Seminar by Tsun Hin Navin Tsung, UCSB
Cosmic ray (CR) protons with energy between 1-300GeV, which dominate the CR population, are believed to be self-confined, i.e. the CRs are scattered by the waves they generate. The end result is that they travel along the magnetic field lines at the local Alfven speed. CRs undergoing this kind of transport are said to be streaming, and in this talk, I will present 'meso-scale' MHD+CR simulations exploring the drastic implications of streaming CRs on gas dynamics in galaxies. First, CR streaming gives rise to a unique feature called 'bottlenecks', where a globally smooth CR pressure profile is shaped into a step-like function in the presence of density bumps, redistributing the energy and momentum transfer from the CRs to the gas. Second, it can drive acoustic waves unstable and give rise to a 'staircase' structure in the CR pressure profile, which can change the mass outflow rate. Third, it alters thermal instability, both in the linear and nonlinear stages. For instance, in the linear state it leads to propagating entropy modes, leading to a new timescale t_alfven that should be considered in addition to t_cool and t_ff for the onset of thermal instability. In the nonlinear stage, as the galactic atmosphere thins out due to thermal instability, CR heating, which is a weaker function of density than radiative cooling, can dominate the energy budget, causing the atmosphere to be overheated and can drive a wind.
Host: Lorenzo Sironi