1997A&A...318L..35C

We report on a deep search with the Westerbork Synthesis Radio Telescope towards the galactic anticenter for the 327MHz hyperfille 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 molacular column density is low (implying that most of the deuterium would probably be in atomic form, rather thall 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 (∼4σ) feature, consistent in both amplitude and center frequency with an emission feature reported previously (Blitz & Heiles 1987ApJ...313L..95B). If this is the DI line, then the implied N_D/N_H of 3.9±1.0x10^–5 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 (∼24x10^–5) 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 ∼6 from the primordial abundance.