The Deuterium Abundance In The Galactic Center 50 km/s Molecular Cloud: Evidence For A Cosmological Origin Of D

Abstract

We confirm that deuterium exists in the Galactic Center (GC) and estimate that D/H = 3 × 10−6 using a new 5192-chemical reaction model. This is the lowest D/H ratio observed in the Galaxy, five times lower than the local ISM D/H = 1.5 × 10−5 but 106 × larger than D/H predicted by GC models. We detected DCN in the GC Sgr A 50 km/s molecular cloud located 10 pc from the GC with the NRAO 12m telescope and obtained T*R = 0.061 ± 0.007 K and 0.04 ± 0.02 K for the J = 1-0 and 2-1 lines. The most likely source of the GC D is continuous injection from the infall of primordial matter with D/H = 5 × 10−5 with the D/H determined by astration and mixing. Thus there are no significant Galactic sources of D and no recent quasar or AGN activity in the GC. This primordial D/H implies that the baryon density is less than the density necessary to close the Universe; most of the baryons are in dark matter; and there are fewer than four ν families.