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

2019 ◽  
Vol 631 ◽  
pp. A121 ◽  
Author(s):  
Yohan Dubois ◽  
Benoît Commerçon ◽  
Alexandre Marcowith ◽  
Loann Brahimi
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Interstellar Medium ◽  
Galaxy Evolution ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Shock Acceleration ◽  
Streaming Instability ◽  
Background Magnetic Field

Cosmic rays (CRs) are thought to play a dynamically important role in 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 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 on 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 modifies the structure of the gas.

scholarly journals A New Adaptive Mesh Refinement Method in FEA Based on Magnetic Field Conservation at Elements Interfaces and Non-Conforming Mesh Refinement Technique

2017 ◽  
Vol 53 (6) ◽  
pp. 1-4 ◽  
Author(s):  
So Noguchi ◽  
Takuto Naoe ◽  
Hajime Igarashi ◽  
Shinya Matsutomo ◽  
Vlatko Cingoski ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Refinement Method

scholarly journals Cosmological Shocks in Adaptive Mesh Refinement Simulations and the Acceleration of Cosmic Rays

2008 ◽  
Vol 689 (2) ◽  
pp. 1063-1077 ◽  
Author(s):  
Samuel W. Skillman ◽  
Brian W. O’Shea ◽  
Eric J. Hallman ◽  
Jack O. Burns ◽  
Michael L. Norman
Keyword(s):  
Cosmic Rays ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh

Galaxy Evolution with Adaptive Mesh Refinement

2008 ◽  
Author(s):  
Ji‐hoon Kim ◽  
John H. Wise ◽  
Tom Abel
Keyword(s):  
Galaxy Evolution ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh

scholarly journals Electrons in the supernova-driven interstellar medium

2020 ◽  
Vol 644 ◽  
pp. A156
Author(s):  
Miguel A. de Avillez ◽  
Gervásio J. Anela ◽  
Ashish Asgekar ◽  
Dieter Breitschwerdt ◽  
Dominic H. F. M. Schnitzeler
Keyword(s):  
Interstellar Medium ◽  
Adaptive Mesh Refinement ◽  
Electron Distribution ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Vantage Point ◽  
Line Of Sight ◽  
Interstellar Gas ◽  
Volume Analysis ◽  
Dispersion Measures

Context. Interstellar gas is in a highly turbulent dynamic state driven by successive supernova explosions and stellar winds, while its electron distribution is determined by microscopic processes such as ionization and recombination. In order to understand the properties of the electrons in the interstellar medium (ISM) it is necessary to follow numerically the nonlinear spatial and temporal evolution of the gas, its ionization structure, and its emission properties. Aims. We study the time evolution of the electrons in the ISM and how line of sight observations compare to volume analysis of the simulated medium populated with atoms and ions of the ten most abundant species. In particular, we make quantitative predictions about the occupation fractions and averaged densities of electrons, the dispersion measures, and their vantage point dependence. Methods. We carried out state-of-the-art adaptive mesh refinement simulations of the supernova-driven interstellar gas tracing the evolution of 112 ions and atoms of H, He, C, N, O, Ne, Mg, Si, S, and Fe and their emissivities in a time-dependent fashion. The gas is followed with the magnetohydrodynamical adaptive mesh refinement parallel code coupled with the Collisional + Photo Ionization Plasma Emission Software to trace the ionic structure and radiative emission of the plasma. Results. We show that more than 60% of the electrons are in thermally unstable regimes: about 50% at 200 < T ≤ 103.9 K and 14% at 104.2 < T ≤ 105.5 K. The probability density functions for the electron distribution in different temperature regimes is rather broad, also a result of turbulence in the ISM. Comparing the calculated dispersion measures along different lines of sight to observation, we find a very good agreement. They increase linearly for distances greater than 300 pc from the observer at an average rate of 27 cm−3 pc per kpc. The dispersion regarding the average dispersion measures does not decrease with distance along the line of sight, pointing to a high clumpiness of the electrons and of the turbulent ISM. The mean electron density in the Galactic midplane derived from the volume analysis varies between 0.029 and 0.031 cm−3, while that derived from the dispersion measures, varies between 0.0264 and 0.03 cm−3 depending on the vantage point and on the time averaged period. These variations can be as high as 8.3% between vantage points.

scholarly journals Constrained transport and adaptive mesh refinement in the Black Hole Accretion Code

2019 ◽  
Vol 629 ◽  
pp. A61 ◽  
Author(s):  
Hector Olivares ◽  
Oliver Porth ◽  
Jordy Davelaar ◽  
Elias R. Most ◽  
Christian M. Fromm ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Adaptive Mesh Refinement ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Gravitational Fields ◽  
Black Hole Accretion ◽  
Constrained Transport ◽  
The Magnetic Field ◽  
Hole Accretion

