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1 The [D/H] abundance derived from protostellar outflows across the Galactic disk measured with JWST Read the paper here! Logan Francis
Deuterium and Galactic Chemical Evolution ●Primordial D created in Big Bang, only depleted in stellar interiors D + p → 3He + γ ●BBN models indicate primordial [D/H] of 2.58 ± 0.13 × 10-5, in good agreement with observational constraints (Cyburt+ 2016) 2 Mixing and inhomogeneity? ●Models of Galactic chemical evolution generally predict [D/H] to decrease towards the Galactic center Primordial [D/H]
How can we measure [D/H]? 3 Tracer Complex Deuterated Molecules, e.g. DCN/HCN ISM D I and H I absorption lines HD and H2 Example studies Penzias et al. 1977, 1979 Linsky et al. 2006, Prodanović et al. 2010 Neufeld et al. 2006, Yuan et al. 2012 𝝺sub-mm/radio (ground) UV (space) mid-IR/far-IR (space) Pros Rotational transitions easily detectable in ground-based observations Direct comparison of H and D Nearly direct measurement of [D/H] Simple chemical fractionation Cons Highly uncertain due to complex chemical fractionation Blending with O I lines Saturated at large distances Weak emission lines
But is some Deuterium locked up in grains? ●C-D bond much stronger than C-H bond → D can be efficiently locked up in PAHs and carbonaceous dust grains (Jura 1982, Tielens 1983, Draine 2006). ●Scatter in [D/H] from UV absorption lines outside local bubble argued to be due to varying depletion of D into dust grains (Linksy et al. 2006) 4 log(105 [D/H]) local bubble non-local bubble Prodanović et al. 2010 Primordial [D/H] = 2.58 x 10-5 LB median ~ 1.6 x 10 -5
Detection of deuterated PAHs with JWST ●Deuterated PAHs can account for a large fraction of ‘missing’ D (Draine et al 2006) ●Orion bar observed aliphatic NPAD/NPAH ~3% (Peeters et al. 2024) 5 PADs, 4.646 micron aliphatic bond
Measuring [D/H] with JWST/MIRI ●H2 and HD have many transitions in JWST MIRI/MRS range (4.9-28 micron) ●Last facilities capable of this were Spitzer and ISO - huge sensitivity improvements with JWST 6
Observations of protostars across the Galactic disk ●MIRI/MRS observations of 5 low-mass, nearby protostars + 5 high-mass, distant targets from the JOYS programs (1290, 1257) ●All targets have H2 bright outflows. Low-mass outflows resolved are spatially well-resolved. 7
Line Moment maps: HH 211 Brightest HD emission in sample located towards strong shock knots traced by [Fe I], [Fe II], [S I], H2 S(7) 8
Measuring [D/H] from HD and H2 ●Extract spectra towards positions with bright H2 and construct rotation diagrams for H2 and HD ●Extinction, H2 ortho-to-para ratio, included as free parameters in fit ●Calculate [D/H] abundance from HD and warm H2 column density: [D/H] = 1/2 x NHD x HDcorr / NH2,warm ●Correction factor HDcorr takes into account subthermal excitation and conversion of HD → D in shocks (Bertoldi +1999) 9
HD column density correction factor 16 HDcorr includes: ●Chemical conversion of HD to D: ●Sub-thermal excitation of HD (n < ncrit ~ 106 cm-3) Effects work in opposite directions - combined effect is is approximately constant across a wide range of shock conditions with HDcorr = 2.54 (Bertoldi+1999) themal sub-thermal
HD column density correction factor 17 HDcorr includes: ●Chemical conversion of HD to D: ●Sub-thermal excitation of HD (n < ncrit ~ 106 cm-3) Effects work in opposite directions - combined effect is is approximately constant across a wide range of shock conditions with HDcorr = 2.54 (Bertoldi+1999)
Rotation Diagram and [D/H] Results 18
Measuring [D/H] with JWST/MIRI ●Both H2 and HD have multiple transitions in JWST MIRI/MRS range (4.9-28 micron) ●Last facilities capable of this were Spitzer and ISO - huge sensitivity improvements with JWST ISO (1995-1998) Spitzer (2003-2009) JWST (2021-Present) 19
[D/H] variations in our Galaxy Models of Galactic chemical evolution generally predict [D/H] to decrease towards the Galactic center: 20 Romano et al. 2006 van de Voort et al. 2018
Additional moment maps: IRAS 23385, IRAS 18089 21
