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Astron. Astrophys. 318, L35-L38 (1997)

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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

1 Netherlands Foundation for Research in Astronomy, P.O. Box 2, 7990 AA Dwingeloo, The Netherlands
2 Sterrewacht Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands

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 ([FORMULA]) 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 [FORMULA] of [FORMULA] 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 ([FORMULA]) 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 [FORMULA] from the primordial abundance.

Key words: Cosmology: observations – ISM: abundances – Galaxy: abundances – Radio lines: ISM

Send offprint requests to: Robert Braun

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998