THE SAGITTARIUS B2 STAR-FORMING REGION. II. HIGH-RESOLUTION H66α OBSERVATIONS OF SAGITTARIUS B2 NORTH

摘要

We have observed the Sagittarius B2 (Sgr B2) North star-forming region with the Very Large Array in the continuum (1.3 cm) and in the radio recombination lines H66α and He66α. Sgr B2 North contains regions of ionized gas ranging in size from unresolved (d < 0.01 pc) to extended (d ～ 0.5 pc) and thus presents an ideal laboratory to study the effects of circumstellar environments on H II region evolution. The H66α data provide high spatial (0.25″) and spectral (10 km s~(-1)) resolution kinematics of the ionized gas associated with massive stars. The helium and hydrogen data are used together as a high-resolution probe of Y~+ values and variations within Sgr B2. In Sgr B2 North, we measure a helium abundance of < Y~+ > = 13% ± 2%. We present the H66α and He66α results from Sgr B2 K, and the nearby sources L, R, and X. Region K consists of six sub-regions, one of which (K6) has a continuum morphology and a double-peaked spectral line consistent with an expanding shell of ionized gas (v(_exp) ～ 22 km s~(-1)). We detect no radio recombination line emission (T_lT_C < 3%) from the ultracompact H n region K2, which is cospatial in projection with the dynamical center of a bipolar molecular outflow imaged in HC_3N (Lis et al. 1993). The recombination line velocities of K1 and K3 agree with the north-south rotation in molecular gas observed by Lis et al. (1993). Source L is an "arclike" region with a large velocity gradient of ～70 km s~(-1) pc~(-1) perpendicular to its edge-brightened rim. The large velocity gradient at this orientation observed in Sgr B2 L may be due to rotation of the ionized gas around ～ 150-200 solar mass, consisting of low-mass stars.