FUSE Deuterium Observations: A Strong Case For Galactic Infall

Understand

Measurements of deuterium in the local interstellar medium have revealed large variations in D/H along different lines of sight.

• Moreover, recent {\it Far Ultraviolet Spectroscopic Explorer} (FUSE) measurements find D/H to be anticorrelated with several indicators of dust formation and survival, suggesting that interstellar deuterium suffers significant depletion onto dust grains.
• This in turn implies that the total deuterium abundance in the local Galactic disk could be as high as $\sim 84 %$ of the primordial D abundance.
• It was proposed that the infall/accretion of pristine gas is needed to explain such a high deuterium abundance.