Diffuse Neutral Interstellar Medium : Results from HI studies

Séminaire IPAG de Nirupam Roy (MPI Bonn), jeudi 2 avril 2015 à 11h00, IPAG seminar room

The interstellar medium is known to have significant density and velocity structures over a wide range of spatial scales. These structures are generally interpreted as the signature of turbulence in the interstellar medium. Radio astronomical observations are particularly useful to study two closely related aspects, the turbulence and the multiphase nature, of the interstellar gas. In this presentation, I will summarize some recent results from various observations, probing the interstellar medium turbulence from parsec to AU scale using several complimentary techniques. In this context, I will 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. I will also present results from an ongoing neutral hydrogen absorption study. Correctly estimating the temperature of the turbulent multiphase interstellar medium is an important issue, particularly in light of recent results from this study, that a significant fraction of the gas is in the thermally unstable phase, and that the standard two-phase thermal steady state models may not be entirely correct.