Modeling Hot Gas Flow in the Low-Luminosity Active Galactic Nucleus of NGC3115

TL;DR

This study models the hot gas flow in the low-luminosity AGN of NGC3115, integrating stellar processes and feedback mechanisms to explain observed X-ray emissions and gas dynamics around the supermassive black hole.

Contribution

It introduces a comprehensive model of hot gas flow in NGC3115's nucleus, incorporating electron heat conduction, stellar feedback, and gravitational effects, fitting observed X-ray data.

Findings

Best-fitting black hole mass < 1.3×10^9 M_sun

Outflows dominate within 1 arcsec, with most gas escaping the region

Density profile n∝ r^−1 over large scales

Abstract

Based on the dynamical black hole (BH) mass estimates, NGC3115 hosts the closest billion solar mass BH. Deep studies of the center revealed a very underluminous active galactic nucleus (AGN) immersed in an old massive nuclear star cluster. Recent $1$~Ms \textit{Chandra} X-ray visionary project observations of the NGC3115 nucleus resolved hot tenuous gas, which fuels the AGN. In this paper we connect the processes in the nuclear star cluster with the feeding of the supermassive BH. We model the hot gas flow sustained by the injection of matter and energy from the stars and supernova explosions. We incorporate electron heat conduction as the small-scale feedback mechanism, the gravitational pull of the stellar mass, cooling, and Coulomb collisions. Fitting simulated X-ray emission to the spatially and spectrally resolved observed data, we find the best-fitting solutions with $\chi^2/dof=1.00$ for $dof=236$ both with and without conduction. The radial modeling favors a low BH mass $<1.3\times10^{9}M_\odot$. The best-fitting supernova rate and the best-fitting mass injection rate are consistent with their expected values. The stagnation point is at $r_{\rm st}\lesssim1$arcsec, so that most of gas, including the gas at a Bondi radius $r_B=2-4$arcsec, outflows from the region. We put an upper limit on the accretion rate at $2\times10^{-3}M_\odot{\rm yr}^{-1}$. We find a shallow density profile $n\propto r^{-\beta}$ with $\beta\approx1$ over a large dynamic range. This density profile is determined in the feeding region $0.5-10$arcsec as an interplay of four processes and effects: (1) the radius-dependent mass injection, (2) the effect of the galactic gravitational potential, (3) the accretion flow onset at $r\lesssim1$arcsec, and (4) the outflow at $r\gtrsim1$arcsec. The gas temperature is close to the virial temperature $T_v$ at any radius.