Deuterium in the Galactic Center: Evidence for a Cosmological Origin of D and the Infall of D Enriched Gas
Abstract
If deuterium is produced via any stellar or Galactic nucleosynthesis process, then its abundance would be a maximum value in the Galactic Center (GC). Conversely, if there are no additional Galactic source of D, then astration would reduce the initial D abundance in the GC by 107 to D/H = (2-4)×10-12. We used the Arizona Radio Observatory and detected the J = 1-0 lines of DCN and H15CN in four GC molecular clouds located from 10-100 pc from the GC (Sgr A 50 km s-1; Sgr A 20 km s-1; Sgr B2; and G0.13-0.13 in the magnetic arc). We did not detect DCN or H15CN in the circumnuclear disk located 2 pc from the GC where any D is probably destroyed by a faster rate of astration. We used a 5300 chemical reaction model to analyze DCN (used to trace D) and D fractionation, which always enhances the abundance of D molecules. We estimate the underlying D/H ratio in the GC to be D/H = (2-5)×10-6 which is in agreement with the results of Lubowich et al. (2000, Nature, 405, 1025; D/H = 1.7×10-6) from DCN observations in one GC cloud. The GC D/H ratios are less than the local ISM D/H ratio but 106 times larger than D/H ratios predicted by chemical evolution models without an additional source of D. The most likely source of this additional D is the continuous infall of low-metallicty gas enhanced with D which would negate much of the effects of astration. Thus, there are no significant Galactic sources of deuterium, D is primarily cosmological, and the Galaxy has not had quasar or AGN activity in the past 1 Gyr.
DAL was supported by an AAS Small Research Grant- Publication:
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American Astronomical Society Meeting Abstracts #207
- Pub Date:
- June 2006
- Bibcode:
- 2006AAS...20721703L