High Velocity Gas Flows Associated with h2 Emission Regions - how are they Related and what Powers Them

Abstract

We report on an investigation of high-velocity molecular material near the vibrationally excited H<SUB>2</SUB> emission regions in the objects DR 21, W75 N, NGC 7538, OMC-2, NGC 6334/Peak V, and the Herbig-Haro Object 2. The <SUP>12</SUP>CO(J = 1-0) and <SUP>13</SUP>CO(J = 1-0) transitions were used as tracers of the high-velocity molecular flows. All the H<SUB>2</SUB> sources are associated with bipolar CO high-velocity flows. We also present a new highspatial-resolution map (11") of the DR 21 H<SUB>2</SUB> region. The spatial relationship of the high-velocity gas and the vibrationally excited gas, together with the similarity of the energies involved in the two molecular components, is convincing evidence to support the scenario in which the H<SUB>2</SUB> emission traces the cooling gas that has been shocked by outflowing gas. Although radiation pressure could be responsible for driving the flows in OMC-2 and NGC 7538, it is unlikely to be the driving mechanism in DR 21 and W75 N. Similarly, H II region expansion does not appear to be the driving mechanism for any of the outflows.