 |
|
| EPoS Contribution |
|
Mass-Size Studies of Regions of low-mass and high-mass Star Formation
Jens Kauffmann Jet Propulsion Laboratory, Pasadena, USA | |
| One of the most fundamental properties of molecular clouds are their masses, m, and sizes (e.g., radius, r). In the early 1980's, it was suggested that all clouds follow m(r) = 460 M_sun (r / pc)^1.9. This relation was, however, only designed to describe cloud properties to an accuracy of an order of magnitude. Today, dust emission and extinction data permit to comprehensively explore the physics underlying the "scatter" in the mass-size data. This yields updated versions of mass-size laws. Based on a new method to characterize mass-size structure in clouds, we show that no single mass-size law can describe all aspects of cloud structure. In a sample of solar-neighborhood clouds not forming massive stars, all cloud fragments are found to have a mass smaller m_lim(r) = 870 M_sun (r / pc)^1.33. In contrast to this, all our sample clouds forming massive stars do exceed this limit. This excess is not surprising on the spatial scale of actual star formation (<0.1 pc). However, we show that these excesses also prevail at large radii (>10 pc). This research thus uniquely quantifies the impact of large-scale cloud structure on the star formation activity at small spatial scales. Finally, we use our mass-size studies of solar neighborhood clouds as a tool to characterize distant Infrared Dark Clouds (IRDCs). This permits for the first time to compare local and distant clouds at the same physical scale. Specifically, we compare published mass-size observations to our aforementioned mass-size limit for solar neighborhood clouds not forming massive stars. This shows that many IRDCs have a structure consistent with solar neighborhood clouds. In particular, in two IRDC samples selected to only contain unusually dense objects (i.e., high contrast in 8 micron images), the fraction of clouds more massive than solar neighborhood clouds not forming massive stars is <1/3. These results call for a re-evaluation of IRDCs as a pool of regions of high mass star formation: just a small fraction of the ~11000 IRDCs presently known is structurally different from Perseus, Ophiuchus, and Taurus. | |
 | |
| Caption: Mass-size data for solar neighborhood clouds not forming massive stars (top), high mass protostellar objects (middle), and IRDCs (bottom). In all panels, the limiting mass-size relation for solar neighborhood clouds not forming massive stars is drawn. Many unusually dense IRDCs fall short of the mass limit. These extreme IRDCs seem to be structurally similar to solar neighborhood clouds like Perseus, Ophiuchus, Taurus, and the Pipe Nebula. | |
| Collaborators: T. Pillai, Caltech, USA R. Shetty, ZAH, Germany P.C. Myers, HSCfA, USA A.A. Goodman, HSCfA, USA |
Key publication
Suggested Session: Cores and Collapse, Massive Stars, Molecular Clouds |