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Letter to the Editor
DI in the outer Galaxy
Jayaram N. Chengalur 1,
Robert Braun 1 and
W. Butler Burton 2
Received 15 November 1996 / Accepted 9 January 1997
We report on a deep search with the Westerbork Synthesis Radio Telescope towards the galactic anticenter for the 327 MHz hyperfine transition of DI. This is a favorable direction for a search because: (i) the HI optical depth is high due to velocity crowding; (ii) the observed molecular column density is low (implying that most of the deuterium would probably be in atomic form, rather than in HD); and (iii) the stellar reprocessing should be minimal.
Our observations are about a factor of two more sensitive than previous searches for DI in this direction. We detect a low significance () feature, consistent in both amplitude and center frequency with an emission feature reported previously (Blitz & Heiles 1987). If this is the DI line, then the implied of is comparable to the inferred pre-solar deuterium abundance. Our observation is consistent with the recent low measurements of D/H towards high-redshift Lyman-limit systems. On the other hand, if the reports of high DI abundance () in such systems are confirmed, then our observations imply that even in regions of reduced star formation within the outer Galaxy, the DI abundance has been reduced by a factor of from the primordial abundance.
Key words: Cosmology: observations ISM: abundances Galaxy: abundances Radio lines: ISM
Send offprint requests to: Robert Braun
Online publication: July 8, 1998