CO J = 3-2 observations of the neutral disk in Sagittarius A West

Abstract

Emission has been observed from the J = 3-2 rotational transition of CO over a substantial region in Sgr A West. The mapped region encompasses the dense rotating neutral disk, a structure which extends out to a radius of about 8 pc from the Galactic center. The observations show significant differences from previous CO J = 1-0 observations of Serabyn et al. (1986). In particular, the J = 3-2 emission is more centrally concentrated, and there are differences in the relative strengths of emission peaks in the two sets of maps. The derived picture is one of a disk with a significant excitation gradient, since the emission from high-excitation species declines as one moves out from the center. Typical values of the physical conditions present are density n = 20,000-200,000/cu cm and temperature T = 100-200 K. Antenna temperatures indicate optical depths greater than unity. A CO column density along a line of sight through a clump of roughly 2 x 10 to the 19th/sq cm is inferred.