cool core is always required for radio feedback. We present a systematic analysis of 152 groups and clusters to show that every BCG with a strong radio AGN has an X-ray cool core. Those strong radio AGNs in the center of the "noncool core" systems identified before are in fact associated with small X-ray cool cores with typical radii of < 5 kpc (we call them coronae). Small coronae are most likely of ISM origin and they carry enough fuel to power radio AGNs. Our results suggest that the traditional cool core/noncool core dichotomy is too simple. A better alternative is the cool core distribution function with the enclosed X-ray luminosity. Other implications of our results are also discussed, including a warning on the simple extrapolation of the density profile to derive Bondi accretion rate.