Ionized Gas in Sagittarius B2 Main on Scales of 0.065 Arcsecond (600 AU)

Abstract

The ionized gas in the Sagittarius B2 Main star-forming region has been imaged with ~65 mas (600 AU) resolution using the Very Large Array (VLA) at 7 mm in the A configuration. These observations have ~4-5 times the resolution of the previous highest resolution images of this source. These VLA observations show that the central four ultracompact H II (UC H II) regions in Sgr B2 Main (F1, F2, F3, and F4) break up into ~20 separate UC H II regions. The individual sources have small resolved sizes (~10-3 pc), high derived emission measures (EM ~ 109 pc cm-6), and high rms electron densities (ne ~ 106 cm-3). We compare the observed radius and derived emission measure of each of these regions with those expected for a UC H II region in pressure equilibrium with its environment, using previously published temperatures and densities for the Sgr B2 molecular core (nH2=2×107 cm-3). We find that the observed emission measures are in fact higher than those predicted in a simple pressure-confinement model, suggesting that the molecular densities on scales that confine the UC H II regions may be higher than 2 × 107 cm-3.