On the intrinsic shape of molecular clouds

Abstract

\n Knowledge of the intrinsic shape of molecular clouds and molecular\ncloud cores provides useful information on both the formation and\ncollapse mechanisms associated with the objects and on the initial\nconditions for star formation. We compare the\nshapes of molecular clouds as determined by \nthe [CITE][ HCS01]hcs01 and [CITE][ BKP03]bkp03 catalogues of\n12CO($J=1-0$) emission in the outer Galaxy. The catalogues are\nbased upon different versions of the FCRAO Outer Galaxy Survey and also utilize\ndifferent techniques for defining both the extent and shape of the\nclouds, which allows us to examine the effects of using different cloud \ndefinition and shape-fitting algorithms. In order to compare the two \ncatalogues we use a subset of the cloud population where the clouds\nare well-defined in both data sets. We model the clouds\nin terms of triaxial ellipsoids and use a Monte Carlo technique to\ndetermine the best-fit intrinsic shape distribution which matches the\nobserved axis ratio distributions. Our analysis shows that the\nobserved shapes of molecular clouds can be best described in terms of\nan intrinsic distribution of triaxial ellipsoids that are intermediate\nbetween near-oblate and near-prolate ellipsoids. The lack of high axis\nratio clouds seen in the HCS01 catalogue is shown to be an artifact of\nthe cloud definition algorithm and not an intrinsic property of the\nmolecular clouds. \n\n \n