Speaker
Jouni Kainulainen
(Max-Planck-Institute for Astronomy)
Description
Supersonic turbulence has a profound impact on the density structure of the cold interstellar medium (ISM). Consequently, observations of the ISM density structure can be used to constrain the fundamental properties of turbulence. However in practice, connecting the observed density structure to theoretical predictions is greatly hampered by the inability of observations to probe the wide range of (column) densities present in the ISM. In this contribution, I present our recent observational works in which we analyze the density statistics of molecular clouds using a new dust extinction mapping technique that allows us to probe the clouds, in a uniformly calibrated manner, over a wide dynamic range of column densities. We employ the technique to study the column density probability distribution functions (PDFs) of molecular clouds and their relation to the turbulence energy in the clouds. Our results show that the molecular cloud PDFs correlate strongly with star-forming activity, and also strongly with the Galactic environment. In particular, clouds located in spiral arm regions contain considerably more high-column density gas than those in the Solar neighborhood. We analyze a set of numerical turbulence simulations to understand the origin of this trend. We show that one potential explanation for the high amount of dense gas in spiral arm clouds is provided by more compressive gas motions in those regions. Finally, we use our high-dynamic range column density data to constrain the correlation coefficient (b) between density variance and turbulence energy in molecular clouds. Our results suggest that b can vary between clouds depending on their large-scale, Galactic environment.
Author
Jouni Kainulainen
(Max-Planck-Institute for Astronomy)