Hot gas flows on a parsec scale in the low-luminosity active galactic nucleus NGC 3115

Abstract

ABSTRACT NGC 3115 is known as the low-luminosity active galactic nucleus that hosts the nearest (z ∼ 0.002) billion-solar-mass supermassive black hole (∼1.5 × 109 M⊙). Its Bondi radius rB (∼3.6 arcsec) can be readily resolved with Chandra, which provides an excellent opportunity to investigate the accretion flow on to 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 determined solely 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 in the one-dimensional calculations, a stagnation radius rst ∼ 0.1 rB 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.