Warm molecular gas associated with cometary Hıı regions

Abstract

We present observations of the (J, K) = (2, 2) and (3, 3) inversion transitions of ammonia, made at ˜4" resolution with the VLA, in the direction of the G32.80 + 0.19 and G61.48 + 0.09 star-forming regions, which contain cometary-like and compact H II regions. Our data reveal the presence, in both complexes, of compact ammonia structures, with sizes of ˜0.2 pc, which are intimately associated with the regions of ionized gas. The ammonia clumps have excitation temperatures in the range 60-80 K and molecular hydrogen densities in the range (0.7-5) × 104 cm-3. We suggest that these warm ammonia clumps correspond to compact molecular structures, embedded within more extended molecular clouds, which have been heated by the radiation from the star that ionizes the associated H II region and possibly compressed by the shocks driven by the expansion of the H II region. We find that the molecular clumps associated with the cometary-like H II regions are located near the head of the ionized region and have line-center velocities similar to those of the ionized gas at the head position. These results imply that the cometary H II regions studied here, which exhibit strong gradients in the line- center velocities along their symmetry axis, are experiencing the champagne phase of evolution. In particular, the case of G6 1.48-0.09 is interesting because it seems that two champagne flows are occurring in this H II region. The ammonia clump associated with the most compact H II region within the G32.80+0.19 complex exhibits the (2, 2) main hyperfine (HF) line in absorption and the (3, 3) main HF line in emission, which we explain as due to a blend, within a synthesized beam, of an emitting region of hot molecular gas and an absorbing region of cold gas in front of a continuum source.