The [D/H] abundance derived from protostellar outflows across the Galactic disk measured with JWST

The total deuterium abundance [D/H] is set by only the creation of deuterium in Big Bang Nucleosynthesis, and its destruction within stellar interiors. Measurements of spatial variations in the total [D/H] can thus provide a probe of Galactic chemical evolution. However, most measurements of [D/H] are only sensitive to the gas-phase deuterium, and the amount of deuterium sequestered in dust grains is debated. With JWST MIRI/MRS, gas-phase [D/H] can be measured at unprecedented sensitivity through observation of mid-IR lines of H_2 and HD, while the refractory component can be probed through various forbidden lines. Using data from the JWST Observations of Young protoStars (JOYS) program, we analyze the gas-phase [D/H] abundance and the distribution of refractory species in protostellar outflows. Maps of the emission lines show HD is correlated with the H_2 S(7), [S I], and [Fe I], which trace high velocity jet knots and bright bow-shocks. We show the gas-phase [D/H] varies between our low-mass sources by up to a factor of ~4, despite these sources likely having formed from gas in the Galactic disk with constant total [D/H]. Most measurements of gas-phase [D/H] from our work produce [D/H] ~< 1.0 x 10^-5, a factor of 2-4 lower than the total [D/H] expected from Galactic chemical evolution models. The variations in the gas-phase [D/H] within the outflows and the low values with respect to models suggest that significant depletion of deuterium into the dust may be occurring.