High‐Mass Protostellar Candidates. II. Density Structure from Dust Continuum and CS Emission

We present a detailed 1.2 mm continuum and CS spectral line study of a largesample of 69 massive star forming regions in very early stages of evolution,most of them prior to building up an ultracompact HII region. The continuumdata show a zoo of different morphologies and give detailed information on thespatial distributions, the masses, column densities and average densities ofthe whole sample. Fitting the radial intensity profiles shows that threeparameters are needed to describe the spatial distribution of the sources:constant emission from the center out to a few arcsec radius followed by afirst power law intensity distribution which steepens further outside into asecond power law distribution. The mean inner power law intensity index mi(I~r^(-mi)) is 1.2 corresponding to density indices p (n~r^(-p)) of 1.6. Intotal the density distribution of our massive star formations sites seem to benot too different from their low-mass counterparts, but we show that settingtight constrains on the density indices is very difficult and subject to manypossible errors. The local densities we derive from CS calculations are higher(up to one order of magnitude) than the mean densities we find via themm-continuum. Such inhomogeneous density distribution reflects most likely theubiquitous phenomenon of clumping and fragmentation in molecular clouds.Linewidth-mass relations show a departure from virial equilibrium in the stagesof strongly collapsing cores.Comment: 15 pages, 13 jpeg-figures. Astrophysical Journal, in pres