Sagittarius B2 main: A cluster of ultra-compact h II regions and massive protostellar cores

Abstract

The ionized core in the Sgr B2 Main star-forming region was imaged using the Submillimeter Array archival data observed for the H26α line and continuum emission at 0.86 mm with an angular resolution 03. Eight hyper-compact H26α emission sources were detected with a typical size in the range of 1.6-20 × 102 AU and electron density of 0.3-3 × 10 7cm-3, corresponding to the emission measure 0.4-8.4 × 1010cm-6 pc. The H26α line fluxes from the eight hyper-compact H II sources imply that the ionization for each of the sources must be powered by a Lyman continuum flux from an O star or a cluster of B stars. The most luminous H26α source among the eight detected sources requires an O6 star that appears to be embedded in the ultra-compact H II region F3. In addition, ∼23 compact continuum emission sources were also detected within the central 5″× 3″(∼0.2 pc) region. Under the assumption of a power-law distribution for the dust temperature, with the observed brightness temperature of the dust emission we determined the physical properties of the submillimeter emission sources, showing that the molecular densities are in the range of 1-10 × 108cm-3, surface densities between 13 and 150 gcm-2, and total gas masses in the range from 5 to ≳ 200 M Ȯ, which are one or two orders of magnitude greater than the corresponding values of the Bonnor-Ebert mass. With a mean free-fall timescale of 2 × 103 years, each of the massive protostellar cores is undergoing gravitational collapse to form new massive stars in the Sgr B2 Main core. © 2011. The American Astronomical Society. All rights reserved..