Massive Molecular Gas as a Fuel Tank for Active Galactic Nuclei Feedback in Central Cluster Galaxies

TL;DR

This paper presents a semianalytical model demonstrating that massive molecular gas in central cluster galaxies acts as a fuel reservoir for AGN activity, influencing feedback processes and galaxy evolution.

Contribution

It introduces a novel model linking molecular gas dynamics, disk stability, and AGN feedback, highlighting the role of cold gas as a sustained fuel source.

Findings

Massive molecular gas can sustain AGN activity for over 0.5 Gyr.

Circumnuclear disks tend to hover at the boundary of stability, regulating black hole accretion.

Low entropy hot gas or short cooling times are critical for large molecular gas reservoirs.

Abstract

Massive molecular gas has been discovered in giant elliptical galaxies at the centers of galaxy clusters. To reveal its role in active galactic nucleus (AGN) feedback in those galaxies, we construct a semianalytical model of gas circulation. This model especially focuses on the massive molecular gas (interstellar cold gas on a scale of ~ 10 kpc) and the circumnuclear disk (~< 0.5 kpc). We consider the destruction of the interstellar cold gas by star formation and the gravitational instability for the circumnuclear disk. Our model can reproduce the basic properties of the interstellar cold gas and the circumnuclear disk, such as their masses. We also find that the circumnuclear disk tends to stay at the boundary between stable and unstable states. This works as an 'adjusting valve' that regulates mass accretion toward the supermassive black hole. On the other hand, the interstellar cold gas serves as a 'fuel tank' in the AGN feedback. Even if the cooling of the galactic hot gas is prevented, the interstellar cold gas can sustain the AGN activity for ~> 0.5 Gyr. We also confirm that the small entropy of the hot gas (~< 30 keV cm^2) or the short cooling time (~< 1 Gyr) is a critical condition for the existence of the massive amounts of molecular gas in the galaxy. The dissipation time of the interstellar cold gas may be related to the critical cooling time. The galaxy behavior is described by a simple relation among the disk stability, the cloud dissipation time, and the gas cooling rate.