JOYS+: Analyses of OCN^-, N₂O, NO, and complex cyanides in ices: Thermal processing results in a modest increase of OCN⁻ ice

July 2026 • 2026A&A...711A.240N

Authors • Nazari, P. • Brunken, N. • Chen, Y. • Slavicinska, K. • van Dishoeck, E. F. • Rocha, W. R. M. • Boogert, A. C. A. • Navarro, M. G. • Le Gouellec, V. J. M. • Francis, L. • Tychoniec, L. • Caratti o Garatti, A. • Gieser, C. • Greene, T. P. • Kavanagh, P. J.

Abstract • Context. Nitrogen-bearing molecules are generally more difficult to observe than oxygen-bearing ones in both gas and ice, mainly due to the lower abundance of nitrogen in the interstellar medium. Therefore, the formation pathways of many of these species is still under debate. Aims. Studies prior to the launch of the James Webb Space Telescope (JWST) did not have the sensitivity to observe ices toward the youngest and most deeply embedded Class 0 objects. The time is now ripe to study nitrogen-bearing molecules toward ice-rich Class 0 and Class I objects with the JWST. Here we focus on OCN⁻, CH₃CN, C₂H₅CN, NO, and N₂O in ices to better understand their formation. Methods. We used the data from JWST Observations of Young protoStars (JOYS+) program. Particularly, we studied the objects that have the JWST NIRSpec-IFU observations (8 Class 0 and 11 Class I) to measure the ice column densities of the targeted molecules. Results. We firmly detect OCN⁻ in ices for all these objects, tentatively detect CH₃CN, C₂H₅CN, and N₂O toward three sources, and find upper limits on the NO abundance in ices. The OCN⁻/CO₂ ratios are found to be higher by a factor of ~2─3 for the objects that have a visible CO₂ (15.2 μm) double peak (a sign of ice thermal processing), which points to the moderate effect of temperature on OCN⁻ production. Considering H₂O, CO₂, and OCN⁻ relations with A_V, we tentatively find that OCN⁻ forms at a later stage compared to H₂O and CO₂. We find that the ratios of CH₃CN, C₂H₅CN, and N₂O with respect to OCN⁻ are relatively constant within one order of magnitude across our objects, likely suggesting that they have similar ice environments. The upper limit abundances of NO are around one order of magnitude lower than what was previously predicted in ices of a mature protoplanetary disk to explain the gas-phase detection of this molecule in the disk. This indicates that gas-phase NO may be a product of another molecule such as N₂O in the ices. Conclusions. We conclude that after OCN⁻ forms, it can increase at higher temperatures by only a factor of ~2─3, and thus OCN⁻ detection alone does not imply ice heating. Large-sample studies of OCN⁻ toward pre-stellar cores will be useful to further confirm the formation timeline of this molecule.

Links

• POSTSCRIPT https://www.aanda.org/10.1051/0004-6361/202557830/postscript
• PREPRINT http://arxiv.org/abs/2604.25915