The First Detection of Deuterated Molecular Hydrogen at z < 1.7 Beyond the Milky Way Galaxy
Abstract
We report on the first detection of deuterated molecular hydrogen, HD, at a redshift < 1.7 beyond the Milky Way galaxy. HD and H2 are detected in HST/COS data of a low metallicity (Z ~ 0.07Z_sun) damped Lyα system at z = 0.18562 toward QSO B0120-28, with log N(H I) = 20.50 +/- 0.10. Four absorption components are clearly resolved in H2 while two components are resolved in HD; the bulk of the molecular hydrogen is associated with the components traced by HD. We find total column densities log N(HD) = 14.82 +/- 0.15 and log N(H2) = 20.00 +/- 0.10. This system has a high molecular fraction, f(H2) = 0.39 +/- 0.10 and a low HD to H2 ratio, log (HD/2xH2) = -5.5 +/- 0.2 dex. The excitation temperature, T01 = 65 +/- 2 K, in the component containing the bulk of the molecular gas is lower than in other DLAs. These properties are unlike those in other DLA systems but are consistent with what is observed in dense clouds in the Milky Way.
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22324302O