Hot Gas Flows on Parsec Scale in the Low-Luminosity Active Galactic Nucleus NGC 3115

TL;DR

This study uses two-dimensional hydrodynamical simulations tailored for NGC 3115 to investigate hot gas flows on parsec scales, revealing how local galaxy properties influence accretion onto the supermassive black hole.

Contribution

It provides a detailed simulation-based analysis of accretion flows in NGC 3115, confirming the applicability of radiatively inefficient accretion flow theory and identifying the stagnation radius.

Findings

Flow properties are determined by local galaxy conditions.

A stagnation radius of about 0.1 times the Bondi radius divides inflow and outflow.

Inside the stagnation radius, accretion follows radiatively inefficient flow theory.

Abstract

NGC 3115 is known as the low-luminosity active galactic nucleus which hosts the nearest ($z\sim0.002$) billion solar mass supermassive black hole ($\sim1.5\times10^9~M_\odot$). Its Bondi radius $r_\mathrm{B}$ ($\sim3\farcs6$) can be readily resolved with Chandra, which offers us an excellent opportunity to investigate the accretion flow onto a supermassive black hole. In this paper, we perform two-dimensional hydrodynamical numerical simulations, tailored for NGC 3115, on the mass flow across the Bondi radius. Our best fittings for the density and temperature agree well with the observations of the hot interstellar medium in the centre of NGC 3115. We find that the flow properties are solely determined by the local galaxy properties in the galaxy centre: (1) stellar winds (including supernova ejecta) supply the mass and energy sources for the accreting gas; (2) similar to the one-dimensional calculations, a stagnation radius $r_\mathrm{st}\sim0.1~r_\mathrm{B}$ is also found in the two-dimensional simulations, which divides the mass flow into an inflow-outflow structure; (3) the radiatively inefficient accretion flow theory applies well inside the stagnation radius, where the gravity is dominated by the supermassive black hole and the gas is supported by rotation; (4) beyond the stagnation radius, the stellar gravity dominates the spherical-like fluid dynamics and causes the transition from a steep density profile outside to a flat density profile inside the Bondi radius.