VERY LARGE ARRAY OBSERVATIONS OF THE INFRARED DARK CLOUD G19.30+0.07

We present Very Large Array observations of ammonia (NH3) (1,1), (2,2), and dicarbon sulfide (CCS) (2(1)-1(0)) emission toward the infrared dark cloud (IRDC) G19.30+0.07 at similar to 22 GHz. The NH3 emission closely follows the 8 mu m extinction. The NH3 (1,1) and (2,2) lines provide diagnostics of the temperature and density structure within the IRDC, with typical rotation temperatures of similar to 10-20 K and NH3 column densities of similar to 10(15) cm(-2). The estimated total mass of G19.30+0.07 is similar to 1130M(circle dot). The cloud comprises four compact NH3 clumps of mass similar to 30-160M(circle dot). Two coincide with 24 mu m emission, indicating heating by protostars, and show evidence of outflow in the NH3 emission. We report a water maser associated with a third clump; the fourth clump is apparently starless. A non-detection of 8.4 GHz emission suggests that the IRDC contains no bright H II regions and places a limit on the spectral type of an embedded zero-age main-sequence star to early-B or later. From the NH3 emission, we find that G19.30+0.07 is composed of three distinct velocity components or subclouds. One velocity component contains the two 24 mu m sources and the starless clump, another contains the clump with the water maser, while the third velocity component is diffuse, with no significant high-density peaks. The spatial distribution of NH3 and CCS emission from G19.30+0.07 is highly anti-correlated, with the NH3 predominantly in the high-density clumps and the CCS tracing lower-density envelopes around those clumps. This spatial distribution is consistent with theories of evolution for chemically young low-mass cores, in which CCS has not yet been processed to other species and/or depleted in high-density regions.