21 June 2010

Orly Gnat (Caltech)
"NonEquilibrium Ionization Processes in MetalIon Absorbers"
In this talk I will discuss several processes that give rise to
nonequilibrium ionization in metalion absorbers. These include
radiative cooling, fast shock waves, and conductive evaporation of
warm clouds. In each case, I will demonstrate the impact that
departures from equilibrium ionization have on the absorption line
signatures. I will first describe computations of the equilibrium and
nonequilibrium ionization states and cooling efficiencies in
radiatively cooling gas. I will then discuss models of the
nonequilibrium cooling column densities associated with fast
radiative shocks, including the effect of the shock selfradiation on
the "downstream" ionization states. In these models I
selfconsistently follow the timedependent dynamics, ionization,
cooling and radiative transfer equations in one dimensional stable
shocks. I will describe how the observational signatures depend on the
controlling parameters, including the shock velocity, gas metallicity,
magnetic field, and shock age. Finally, I will present recent
computations of thermally conductive interface layers, that may
surround evaporating clouds embedded in a hot medium. These models
include photoionization by an external radiation field. I will
describe how departures from equilibrium affect the conditions for
which selfconsistent evaporating solutions exist, and the metalion
columns produced in the evaporating layers.
