Gas flows in an active galactic nucleus – I. Two-phase gas inflow

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>We perform two-dimensional hydrodynamic simulations to study the non-rotating gas flow in the region from 1 to 1000 pc. This region connects the galaxy scale and the accretion disc scale. The gas is irradiated by the photons generated by the accretion disc system near the central black hole with 108 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.</jats:p>

Dynamical and thermal properties of the parsec-scale gases spherically accreted onto low luminous active galactic nuclei

“…Proga 2007;Proga et al 2008;Kurosawa & Proga 2009;Ramírez-Velásques et al 2019). When Compton scattering force of UV photons is included, Bu, Yang & Zhu(2020) have also observed thermal instability from numerical simulations.…”

“…( 4) Thermal instability may occur in the parsecscale gas irradiated by the accretion disk around SMBHs and then influences the dynamics and thermodynamics of spherical accretion (e.g. Ostriker et al 1976;Cowie et al 1978;Krolik & London 1983;Moscibrodzka & Proga 2013;Waters & Proga 2019;Dannen et al 2020;Bu, Yang & Zhu 2020). The irradiated parsec-scale gas by AGNs could become into a two-phase/cold-hot accretion flow due to thermal instability (Moscibrodzka & Proga 2013;Bu, yang & Zhu 2020), which is interesting to understand the material feeding of AGNs.…”

“…Ostriker et al 1976;Cowie et al 1978;Krolik & London 1983;Moscibrodzka & Proga 2013;Waters & Proga 2019;Dannen et al 2020;Bu, Yang & Zhu 2020). The irradiated parsec-scale gas by AGNs could become into a two-phase/cold-hot accretion flow due to thermal instability (Moscibrodzka & Proga 2013;Bu, yang & Zhu 2020), which is interesting to understand the material feeding of AGNs. Thermal instability may be important not only in the parsec-scale (e.g.…”

“…Thermal instability may be important not only in the parsec-scale (e.g. Moscibrodzka & Proga 2013;Bu, Yang & Zhu 2020) but also in the kpc-scale or the intracluster/circumgalactic medium (e.g. McCourt et al 2012;Choudhury & Sharma 2015;Sobacchi & Sormani 2019;Choudhury et al 2019;Das et al 2021).…”

Jets and spectral states with three-components of accretion flow around a black hole

“…It is natural that the accreting gas at outer AB can has non-uniform temperature distribution. Recently, formation of two-phase (cold gas surrounded by hot gas) inflow gas due to a thermal instability has been investigated very far away from the BH (Bu et al 2020).…”