Mon. Not. R. Astron. Soc., 476, 4994-5005 (2018/June-1)
Tracing the atomic nitrogen abundance in star-forming regions with ammonia deuteration.
FURUYA K. and PERSSON M.V.
Abstract (from CDS):
Partitioning of elemental nitrogen in star-forming regions is not well constrained. Most nitrogen is expected to be partitioned among atomic nitrogen (N I), molecular nitrogen ( N2), and icy N-bearing molecules, such as NH3 and N2. N I is not directly observable in the cold gas. In this paper, we propose an indirect way to constrain the amount of N I in the cold gas of star-forming clouds, via deuteration in ammonia ice, the [ND2H/NH2D]/[NH2D/NH3] ratio. Using gas-ice astrochemical simulations, we show that if atomic nitrogen remains as the primary reservoir of nitrogen during cold ice formation stages, the [ND2H/NH2D]/[NH2D/NH3] ratio is close to the statistical value of 1/3 and lower than unity, whereas if atomic nitrogen is largely converted into N-bearing molecules, the ratio should be larger than unity. Observability of ammonia isotopologues in the inner hot regions around low-mass protostars, where ammonia ice has sublimated, is also discussed. We conclude that the [ND2H/NH2D]/[NH2D/NH3] ratio can be quantified using a combination of Very Large Array and Atacama Large Millimeter/submillimeter Array observations with reasonable integration times, at least towardsIRAS 16293-2422, where high molecular column densities are expected.
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
astrochemistry - stars: formation - ISM: clouds - ISM: molecules
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