Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal Conduction - Astrophysics > High Energy Astrophysical PhenomenaReport as inadecuate




Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal Conduction - Astrophysics > High Energy Astrophysical Phenomena - Download this document for free, or read online. Document in PDF available to download.

Abstract: Using a linear stability analysis and two and three-dimensional nonlinearsimulations, we study the physics of buoyancy instabilities in a combinedthermal and relativistic cosmic ray plasma, motivated by the application toclusters of galaxies. We argue that cosmic ray diffusion is likely to be slowcompared to the buoyancy time on large length scales, so that cosmic rays areeffectively adiabatic. If the cosmic ray pressure $p {cr}$ is $\gtrsim 25 %$ ofthe thermal pressure, and the cosmic ray entropy $p { m cr}- ho^{4-3}$;$ ho$ is the thermal plasma density decreases outwards, cosmic rays drive anadiabatic convective instability analogous to Schwarzschild convection instars. Global simulations of galaxy cluster cores show that this instabilitysaturates by reducing the cosmic ray entropy gradient and driving efficientconvection and turbulent mixing. At larger radii in cluster cores, the thermalplasma is unstable to the heat flux-driven buoyancy instability HBI, aconvective instability generated by anisotropic thermal conduction and abackground conductive heat flux. Cosmic-ray driven convection and the HBI maycontribute to redistributing metals produced by Type 1a supernovae in clusters.Our calculations demonstrate that adiabatic simulations of galaxy clusters canartificially suppress the mixing of thermal and relativistic plasma;anisotropic thermal conduction allows more efficient mixing, which maycontribute to cosmic rays being distributed throughout the cluster volume.



Author: P. Sharma, B. D. G. Chandran, E. Quataert, I. J. Parrish

Source: https://arxiv.org/







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