Observational constraints on the multiphase ISM

摘要

In recent years we have seen a wealth of new observations and analysis that sheds light on the distribution and physical properties of various ISM phases. In particular the thermal pressure from C I (Jenkins & Tripp 2011) shows the bulk of the CNM phase with a log normal pressure distribution. It appears that thermal instability is important for phase separation, but with with a thermal pressure variation about the mean driven by turbulence. In additional, there is evidence from C I,H_2,and complex molecules, of both higher and lower pressure environments. An additional "phase" that is of increasing interest for high z,low metallicity galaxies is the C~+ /H_2 gas that is not traced by H I or CO. This review presents the observational evidence for the existence and physical properties of these various ISM phases.