Numerical overcooling in shocks

TL;DR

This paper investigates numerical overcooling in radiative shock simulations using SPH and AMR codes, providing a resolution criterion to prevent overcooling in cosmological and galactic feedback scenarios.

Contribution

It derives a similarity solution for radiative shocks and tests the impact of numerical schemes on overcooling, offering practical resolution guidelines for realistic simulations.

Findings

Overcooling is linked to shock broadening caused by numerical schemes.

A resolution of 10^6 M_sun per particle/cell prevents overcooling in cosmological shocks.

High-temperature bubbles (>10^7 K) are needed to accurately model supernova and AGN feedback.

Abstract

We present a study of cooling in radiative shocks simulated with smoothed particle hydrodynamics (SPH) and adaptive mesh refinement codes. We obtain a similarity solution for a shock-tube problem in the presence of radiative cooling, and test how well the solution is reproduced in Gadget and Flash. Shock broadening governed by the details of the numerical scheme (artificial viscosity or Riemann solvers) leads to potentially significant overcooling in both codes. We interpret our findings in terms of a resolution criterion, and apply it to realistic simulations of cosmological accretion shocks onto galaxy haloes, cold accretion and thermal feedback from supernovae or active galactic nuclei. To avoid numerical overcooling of accretion shocks onto haloes that should develop a hot corona requires a particle or cell mass resolution of 10^6 M_sun, which is within reach of current state-of-the-art simulations. At this mass resolution, thermal feedback in the interstellar medium of a galaxy requires temperatures of supernova or AGN driven bubbles to be in excess of 10^7 K at densities of n_H=1.0 cm^-3, in order to avoid spurious suppression of the feedback by numerical overcooling.