Shock-accelerated cosmic rays and streaming instability in the adaptive mesh refinement code Ramses

Abstract

Cosmic rays (CRs) are supposed to play a dynamical important role on several key aspects of galaxy evolution, including the structure of the interstellar medium, the formation of galactic winds, and the non-thermal pressure support of halos. We introduce a numerical model solving for the CR streaming instability and acceleration of CRs at shocks with a fluid approach in the adaptive mesh refinement code ramses. CR streaming is solved with a diffusion-like approach and its anisotropic nature is naturally captured. We introduce a shock finder for the ramses code that automatically detects shock discontinuities in the flow. Shocks are the loci for CR injection, and their efficiency of CR acceleration is made dependent of the upstream magnetic obliquity according to the diffuse shock acceleration mechanism. We show that the shock finder accurately captures shock locations and estimates the shock Mach number for several problems. The obliquity-dependent injection of CRs in the Sedov solution leads to situations where the supernova bubble exhibits large polar caps (homogeneous background magnetic field), or a patchy structure of the CR distribution (inhomogeneous background magnetic field). Finally, we combine both accelerated CRs with streaming in a simple turbulent interstellar medium box, and show that the presence of CRs significantly modify the structure of the gas.

Protostellar collapse: the conditions to form dust-rich protoplanetary disks

“…With a proper refinement criteria, the AMR grid is a powerful tool to study multi-scale problems such as the protostellar collapse of a dense core. The RAMSES code is very proficient for problems that require a treatment of magnetohydrodynamics (Teyssier et al 2006;Masson et al 2012;Marchand et al 2018;Marchand et al 2019), radiation hydrodynamics Rosdahl et al 2013;Commerçon et al 2014;Rosdahl & Teyssier 2015;González et al 2015;Mignon-Risse et al 2020) or cosmic rays (Dubois & Commerçon 2016;Dubois et al 2019). We extended the code to the treatment of dust dynamics with multiple species in the diffusion approximation and terminal velocity regime (Lebreuilly et al 2019).…”

Simulations of cosmic ray propagation

“…It has been demonstrated that stable numerical solutions are achievable due to the regularization. Uhlig et al (2012) and later on Dubois et al (2019) showed that streaming can be recasted into a diffusion term and be solved with an implicit solver for diffusion. The streaming transport term in the CR energy equation $…”

“…This result is independent of the assumed magnetic coherence length. Dubois et al (2019) use a similar approach to inject CRs at the loci of the MHD shocks with an on-the-fly shock finder in the larger boxes of the interstellar medium using RAMSES. The efficiency is also coupled to the upstream magnetic obliquity.…”

The impact of astrophysical dust grains on the confinement of cosmic rays

“…turbulence damping). Of course, there exist a variety of complexities in the above argument that make it highly uncertain; however, it seems likely that such questions may only be answered definitively with detailed simulations of the streaming instability, which are only recently becoming possible (Bai et al 2019;Dubois et al 2019;Haggerty & Caprioli 2019;Holcomb & Spitkovsky 2019;Weidl, Winske & Niemann 2019).…”