VLA Spectral Line Observations of a Shocked Cold H II Region in G70.7+1.2
Abstract
We have observed the molecular globule G70.7+1.2 at 1375 MHz using the C configuration of the VLA, and have imaged a peculiar H168 alpha recombination line detected at the Arecibo radio telescope. The narrow width of the recombination line ( Delta v ~ 3 km s-1) indicates gas cooler than 185 K and suggests that the globule harbors the coldest known H II region. Previous work showed that the recombination line came either from newly ionized gas outside a bow shock produced by supersonic motion of an early-type star through the molecular globule, or from a cold H II region inside the globule. The 20" angular resolution of the VLA image of G70.7+1.2 was sufficient to resolve the separation between the nonthermal radio-emitting bow shock and the thermal H II region. The spectral line images show that the radio recombination line comes from cold gas near the outer boundary of the bow shock and that the line intensity is enhanced by stimulated amplification of the nonthermal continuum emanating from the bow shock.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 1995
- DOI:
- 10.1086/309645
- Bibcode:
- 1995ApJ...449L.127O
- Keywords:
-
- ISM: H II REGIONS;
- RADIO LINES: ISM