Cloud Collision–induced Star Formation in Sagittarius B2. I. Large‐Scale Kinematics

Abstract

We present maps of a ∼14 pc × 20 pc region covering the Sgr B2 molecular cloud complex in the 13 CO (1-0) and CS (1-0) lines with high angular resolution. A more restricted central area was also mapped in the C 18 O (1-0) line. The 13 CO cloud consists of two components: a compact core of ∼3 pc in diameter roughly centered on Sgr B2(M) and an extended plateau of ∼17 pc × 7.5 pc area containing the maser sources and most of the H II regions. Compact, massive (∼3 × 10 5 M ⊙ ) C 18 O cores are associated with Sgr B2(M) and Sgr B2(N). The obtained intensity distributions are compared with those of molecular masers and compact H II regions reported in the literature. Low-velocity (40-65 km s -1 ) masers, with positions roughly aligned in the north-south line connecting the three major compact H II region complexes, are located near the eastern margin of a large hole in the low-velocity molecular cloud. In contrast, most of the high-velocity (65-80 km s -1 ) masers are distributed near the center of a compact molecular cloud at higher velocity, where a shock seems to have occurred. These results provide further evidence supporting the cloud-cloud collision hypothesis based on limited 13 CO (1-0) data. In addition, this hypothesis appears to be consistent with a wide range of new observations that have appeared in the literature.