School of Astronomy (SoA) - Weekly Seminar--- Extra session

Study of molecular clouds associated with HII regions

Mohaddesseh Azimlu (University of Western Ontario, Canada)

Abstract:

The properties of molecular clouds associated with 10 H II regions were stud- ied using CO observations. We identified 142 dense clumps within our sample and found that our sources are divided into two categories: those that show a power law size-line width relation (“type I”) and those which do not show any relation (“type II”). The type I sources have larger power law indices than found in previous studies. Type II sources also have larger line widths compared to type I. The MLTE increases with ∆V for both 12CO and 13CO lines in type I sources, no relation was found for type II sources. No relation was found between volume density and size, but overall larger clumps have smaller volume density, indicat- ing that smaller clumps are more evolved and contracted to smaller sizes and higher densities. F Massive clumps seem to have similar masses calculated by different methods but lower mass clumps have larger virial masses compared to velocity integrated (X factor) and LTE mass. We found no relation between mass distribution of the clumps and distance from the HII region ionization front, but a weak decrease of the excitation temperature with increasing distance from the ionized gas.The clumps in collected shells around the H II regions have slightly larger line widths but no relation was found between line width and distance from the H II region, which probably indicates that the internal dynamics of the clumps are not affected by the ionized gas. Internal sources of turbulence, such as outflows and stellar winds from young proto-stars may have a more impor- tant role on the molecular gas dynamics. We suggest that large line width and larger size-line width power law indices are therefore the initial characteristics of massive star forming clouds.

Monday / 27- December-2010 / 6-Dey-1389/ 12:30 PM

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