Ammonia absorption toward NGC 7538 IRS 1 - 2 arcsecond observations in the (3,3) line

Abstract

Absorption from the (3, 3) line of NH<SUB>3</SUB> has been detected at -60.0 km s<SUP>-1</SUP> toward the ultracompact H II region IRS 1 in NGC 7538 with the VLA. In single-dish spectra, the line is blended with an emission component at -56.5 km s<SUP>-1</SUP>. With the 2arcsec.5×2arcsec.2 beam, however, line emission is resolved. This corresponds to a spatial extent of more than 10arcsec. The molecular cloud covers at least 60% of the continuum source; this is approximately 1arcsec, corresponding to 0.017 pc. From the line shape, the cloud may consist of several clumps of size less than 0.01 pc, each with a different radial velocity and smaller line width. In addition to the spectral line measurements, a 23.87 GHz continuum map of IRS 1, 2, 3 is presented.