Comparing energy and entropy formulations for cosmic ray hydrodynamics

• DOI: 10.1093/mnras/stac3781
• Publication Date: 2022-12-24T00:49:56Z
• Authors: Matthias Weber; Timon Thomas; Christoph Pfrommer
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); 0103 physical sciences; FOS: Physical sciences; Astrophysics - High Energy Astrophysical Phenomena; 01 natural sciences

Cosmic rays (CRs) play an important role in many astrophysical systems. Acting on plasma scales to galactic environments, CRs are usually modeled as a fluid, using the CR energy density evolving quantity. This method comes with flaw that corresponding evolution equation is not conservative form it contains adiabatic source term couples thermal gas. In absence of non-adiabatic changes, instead entropy physically equivalent option avoids this potential numerical inconsistency. work, we study both approaches for context magneto-hydrodynamic (MHD) simulations massively parallel moving-mesh code AREPO. We investigate performance methods sequence shock-tube tests various resolutions and shock Mach numbers. find entropy-conserving scheme performs best idealized case purely across while yield similar results at lower resolution. setup, schemes operate well almost independently number. Taking active acceleration into account, energy-based proves be numerically much more stable significantly accurate determining velocity, particular low resolution, which typical large-scale simulations. For realistic application, simulate formation several isolated galaxies different halo masses identical differences far below common uncertainties.