Molecular Clouds Under Pressure Alyssa Goodman Harvard-Smithsonian Center for Astrophysics, Cambridge, USA
Two vexing questions in star formation research are: 1) what is a "cloud"?; and 2) what is the role of pressure-confinement, especially as compared with gravity, in the evolution of star-forming clouds? In this work we show the first results of a new attempt to address these two questions simultaneously. By de-composing the entire Dame et al. 2001 CO Survey of the Milky Way into a hierarchical catalog of nested "clouds," we can study the pressure structure as a function of scale within the molecular interstellar medium. We accomplish this by: 1) constructing a "dendrogram" (tree-hierarchy) decomposition of CO emission in 3D (position-position-velocity) space; and then 2.) analyzing the features (akin to surfaces) in the dendrogram to estimate how "bound" either by gravity or by pressure the features appear to be. The dendrogram decomposition is very insensitive to noise and parameter settings, so our results offer unbiased new catalogs of "clouds" defined by their apparent gravitational and pressure-related properties. We compare catalogs of "self-gravitating" vs. "pressure-bound" clouds, noting remarkable differences. By comparing extant catalog of star-forming regions and star-formation indicators (e.g. HII regions) into the context of these new catalogs, we can determine whether pressure is a good determinant of the star-forming potential of molecular gas within our Galaxy, and whether pressure structure is more or less useful as a measure than "self-gravity" as measured by the standard virial parameter.
Collaborators: T. Rice, Harvard, USA J. Alves, U. Vienna, Austria B. Benjamin, CfA, USA C. Beaumont, CfA, USA T. Dame, CfA, USA C. Faesi, CfA, USA M. Reid, CfA, USA E. Rosolowsky, UBC Okanagan, Canada