Submillimeter Continuum Observations of NGC 7538

Abstract

We present high-resolution millimeter and submillimeter maps (1.3mm and 850, 800, 450, and 350 mum) of the molecular cloud southeastof NGC 7538, obtained on the IRAM 30 m telescope at Pico Veleta,Spain and the 15 m James Clerk Maxwell Telescope on Mauna Kea, Hawaii.These maps show filamentary dust ridges extending from and connectingto the three major activity centers (IRS 1 - 3, NGC 7538 S, and IRS9) in this high-mass star - forming cloud. In addition to the threealready known star formation centers, we also find a fainter extendedsubmillimeter source near the 20 mum source IRS 4, at the boundaryof the optical H II region. Our high spatial resolution images resolvethe young, hypercompact H II region IRS 1 and show that it coincideswith a compact (<10&DPRIME;) elliptical dust source with a massof &GE;70 M-.. It is surrounded by a cluster of submillimeter sources,none of which have near- or mid-IR counterparts. Three of the submillimetersources are associated with H2O masers, suggesting that protostarsor young stars have formed in these cloud cores. We find IRS 9 tobe an extended elliptical source with a size of 13&DPRIME; x 6&DPRIME;at a position angle of -80&DEG;, with a second, fainter but moreextended source about 20&DPRIME; south of it. The mass of the IRS9 submillimeter source is &SIM; 150 M-., while the southern sourcehas a mass of &SIM; 90 M-.. The third activity center, NGC 7538S, is &SIM; 80&DPRIME; south of IRS 1. Here we find a strong, ellipticalsubmillimeter source of 12&DPRIME; x 7&DPRIME;, with a positionangle of 58&DEG;. This source coincides with OH and H2O masers anda faint VLA 6 cm source, but it shows no near- or mid-infrared emission.We find NGC 7538 S to have all the characteristics of a Class 0 source;i.e., it is a high-mass protostar. It is cold, T-d &SIM; 35 K, hasa disklike geometry, drives a very young outflow, and is extremelymassive, M &SIM; 400 M-.. Yet it has a luminosity of only 10(4)L-..