Sub-arcsec Observations of NGC 7538 IRS 1: Continuum Distribution and Dynamics of Molecular Gas


We report new results based on the analysis of the SMA and CARMA observations of NGC 7538\,IRS\,1 at 1.3 and 3.4 mm with sub-arcsec resolutions. With angular resolutions \sim 0\farcs7, the SMA and CARMA observations show that the continuum emission at 1.3 and 3.4 mm from the hyper-compact \ion{H}{2} region IRS\,1 is dominated by a compact source with a tail-like extended structure to the southwest of IRS\,1. With a CARMA B-array image at 1.3 mm convolved to 0\farcs1, we resolve the hyper-compact \ion{H}{2} region into two components: an unresolved hyper-compact core, and a north-south extension with linear sizes of <270<270 AU and \sim2000 AU, respectively. The fine structure observed with CARMA is in good agreement with the previous VLA results at centimeter wavelengths, suggesting that the hyper-compact \ion{H}{2} region at the center of IRS\,1 is associated with an ionized bipolar outflow. We image the molecular lines OCS(19-18) and CH3_3CN(12-11) as well as 13^{13}CO(2-1) surrounding IRS\,1, showing a velocity gradient along the southwest-northeast direction. The spectral line profiles in 13^{13}CO(2-1), CO(2-1), and HCN(1-0) observed toward IRS\,1 show broad redshifted absorption, providing evidence for gas infall with rates in the range of 310×1033-10\times10^{-3} M_\odot yr1^{-1} inferred from our observations.Comment: 19 pages, 14 figure

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