Inconsistencies arising from the coupling of galaxy formation sub-grid models to pressure-smoothed particle hydrodynamics

ABSTRACT Smoothed particle hydrodynamics (SPH) is a Lagrangian method for solving the fluid equations that commonplace in astrophysics, prized its natural adaptivity and stability. The choice of variable to smooth SPH has been topic contention, with smoothed pressure (P-SPH) being introduced reduce errors at contact discontinuities relative density schemes. schemes produce excellent results isolated tests; more complex situations however, especially when coupling ‘sub-grid’ physics multiple time-stepping used many state-of-the-art astrophysics simulations, these large force can easily evade detection as they do not manifest energy non-conservation. Here, two scenarios are evaluated: injection into (common stellar feedback) radiative cooling. In former scenario, conservation (of same order injected energy), latter change rapidly over few time-steps lead instability lost cooling). Potential ways remedy issues explored solutions generally leading increases computational cost. Schemes using density-based formulation create instabilities such it recommended preferred pressure-based combined an diffusion term discontinuities.