AAS 207th Meeting, 8-12 January 2006
Session 119 The Dirty Side of the ISM - Theory and Dust
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

## [119.06] Detailed microphysics of H0 and its effect on the 21 cm spin temperature

G. Shaw, G. Ferland (University of Kentucky), R. Srianand (IUCAA)

The kinetic temperature of a gas in different interstellar environments is often inferred from the level populations assuming thermal equilibrium and the Boltzmann equation. In general it is believed that the 21 cm spin temperature usually traces the kinetic temperature. Temperature can also be determined from the integrated optical depth ratio of the Ly\alpha and 21 cm lines. Here we present a number of numerical simulations of environments where these temperature indicators are used, with a detailed treatment of the physical processes that determine level populations within H0. This includes detailed Lyman line transfer and the effects of cosmic ray excitation and continuum pumping. We demonstrate situations where these temperature indicators fail to trace the kinetic temperature, as well as the effects of Ly\alpha on the 21 cm spin temperature.

Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.