SPH Simulations of Black Hole Accretion: A Step to Model Black Hole Feedback in Galaxies

TL;DR

This study evaluates the accuracy of SPH simulations in modeling black hole accretion and feedback, demonstrating that with proper handling of artificial viscosity, SPH can effectively simulate radiative feedback effects in galactic environments.

Contribution

It provides a detailed assessment of SPH code GADGET-3's ability to reproduce Bondi accretion and feedback processes, highlighting the impact of artificial viscosity on simulation accuracy.

Findings

SPH can replicate Bondi accretion profiles within certain timescales.

Radiative heating delays the attainment of steady-state accretion.

Artificial viscosity causes overheating near the inner radius, but does not affect mass accretion rates.

Abstract

(Abridged) We test how accurately the smoothed particle hydrodynamics (SPH) numerical technique can follow spherically-symmetric Bondi accretion. Using the 3D SPH code GADGET-3, we perform simulations of gas accretion onto a central supermassive black hole (SMBH) of mass 10^8 M_sun within the radial range of 0.1 - 200 pc. We carry out simulations without and with radiative heating by a central X-ray corona and radiative cooling. For an adiabatic case, the radial profiles of hydrodynamical properties match the Bondi solution, except near the inner and outer radius of the computational domain. We find that adiabatic Bondi accretion can be reproduced for durations of a few dynamical times at the Bondi radius, and for longer times if the outer radius is increased. With radiative heating and cooling included, the spherically accreting gas takes a longer time to reach a steady-state than the adiabatic Bondi accretion runs, and in some cases does not reach a steady-state even within several hundred dynamical times. We find that artificial viscosity in the GADGET code causes excessive heating near the inner radius, making the thermal properties of the gas inconsistent with a physical solution. This overheating occurs typically only in the supersonic part of the flow, so that it does not affect the mass accretion rate. We see that increasing the X-ray luminosity produces a lower central mass inflow rate, implying that feedback due to radiative heating is operational in our simulations. With a sufficiently high X-ray luminosity, the inflowing gas is radiatively heated up, and an outflow develops. We conclude that the SPH simulations can capture the gas dynamics needed to study radiative feedback provided artificial viscosity alters only highly supersonic part of the inflow.