Simulating galactic outflows with thermal supernova feedback

TL;DR

This paper introduces a stochastic thermal feedback method for galaxy simulations that effectively suppresses star formation and drives outflows by ensuring injected energy heats gas to a minimum temperature, overcoming radiative losses.

Contribution

The authors propose and validate a new stochastic thermal feedback technique that improves the efficiency of supernova energy injection in galaxy simulations, applicable to both particle and grid codes.

Findings

Strong suppression of star formation in simulated galaxies.

Generation of large-scale outflows without disabling radiative cooling.

Results become resolution-independent at high resolution.

Abstract

Cosmological simulations make use of sub-grid recipes for the implementation of galactic winds driven by massive stars because direct injection of supernova energy in thermal form leads to strong radiative losses, rendering the feedback inefficient. We argue that the main cause of the catastrophic cooling is a mismatch between the mass of the gas in which the energy is injected and the mass of the parent stellar population. Because too much mass is heated, the temperatures are too low and the cooling times too short. We use analytic arguments to estimate, as a function of the gas density and the numerical resolution, the minimum heating temperature that is required for the injected thermal energy to be efficiently converted into kinetic energy. We then propose and test a stochastic implementation of thermal feedback that uses this minimum temperature increase as an input parameter and that can be employed in both particle- and grid-based codes. We use smoothed particle hydrodynamics simulations to test the method on models of isolated disc galaxies in dark matter haloes with total mass 10^10 and 10^12 h^-1 solar masses. The thermal feedback strongly suppresses the star formation rate and can drive massive, large-scale outflows without the need to turn off radiative cooling temporarily. In accord with expectations derived from analytic arguments, for sufficiently high resolution the results become insensitive to the imposed temperature jump and also agree with high-resolution simulations employing kinetic feedback.