Gas flows in an Active galactic nuclei. I. Two-phase gas inflow

TL;DR

This study uses hydrodynamic simulations to explore two-phase gas inflow in active galactic nuclei, revealing thermal instability at certain densities and quantifying the ratio of cold to hot gas accretion rates.

Contribution

It provides the first detailed analysis of two-phase gas flow in AGN regions connecting galaxy and accretion disk scales, highlighting thermal instability effects.

Findings

Gas with density > 10^{-24} g/cm^3 is thermally unstable.

The cold-to-hot gas accretion ratio can reach up to 16.

Gas below 10^{-24} g/cm^3 remains thermally stable.

Abstract

We perform two-dimensional hydrodynamic simulations to study the non-rotating gas flow in the region from 1-1000 parsec. This region connects the galaxy scale and the accretion disk scale. The gas is irradiated by the photons generated by the accretion disk system near the central black hole with $10^8$ solar mass. We assume that the luminosity of the central accretion system is constant and equals to $0.3$ Eddington luminosity. Gas with density higher than $10^{-24} {\rm g \ cm^{-3}}$ is found to be thermally unstable. Two phase, cold and hot, gas flow will form due to thermal instability. We calculated the ratio of cold gas accretion rate to hot gas accretion rate. This ratio is a function of gas density and generally increases with the increase of gas density. The maximum value of this ratio is $16$, when gas density is $10^{-21} {\rm g \ cm^{-3}} $. Gas with density lower than $10^{-24} {\rm g \ cm^{-3}}$ is found to be thermally stable and the gas flow is one-phase. The applications of the results are briefly discussed.