Submillimeter Continuum Observations of NGC 7538

Abstract

We present high-resolution millimeter and submillimeter maps (1.3 mm and 850, 800, 450, and 350 μm) of the molecular cloud southeast of 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 connecting to the three major activity centers (IRS 1-3, NGC 7538 S, and IRS 9) in this high-mass star-forming cloud. In addition to the three already known star formation centers, we also find a fainter extended submillimeter source near the 20 μm source IRS 4, at the boundary of the optical H II region. Our high spatial resolution images resolve the young, hypercompact H II region IRS 1 and show that it coincides with a compact (<10'') elliptical dust source with a mass of ≥70 M☉. It is surrounded by a cluster of submillimeter sources, none of which have near- or mid-IR counterparts. Three of the submillimeter sources are associated with H2O masers, suggesting that protostars or young stars have formed in these cloud cores. We find IRS 9 to be an extended elliptical source with a size of 13'' × 6'' at a position angle of -80°, with a second, fainter but more extended source about 20'' south of it. The mass of the IRS 9 submillimeter source is ~150 M☉, while the southern source has a mass of ~90 M☉. The third activity center, NGC 7538 S, is ~80'' south of IRS 1. Here we find a strong, elliptical submillimeter source of 12'' × 7'', with a position angle of 58°. This source coincides with OH and H2O masers and a 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, Td ~ 35 K, has a disklike geometry, drives a very young outflow, and is extremely massive, M ~ 400 M☉. Yet it has a luminosity of only 104 L☉.