The Sagittarius B2 Star-forming Region. I. Sensitive 1.3 Centimeter Continuum Observations

Abstract

The radio continuum toward the Sgr B2 region of star formation has been imaged at a wavelength of 1.3 cm with a spatial resolution of ≍2000 AU (0".25) and a sensitivity of ≍0.4 mJy beam-1. These high-quality images show many newly detected continuum components and reveal remarkable features associated with several previously known H II regions. Current models of ultracompact H II regions are discussed within the context of these new data. The images detail 49 individual continuum components within the Sgr B2 complex. Half of these have diameters less than 5000 AU, including several unresolved components (diameters <2100 AU). These H II regions may be explained by a disk photoevaporation model. There are many asymmetrically bright shell-like and arclike H II regions in Sgr B2. The asymmetries observed in the 1.3 cm continuum from these shell-like and arclike H II regions correspond to gradients in the 20 cm → 1.3 cm spectral indices, reflecting gradients in the electron densities within many of these H II regions. These shell- and arclike sources may be best described by an "improved" champagne flow model, incorporating stellar winds and significant gradients in the density of ambient neutral material. Numerous filamentary structures are seen in images of the long-tail cometary H II region Sgr B2 I. At least three components are identified in the tail region exhibiting two different position angles on the plane of the sky. The morphology may result from an interaction between the ionized gas of Sgr B2 I and external winds which originate within the nearby Sgr B2 F cluster of H II regions.

The Sagittarius B2 Star-forming Region. I. Sensitive 1.3 Centimeter Continuum Observations

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