Outflows, Accretion, and Clustered Protostellar Cores around a Forming O Star

TL;DR

This study uses submillimeter observations to analyze the complex gas dynamics, outflows, and multiple protostellar cores around a forming O star in NGC 7538, revealing a clustered star formation environment.

Contribution

First detailed submillimeter study of the NGC 7538 IRS 1--3 region revealing multiple protostellar cores and their associated outflows around a forming O star.

Findings

Detection of inward gas motion toward the O star with high accretion rate.

Identification of multiple outflows driven by the central core.

Discovery of eight new dusty cores indicating clustered star formation.

Abstract

We present a Submillimeter Array study in the 1.3 mm waveband of the NGC 7538 IRS 1--3 massive star-forming region. The brightest core in the mm 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 inward motion of the dense gas toward the central young O star, and the estimated mass accretion rate reaches 10^{-3} Msun/yr. Multiple outflows are seen in the CO and 13CO maps. The gas mass of 50 Msun and mass outflow rate of 2.5 by 10^{-3} Msun/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.