The Temperature Distribution in Turbulent Interstellar Gas

Abstract

We discuss the temperature distribution in a two-dimensional, thermally unstable numerical simulation of the warm and cold gas in the Galactic disk, including the magnetic field, self-gravity, the Coriolis force, stellar energy injection, and a realistic cooling function. We find that ~50% of the turbulent gas mass has temperatures in what would be the thermally unstable range if thermal instability were to be considered alone. This appears to be a consequence of there being many other forces at play than just thermal pressure, constituting a different process from that proposed in time-dependent models based on stochastic heating followed by cooling, although the latter mechanism may also be present. We also point out that a bimodal temperature probability distribution function is a simple consequence of the form of the interstellar cooling function and is not necessarily a signature of discontinuous phase transitions.