Molecular abundances in the Magellanic Clouds II. Deuterated species in the LMC
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The first definite discoveries of extragalactic deuterium are reported. DCO$^+$ has been detected in three and DCN has been measured in one star-forming region of the Large Magellanic Cloud (LMC). While the HCO$^+$/DCO$^+$ abundance ratios are found to be 19 $\pm$ 3, 24 $\pm$ 4, and 67 $\pm$ 18 for N113, N44BC and N159HW, respectively, a HCN/DCN abundance ratio of 23 $\pm$ 5 is obtained for N113. These results are consistent with a gas temperature of about 20\,K and a D/H ratio of about $1.5 \times 10^{-5}$, consistent with that observed in the Galaxy. If the cloud temperature is closer to 30\,K, then a D/H ratio is required to be up to an order of magnitude larger. Because this ratio provides a lower limit to the primordial D/H ratio, it indicates that the baryon mass density alone is unable to close the universe.
4 pages uuencoded gzip-compressed .tar file including one figures, To appear in A&A Letter, further comments: please contact Yi-nan Chin (einmann@biaa21.biaa.sinica.edu.tw)
4 pages uuencoded gzip-compressed .tar file including one figures, To appear in A&A Letter, further comments: please contact Yi-nan Chin (einmann@biaa21.biaa.sinica.edu.tw)