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تسجيل مستخدم جديدThe Galactic Census of High- and Medium-mass Protostars. III $^{12}$CO Maps and Physical Properties of Dense Clump Envelopes and their Embedding GMCs
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Peter J. Barnes
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We report the second complete molecular line data release from the {em Census of High- and Medium-mass Protostars} (CHaMP), a large-scale, unbiased, uniform mapping survey at sub-parsec resolution, of mm-wave line emission from 303 massive, dense molecular clumps in the Milky Way. This release is for all $^{12}$CO $J$=1$rightarrow$0 emission associated with the dense gas, the first from Phase II of the survey, which includes $^{12}$CO, $^{13}$CO, and C$^{18}$O. The observed clump emission traced by both $^{12}$CO and HCO$^+$ (from Phase I) shows very similar morphology, indicating that, for dense molecular clouds and complexes of all sizes, parsec-scale clumps contain $Xi$ ~ 75% of the mass, while only 25% of the mass lies in extended (>~ 10 pc) or low density components in these same areas. The mass fraction of all gas above a density 10$^9$ m$^{-3}$ is $xi_9$ >~ 50%. This suggests that parsec-scale clumps may be the basic building blocks of the molecular ISM, rather than the standard GMC concept. Using $^{12}$CO emission, we derive physical properties of these clumps in their entirety, and compare them to properties from HCO$^+$, tracing their denser interiors. We compare the standard X-factor converting $I_{CO}$ to $N_{H_2}$ with alternative
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