Dynamical Collapse in W51 Massive Cores: CS (3–2) and CH₃CN Observations

Abstract

We present interferometric observations of the W51 region at 2 mm with the Nobeyama Millimeter Array. The 320 MHz band centered at 147 GHz covers transitions of the CS (3-2), CH3CN (8-7), H35α, CH3OCH3 (7-6) and (6-6), and HCOOCH3 (12-11), as well as the 2 mm continuum. Toward two dense cores, W51e2 and W51e8, spectroscopic signatures of cloud collapse are present in all the molecular lines observed. Line asymmetries increase systematically toward transitions of larger optical depths, consistent with expected signatures of a centrally condensed infalling cloud. Furthermore, the disparity between the blueshifted and the redshifted emission of the CS line is enhanced when the line is synthesized at higher angular resolution. Given that the continuum source is embedded in the core, we are able to locate the emitting gas of the blueshifted emission on the rear side and the gas of the redshifted emission on the front side of the central star. The new observations confirm our infall interpretations regarding the e2 and e8 cores based on the NH3 data.