Warm Dense Gas in Luminous Protostellar Regions: A Submillimeter and Far-Infrared CO Line Study

The authors have observed the luminous star formation regions W51 IRS 2, W51 Main, G 34.3+0.1, and W49 in the CO J = 7→6 transition at 372 μm, and W51 IRS 2 and W51 Main in the CO 163 μm J = 16→15 transition. All CO 7→6 spectra show emission from the warm quiescent molecular cloud core. A component of high-velocity emission is apparent in the spectra of W51 IRS 2, W51 Main, and possibly W49. The high-velocity emission from W51 IRS 2 comes from hot (≡10³K), dense (5×10⁴cm^-3) material with a total mass of ≡10²M_sun;. The inferred mass-loss rates in the Galaxy's most luminous star formation regions are at least one order of magnitude larger than in Orion.