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Nordita Astrophysics seminars

Diffuse neutral interstellar medium: temperature and turbulence

by Nirupam Roy (Indian Institute of Science)

The thermal steady state model was the basis of our theoretical understanding of the temperature of the diffuse atomic interstellar medium. However, recently there have been strong indications of the existence of a large fraction of gas in the intermediate temperature unstable state. Naturally, this has raised serious doubts about the validity of the thermal equilibrium model. In this talk, I will discuss physical conditions in Galactic neutral hydrogen based on deep, high velocity resolution interferometric HI 21 cm absorption spectroscopy. In this context, I will also discuss, from an observer's point of view, the need of characterizing the nature of the interstellar turbulence to constrain the temperature of the diffuse neutral interstellar medium. Correctly accounting for the turbulence in the interstellar medium is important to firmly establish that a significant fraction of the gas in the Galactic interstellar medium has temperatures outside the ranges expected for thermally stable gas in two-phase models.