Central gas entropy excess as a direct evidence for AGN feedback in galaxy groups and clusters

TL;DR

This study provides observational evidence that active galactic nucleus (AGN) feedback significantly influences the central gas entropy in galaxy groups and clusters, with a strong correlation between entropy excess and the properties of central galaxies.

Contribution

It demonstrates a direct link between central gas entropy excess and AGN feedback, supported by correlations with central galaxy luminosity and black hole mass, using Chandra X-ray data.

Findings

Significant central entropy excess found in 31 systems.

Entropy excess correlates with central galaxy luminosity.

AGN feedback energy can account for the observed entropy excess.

Abstract

By analyzing Chandra X-ray data of a sample of 21 galaxy groups and 19 galaxy clusters, we find that in 31 sample systems there exists a significant central ($R^{<}_{\sim} 10h_{71}^{-1}$ kpc) gas entropy excess ($\Delta K_{0}$), which corresponds to $\simeq 0.1-0.5$ keV per gas particle, beyond the power-law model that best fits the radial entropy profile of outer regions. We also find a distinct correlation between the central entropy excess $\Delta K_{0}$ and $K$-band luminosity $L_{K}$ of the central dominating galaxies (CDGs), which is scaled as $\Delta K_{0} \propto L_{K}^{1.6\pm0.4}$, where $L_{K}$ is tightly associated with the mass of the supermassive black hole hosted in the CDG. In fact, if an effective mass-to-energy conversion-efficiency of 0.02 is assumed for the accretion process, the cumulative AGN feedback $E^{\rm AGN}_{\rm feedback} \simeq \eta M_{\rm BH}c^{2}$ yields an extra heating of $\simeq 0.5-17.0$ keV per particle, which is sufficient to explain the central entropy excess. In most cases the AGN contribution can compensate the radiative loss of the X-ray gas within the cooling radius ($\simeq 0.002-2.2$ keV per particle), and apparently exceeds the energy required to deviate the scaling relations from the self-similar predictions ($\simeq 0.2-1.0$ keV per particle). In contrast to the AGN feedback, the extra heating provided by supernova explosions accounts for $\simeq 0.01-0.08$ keV per particle in groups and is almost negligible in clusters. Therefore, the observed correlation between $\Delta K_{0}$ and $L_{K}$ can be considered as a direct evidence for AGN feedback in galaxy groups and clusters.