The Molecular Clouds Associated with the H ii Regions/Candidates between L = 207.°7 and L = 211.°7

Abstract

Using the PMO-13.7 m millimeter telescope at Delingha in China, we have conducted a large-scale simultaneous survey of 12 CO, 13 CO, and C 18 O J  = 1 − 0 emission toward the sky region centered at l  = 209.°7, b  = −2.°25 with a coverage of 4.°0 × 4.°5. The majority of the emission in the region comes from the clouds with velocities lying in the range from −3 to 55 km s −1 , at kinematic distances from 0.5 to 7.0 kpc. The molecular clouds in the region are concentrated into three velocity ranges. The molecular clouds associated with the 10 H ii regions/candidates are identified and their physical properties are presented. Massive stars are found within Sh2-280, Sh2-282, Sh2-283, and BFS54, and we suggest them to be the candidate excitation sources of the H ii regions. The distributions of the excitation temperature and line width with the projected distance from the center of H ii region/candidate suggest that the majority of the 10 H ii regions/candidates and their associated molecular gas are three-dimensional structures, rather than two-dimensional structures.