2011ApJ...728....6Q

We present a Submillimeter Array study in the 1.3 mm wave band of the NGC 7538 IRS 1-3 massive star-forming region. The brightest core in the millimeter continuum map, MM1, harbors the IRS 1 young O star. The core has a gas temperature of about 245 K and shows spatially unresolved emission in complex organic molecules, all typical of a hot molecular core. Toward MM1, redshifted absorption is seen in molecular lines with different energies above the ground state. This absorption probes the inward motion of the dense gas toward the central young O star, and the estimated mass accretion rate reaches 10^–3 M_☉/yr. Multiple outflows are seen in the CO and ¹³CO maps. The gas mass of 50 M_☉ and the mass outflow rate of 2.5x10^–3 M_☉/yr measured in CO line wings are dominated by the MM1 outflow, which is most likely driven by a fast wide-angle wind. Apart from MM1, we discover eight new dusty cores, MM2-9, within a projected distance of 0.35 pc from MM1. These cores show no counterpart in infrared or radio continuum emission, while seven of them appear to be forming intermediate- to high-mass stars. This manifests a deeply embedded star-forming component of the parent cloud of IRS 1-3. Apparently, we are observing a Trapezium system in formation, and the system is presumably surrounded by a cluster of lower mass stars.