On the Mass Loading of AGN-Driven Outflows in Elliptical Galaxies and Clusters

TL;DR

This study models AGN-driven outflows in elliptical galaxies and clusters using a mass-loading factor, constraining outflow properties and revealing efficient coupling and deceleration of outflows on sub-kiloparsec scales.

Contribution

Introduces a simplified model using a single parameter to characterize AGN outflows, constrained by X-ray observations of M87 and Perseus, revealing lower outflow speeds and higher mass-loading than previously thought.

Findings

Outflow-to-accretion mass-loading factor constrained between 200-500

Outflow speeds around 4,000-7,000 km/s at 1 kpc

AGN outflows can be 10 times more massive than cold gas measurements

Abstract

Outflows driven by active galactic nuclei (AGN) are an important channel for accreting supermassive black holes (SMBHs) to interact with their host galaxies and clusters. Properties of the outflows are however poorly constrained due to the lack of kinetically resolved data of the hot plasma that permeates the circumgalactic and intracluster space. In this work, we use a single parameter, outflow-to-accretion mass-loading factor $m=\dot{M}_{\rm out}/\dot{M}_{\rm BH}$, to characterize the outflows that mediate the interaction between SMBHs and their hosts. By modeling both M87 and Perseus, and comparing the simulated thermal profiles with the X-ray observations of these two systems, we demonstrate that $m$ can be constrained between $200-500$. This parameter corresponds to a bulk flow speed between $4,000-7,000\,{\rm km\,s}^{-1}$ at around 1 kpc, and a thermalized outflow temperature between $10^{8.7}-10^{9}\,{\rm K}$. Our results indicate that the dominant outflow speeds in giant elliptical galaxies and clusters are much lower than in the close vicinity of the SMBH, signaling an efficient coupling with and deceleration by the surrounding medium on length scales below 1 kpc. Consequently, AGNs may be efficient at launching outflows $\sim10$ times more massive than previously uncovered by measurements of cold, obscuring material. We also examine the mass and velocity distribution of the cold gas, which ultimately forms a rotationally supported disk in simulated clusters. The rarity of such disks in observations indicates that further investigations are needed to understand the evolution of the cold gas after it forms.