Line Emission from Water Molecules in Dense Interstellar Shock Waves.

Details Line Emission from Water Molecules in Dense Interstellar Shock Waves. Line Emission from Water Molecules in Dense Interstellar Shock Waves.

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........12k&link_type=abstract

Thesis (PH.D.)--THE JOHNS HOPKINS UNIVERSITY, 1995.Source: Dissertation Abstracts International, Volume: 56-06, Section: B, page

Astronomy and Astrophysics

Astronomy

2

Scientific paper

Non-dissociative shock waves propagating into dense molecular gas produce large abundances of water and give rise to luminous masing and non-masing water emission. I have calculated the structure of non-dissociative shock waves propagating into: (1) the very dense molecular gas (10^7 >=q n(H _2)/cm^{-3} >=q 10^{9.5}) thought to give rise to water maser emission in star forming regions; and (2) the somewhat less dense molecular gas (10 ^4 >=q n(H_2)/cm ^{-3} >=q 10 ^{6.5}) thought to make up the bulk of the gas in bipolar molecular outflows. My calculation of the shock structure includes a new careful treatment of the role of dust grains in the dynamics of these shock waves, as well as newly computed molecular cooling rates based on the most accurate molecular data currently available. I calculate the line emission from the water molecules produced in these shock waves. I find that shocks in the very dense gas gives rise to strong water maser emission in numerous submillimeter, millimeter and centimeter wavelength transitions and that my model can account for measurements of maser line ratios which cannot be explained on the basis of models which compute the water maser emission behind dissociative shocks. The lower density shocked gas gives rise to bright non-masing emission in numerous far-infrared and submillimeter transitions of water as well as the molecules CO, H _2 and OH. I make predictions for the strengths of a series of water transitions as a function of shock parameters. My calculations show that non-masing water emission should be detectable for the first time using the Infrared Space Observatory and the Sub-millimeter Wave Astronomy Satellite. I also present measurements of the 22 GHz and 321 GHz water maser emission from the W49 galactic star forming region. I make feature-by-feature comparisons of the emission in the two lines and compare the data with the predictions from my model of water maser emission. The data are consistent with the maser emission arising either from fast dissociative shocks or from slow (v_ {s} < 15 km s ^{-1}) non-dissociative shocks.

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