High-velocity OH in absorption - A new tracer of shocked gas in outflows?

Details High-velocity OH in absorption - A new tracer of shocked gas in outflows? High-velocity OH in absorption - A new tracer of shocked gas in outflows?

Oct 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...398..139r&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 398, no. 1, p. 139-145.

Astronomy and Astrophysics

Astronomy

7

Absorption Spectra, Gas Flow, Hydroxyl Emission, Radio Sources (Astronomy), Star Formation, Hydrogen, Line Spectra, Molecular Excitation, Shock Waves, Very Large Array (Vla)

Scientific paper

We report VLA observations of the 1667 MHz transition of OH and of the adjacent continuum toward the galactic star-forming regions NGC 2071 and S255. In NGC 2071 we mapped bipolar, high-velocity OH in absorption and compared its morphology with that of the CO and H2 bipolar outflows previously detected in the region. The maxima of high-velocity OH absorption appear to correlate better with the maxima of the H2 emission, and we suggest that the OH may trace shocked gas. The high-velocity OH appears in absorption against the cosmic background plus a small Galactic contribution, and we conclude that the OH excitation temperature is anomalously low. Using new rates for the collisions between OH and H2, we have been able to model these anomalously low excitation temperatures for gas with kinetic temperature 50 K and density of molecular hydrogen in the range of 10 exp 2 - 10 exp 9/cu cm. In the case of S255 we detected high-velocity (about 50 km/s) blueshifted OH in absorption. This gas appears projected against the compact H II region G192.58 - 0.04, and in this case the absorption does not necessarily imply anomalously low excitation temperatures.

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