Deuterium in the Sagittarius B2 and Sagittarius A galactic center regions

We report IRAM 30-m observations of DCN and DCO+ towards the galactic cente r molecular clouds Sgr B2 and SgrA. We compare our results with simultaneou s measurements of H-13 CN and (HCO+)-O-18 in order to derive estimates of t he [DCN]/[HCN] and [DCO+]/[HCO+] abundance ratios. We mapped Sgr B2 in DCN( 2-1) and DCN(3-2) and we com pared (HCN)-N-15 with DCN for one position of our maps. The uncertainties in such measurements turn out to be large, due to optical depth effects, in the case of (HCN)-C-13, and, in the case of Sg r B2, due to the strong foreground absorption in (HCN)-C-13, (HCN)-N-15 and (HCO+)-O-18. Taking these effects into account, we conclude that [DCN]/[HC N] towards the molecular ridge in Sgr B2 is 1.3 10(-4) (uncertain by a fact or 2) and towards the Sgr A molecular cloud is < 6 10(-4). Towards SgrB2, w e also estimate [DCO+]/[HCO+] to be 2 10(-4) again with a factor of 2 uncer tainty. We have carried out model calculations to estimate the amount of de uterium enhancement in these species in these clouds. We find, for temperat ures between 40 and 120 K, that one expects D to be enhanced in DCN in the galactic center by a factor between 12 and 140 over the actual ratio of [D/ H]. The corresponding enhancement for DCO+ would be between 23 and 460. Bas ed on these results, we conclude that the ratio of [D/H] in the Sgr B2 clou d is 5 10(-6) with a factor of 10 uncertainty. This result, while it has la rge uncertainty, suggests that deuterium is roughly one order of magnitude less abundant in the galactic center than in the solar neighbourhood. We br iefly discuss possible consequences of this for the stellar initial mass fu nction in the galactic center.