Paper detail

Identification of solid N2O in interstellar ices using open JWST data

Context. There are only six molecules containing N-O bond that are detected in gaseous phase in interstellar medium. One of those is nitrous oxide (N2O), which was searched for but not found in solid form from as early as Infrared Space Observatory (ISO) mission was launched. The observational capabilities of James Webb Space Telescope (JWST) present a possibility to identify solid interstellar N2O. Aims. We aim to identify nitrous oxide in open JWST spectra of interstellar ices towards a sample of Class 0, 0/I and flat protostars using the relevant laboratory mixtures of N2O-bearing interstellar ice analogues. Methods. A set of laboratory infrared transmission spectra was obtained for the following mixtures: N2O:CO2=1:20, N2O:CO=1:20, N2O:N2=1:20, N2O:CO2:CO=1:15:5, N2O:CO2:N2=1:15:13 at 10-23 K. A search for N2O in JWST NIRSpec spectra towards 50 protostars was performed by fitting the 4.44-4.47 um (2250-2235 cm-1) NN-stretch absorption band with new laboratory mixtures of N2O-bearing ices. Results. We claim the first secure identification of N2O in 16 protostars. The fitting results show that N2O is formed predominantly within the apolar layer of the ice mantles, rich in CO, CO2 and N2. The abundance of solid N2O is estimated as 0.2-2.1% relative to solid CO. We present band strengths for N2O in the mixtures corresponding to the apolar layer. Also, an identification of the C-N stretch band at 4.42 um (2260 cm-1) is reported, which we tentatively assign to HNCO, the simplest C-N bond carrier.