Context. Worldwide very long baseline radio interferometry (VLBI) arrays are expected to obtain horizon-scale images of supermassive black hole candidates and of relativistic jets in several nearby active galactic nuclei. This, together with the expected detection of electromagnetic counterparts of gravitational-wave signals, motivates the development of models for magnetohydrodynamic flows in strong gravitational fields. Aims. The Black Hole Accretion Code (BHAC) is a publicliy available code intended to aid with the modeling of such sources by performing general relativistic magnetohydrodynamical simulations in arbitrary stationary spacetimes. New additions to the code are required in order to guarantee an accurate evolution of the magnetic field when small and large scales are captured simultaneously. Methods. We discuss the adaptive mesh refinement (AMR) techniques employed in BHAC, which are essential to keep several problems computationally tractable, as well as staggered-mesh-based constrained transport (CT) algorithms to preserve the divergence-free constraint of the magnetic field. We also present a general class of prolongation operators for face-allocated variables compatible with them. Results. After presenting several standard tests for the new implementation, we show that the choice of the divergence-control method can produce qualitative differences in the simulation results for scientifically relevant accretion problems. We demonstrate the ability of AMR to decrease the computational costs of black hole accretion simulations while sufficiently resolving turbulence arising from the magnetorotational instability. In particular, we describe a simulation of an accreting Kerr black hole in Cartesian coordinates using AMR to follow the propagation of a relativistic jet while self-consistently including the jet engine, a problem set up for which the new AMR implementation is particularly advantageous. Conclusions. The CT methods and AMR strategies discussed here are currently being used in the simulations performed with BHAC for the generation of theoretical models for the Event Horizon Telescope collaboration.

scholarly journals A systematic study of radiative torque grain alignment in the diffuse interstellar medium

2020 ◽  
Vol 640 ◽  
pp. A118 ◽  
Author(s):  
Stefan Reissl ◽  
Vincent Guillet ◽  
Robert Brauer ◽  
François Levrier ◽  
François Boulanger ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Specific Pattern ◽  
Data Cube ◽  
Polarization Angle ◽  
Grain Alignment ◽  
Polarization Fraction ◽  
The Magnetic Field

Context. Analyses of Planck data have demonstrated that the grain alignment efficiency is almost constant in the diffuse and translucent interstellar medium (ISM). Aims. We aim to test whether the radiative torque (RAT) theory is compatible with these new observational constraints on grain alignment. Methods. We combine a numerical magnetohydrodynamical simulation with a state-of-the-art radiative transfer post-processing code POLARIS which incorporates a physical dust model and the detailed physics of grain alignment by RATs. A dust model based on two distinct power-law-sized distributions of spherical graphite grains and oblate silicate grains was designed to reproduce the mean spectral dependence of extinction and polarization observed in the diffuse ISM. From a simulation of interstellar turbulence obtained with the adaptive-mesh-refinement code RAMSES, we extracted a data cube with physical conditions representative of the diffuse ISM. We post-process the RAMSES cube with POLARIS to compute the grain temperature and alignment efficiency in each cell of the cube. Finally, we simulate synthetic dust emission and polarization observations. Results. In our simulation, the grain alignment efficiency is well-correlated with the gas pressure, but not with the radiative torque intensity. Because of the low dust extinction in our simulation, the magnitude of the radiative torque varies little, decreasing only for column densities larger than 1022 cm−2. In comparing our synthetic maps with those obtained assuming a uniform alignment efficiency, we find no systematic difference and very small random differences. The dependencies of the polarization fraction p with the column density NH or with the dispersion in polarization angle S are also similar in both cases. The drop of grain alignment produced by the RAT model in the denser cells of the data cube does not significantly affect the patterns of the synthetic polarization maps, the polarization signal being dominated by the line-of-sight and beam integration of the geometry of the magnetic field. If a star is artificially inserted at the center of the simulation, the polarization fraction is increased everywhere, with no specific pattern around the star. The angle-dependence of the RAT efficiency is not observed in simulated maps and where the magnetic field is artificially set to a uniform configuration in the plane of the sky, it is only seen to be very weak in the optimal configuration. Conclusions. The RAT alignment theory is found to be compatible with the Planck polarization data for the diffuse and translucent ISM in the sense that both uniform alignment and RAT alignment lead to very similar simulated maps. To further test the predictions of the RAT theory in an environment where an important drop of grain alignment is expected, high-resolution polarization observations of dense regions must be confronted with numerical simulations sampling high-column densities (NH > 1022 cm−2) through dense clouds, given a sufficient statistical basis.

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