Spatial distributions and kinematics of shocked and ionized gas in M17

Abstract

ABSTRACTMassive stars are formed in molecular clouds, and produce H ii regions when they evolve onto the main sequence. The expansion of H ii region can both suppress and promote star formation in the vicinity. M17 H ii region is a giant cometary H ii region near many massive clumps containing starless and protostellar sources. It is an appropriate target to study the effect of feedback from previously formed massive stars on the nearby star-forming environments. Observations of SiO 2-1, HCO+ 1-0, H13CO+ 1-0, HC3N 10-9, and H41 α lines are performed toward M17 H ii region with ambient candidates of massive clumps. In the observations, the widespread shocked gas surrounding M17 H ii region is detected: it probably originates from the collision between the expanding ionized gas and the ambient neutral medium. Some massive clumps are found in the overlap region of the shock and dense-gas tracing lines while the central velocities of shocked and high-density gases are similar. This suggests that part of massive clumps are located in the shell of H ii region, and may be formed from the accumulated neutral materials in the shell. In addition, by comparing the observations towards M17 H ii region with the simulation of cometary H ii region, we infer the presence of one or more massive stars travelling at supersonic velocity with respect to the natal molecular cloud in the H ii region.