We present observations of the W51 high-mass star-forming region at 86 and 110 GHz made with the Berkeley-Illinois-Maryland Association (BIMA) array. The observations include the H~(13)CO~+(J = 1 → 0), SiO(J = 2 → 1, v = 0), SO_2(8_(1,7) → 8_(0,8)), SO_2(8_(3,5) → 9_(2,8_), ~(13)CO(J = 1 → 0), and C~(18)O(J = 1 → 0) lines. We compare the H~(13)CO~+(J = 1 → 0) data to earlier work and find that these data support the hypothesis that infall in the W51 region is taking place in several localized regions, each involving on the order of 100 solar mass of gas. The data do not support the hypothesis that the collapse is global, involving tens of thousands solar mass of gas. We calculate dust masses for two dense cores containing ultra-compact H Ⅱ regions and find that these masses are consistent with the localized infall model, being on the order of 100 solar mass. We estimate gas column densities from the observations of CO and SO_2 and find them to be consistent with the other mass estimates, assuming abundances from other hot molecular cores.
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