Invited Talk - Plenary

Thursday, 14 September 2023, 11:30   (H 0104 / virtual plenum)

Numerical Simulations of the Dynamical and Ionic Evolution of the Interstellar Medium

Miguel A. de Avillez
University of Evora, PT

The majority of the published two- and three-dimensional simulations of the interstellar gas, including the disk-halo interaction, are set up under the assumption of collisional ionization equilibrium (CIE). However, even disregarding the dynamics of the medium the rates of collisional ionization and radiative recombination do not balance, so that as time goes by the ionization structure is severely driven out of equilibrium. Consequently, the cooling rates and the gamma parameter vary as a function of time. Taking into account the dynamics of the plasma, the imbalance becomes even more severe, because adiabatic compression or expansion can change the kinetic temperature of the electrons significantly, while leaving the ionization structure at first unchanged. Hence, ionization and recombination can be delayed. It is important to realize that the dynamical and thermal history of the plasma are inextricably intertwined.
An adequate picture of the interstellar medium requires numerical simulations taking into account the joint dynamical (HD or MHD) and thermal (tracing the ionic structure and the corresponding emissivities) evolution of the gas in a self-consistent way. A review of the current state of these models is presented.