The NGC 7538 IRS 1 region of star formation: Observations of the H66 alpha recombination line with a spatial resolution of 300 AU

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Abstract

The 1.3 cm continuum and the H66 alpha recombination line emission toward NGC 7538 IRS 1 have been imaged with a spatial resolution of 180 and 300 AU, respectively. There are several remarkable aspects to the data. The core of the H II region is composed of numerous emission clumps with peak brightness temperatures of approximately equals 15,000 K. Extremely wide line profiles, 250 km/s FWZP, are observed from the core; indicating substantial mass motions of the ionized gas. The H66 alpha spectral profiles exhibit multiple emission peaks. The peaks and shapes of the H66 alpha recombination line profiles vary significantly as a function of position within the core region. The H66 alpha line-to-continuum ratios also vary considerably within the core region. A thin strip midway between the northern and southern core continuum components is the region of largest electron density. The center of this dense, disk-like structure most likely delineates the position of the exciting star. We present a model for NGC 7358 IRS 1 that involves a stellar wind outflow and photoevaporation of nearby clumpy neutral material. This results in a clumpy continuum appearance and a complicated set of broad- and multiple-peaked spectral profiles. Ionized gas escapes the core region in an outflow to the north and south. Toward the south the outflow is partially limited by neutral material, producing a southern, spherical continuum component which exhibits much narrower H66 alpha line profiles than the core region.

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