Nitrogen is a key element for building habitable worlds, yet only a small fraction of the available N-budget of planet-forming disks has been detected. In particular, the lack of any IR NH3 detection is striking, as this molecule is predicted to be rather abundant in the warm, inner regions of protoplanetary disks and therefore potentially readily incorporated into (giant) planets’ atmospheres. We present a combined modeling and observational study of N-bearing molecules in planet-forming disks, using detailed thermo-chemical disk models that investigate the sensitivity of N-containing molecules to the bulk elemental composition of the disk. Our models predict a strong increase in HCN flux with high C/H and conversely, a strong increase in flux from NO when O/H is high. The flux from NH3 is not very sensitive to O/H, but it does decrease at high C/H due to competition with HCN. However, the absolute NH3 flux predicted by our model is not large enough to be detected with JWST-MIRI, even when N/H is enhanced by an order of magnitude. The flux from NO, on the other hand, is potentially detectable and could therefore provide further insights into the N-budget of the inner disk. Using a cross-correlation technique, we search for NH3 and NO detections in three disks, GW Lup, Sz 98, and V1094 Sco. We do not find any NH3 detections and only one tentative NO detection in V1094 Sco, though this needs further study to be confirmed. Additionally, we demonstrate that future facilities in the FIR may provide a better opportunity to detect NH3 and thereby draw a comparison to the NH3 budget known to be present in interstellar ices.
Vlasblom et al. (Thu,) studied this question.