Cold H2O and CO ice and gas toward the Galactic Center

Details Cold H2O and CO ice and gas toward the Galactic Center Cold H2O and CO ice and gas toward the Galactic Center

Nov 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000esasp.456..119m&link_type=abstract

ISO beyond the peaks: The 2nd ISO workshop on analytical spectroscopy. Eds. A. Salama, M.F.Kessler, K. Leech & B. Schulz. ESA-SP

Physics

Ism: Molecules, Line: Profiles, Infrared

Scientific paper

We use the mid-IR absorption lines of gas-phase CO and h2o, observed with the ISO-SWS toward two sources in the Galactic Centre (Sgr A* and GCS-3), to investigate physical conditions in the cold and quiescent regions of molecular clouds along these lines of sight. Three water vapor lines of the ν2=1 mode, and several lines of the R and P-branches of CO and 13CO are detected. The analysis indicates that the absorbing gas is extremely cold, TK ≃ 10 K, confirming that in must arise in cold, quiescent regions. Column densities are ≃ 6.6 × 1017sci for CO and ≃ 2.0 × 1016sci for h2o\ toward sgra, and somewhat lower values toward GCS-3. The ice phase of these molecules is also detected and quantified, and both the CO/h2o\ ratio (≃ 350) and the gas/solid abundance ratio (≃ 65 for CO and ≃ 0.02 for h2o) are remarkably simimlar along the two lines of sight. The fractional abundance of water vapour is ~ 3 × 10-7, substantially lower than in the active cores of dense clouds, but much higher than recently estimated by the SWAS satellite (Snell et al. 1999). Finally, the total (gas + ice) CO/H2O abundance ratio is ≃ 5 which, assuming that all the H2O was originally formed in the gas phase, implies that H2O formation processes are highly efficient.

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