Shock-accelerated cosmic rays and streaming instability in the adaptive mesh refinement code Ramses: methods and tests. (arXiv:1907.04300v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Dubois_Y/0/1/0/all/0/1">Yohan Dubois</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Commercon_B/0/1/0/all/0/1">Benoît Commerçon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marcowith_A/0/1/0/all/0/1">Alexandre Marcowith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brahimi_L/0/1/0/all/0/1">Loann Brahimi</a>
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.
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.
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