Statistical TimeDependent Model for the Interstellar Gas
Abstract
We present models for temperature and ionization structure of low, uniformdensity (n 0.3 cm3) interstellar gas in a galactic disk which is exposed to soft Xrays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction x, temperature T, and their various observable moments. These timedependent models predict a bimodal temperature distribution of the gas with structure in x, T that agrees with various observations. Cold regions in the lowdensity gas may have the appearance of clouds in 21cm absorption. The timedependent model, in contrast to the steadystate model, predicts large fluctuations in ionization rate and the existence of cold (T 30 K), ionized (x 0.1) regions. Subject headings: atomic processes interstellar matter  supernovae Xrays
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1974
 DOI:
 10.1086/152768
 Bibcode:
 1974ApJ...189...55G