THE SAGITTARIUS B2 STAR-FORMING REGION - SUBARCSECOND RADIO SPECTRAL-LINE AND CONTINUUM OBSERVATIONS

We present high-resolution observations of the Sgr B2 region of star formation in the radio continuum at 2 cm and 1.3 cm, at the (J, K) = (3, 2) transition of NH3, and at the 76α hydrogen recombination line. The continuum images show no less than 19 separate H II regions in the Sgr B2 complex. Several H II regions previously believed to be single entities have been resolved into several individual ultracompact H II regions. Four of the H II regions are unresolved, implying an upper limit to their linear size of 0.008 pc. We have detected H76α recombination line emission from one-half of the H II regions detailed in the continuum maps. The large-scale velocity gradient seen in low-resolution thermal molecular observations of the Sgr B2 core is not reflected in the radial velocities of the H II regions as determined by H76α recombination line emission. The H76α recombination line emission from three of the H II regions shows an organized motion of the ionized material within the region. We classify one of these regions as an edge-brightened shell source (Sgr B2 L) and the other two as cometary H II regions (Sgr B2 H and Sgr B2 I). Based on the available data, we suggest that cometary H II regions and expansive shell sources are generally similar in many respects. Both appear to have ionization fronts that are expanding in to the ambient molecular cloud. In addition to general expansion, cometary H II regions appear to be undergoing a champagne flow in one direction. Ammonia emission is observed in the Sgr B2 K and F regions. The emission toward K is found near the K1, K2, and K3 regions. The distribution is not well-fitted by simple rotation or expansion. The NH3 emission and absorption toward the F region, along with the OH maser emission, delineate a rotating disk or torus of molecular material surrounding the Sgr B2 F complex of H II regions. We calculate that the mass interior to the NH3 and OH emission regions must be on the order of 1400 M⊙. We have combined our higher sensitivity, lower resolution ground-state OH main line maser data with those of Gaume and Mutel. We have detected several new maser emission features, most notably in the Sgr B2 K region.