Context. Complex organic molecules (COMs) are commonly detected in and near star-forming regions. However, the dominant process in the release of these COMs from the icy grains – where they predominately form – to the gas phase is still an open question. Aims. We investigate the origin of COM emission in a high-mass protostellar source, CygX-N30 MM1, through high-angular-resolution interferometric observations over a continuous broad frequency range. Methods. We used 32 GHz Submillimeter Array observations with continuous frequency coverage from 329 to 361 GHz at an angular resolution of ~1″ to do a line survey and obtain a chemical inventory of the source. The line emission in the frequency range was used to determine column densities and excitation temperatures for the COMs. We also mapped out the intensity distribution of the different species. Results. We identified approximately 400 lines that can be attributed to 29 different molecular species and their isotopologues. We find that the molecular peak emission is along a linear gradient, and coincides with the axis of red- and blueshifted H2CO and CS emission. Chemical differentiation is detected along this gradient, with the O-bearing molecular species peaking towards one component of the system and the N- and S-bearing species peaking towards the other. The chemical gradient is offset from but parallel to the axis through the two continuum sources. The inferred column densities and excitation temperatures are compared to other sources where COMs are abundant. Only one deuterated molecule is detected, HDO, while an upper limit for CH2DOH is derived, leading to a D/H ratio of <0.1%. Conclusions. We conclude that the origin of the observed COM emission is probably a combination of the young stellar sources along with accretion of infalling material onto a disc-like structure surrounding a young protostar and located close to one of the continuum sources. This disc and protostar are associated with the O-bearing molecular species, while the S- and N-bearing species on the other hand are associated with the other continuum core, which is probably a protostar that is slightly more evolved than the other component of the system. The low D/H ratio likely reflects a pre-stellar phase where the COMs formed on the ices at warm temperatures (~30 K), where the deuterium fractionation would have been inefficient. The observations and results presented here demonstrate the importance of good frequency coverage and high angular resolution when disentangling the origin of COM emission.

Context. The chemistry of sulphur-bearing species in the interstellar medium remains poorly understood, but might play a key role in the chemical evolution of star-forming regions. Aims. Coupling laboratory experiments to observations of sulphur-bearing species in different parts of star-forming regions, we aim to understand the chemical behavior of the sulphur species in cold and warm regions of protostars, and we ultimately hope to connect them. Methods. We performed laboratory experiments in which we tested the reactivity of hydrogen sulfide (H2S) on a cold substrate with hydrogen and/or carbon monoxide (CO) under different physical conditions that allowed us to determine the products from sulphur reactions using a quadrupole mass spectrometer. The laboratory experiments were complemented by observations. We observed two luminous binary sources in the Cygnus-X star-forming complex, Cygnus X-N30 and N12, covering a frequency range of 329–361 GHz at a spatial resolution of 1′′5 with the SubMillimeter Array (SMA). This study was complemented by a 3 mm line survey of Cygnus X-N12 covering specific frequency windows in the frequency ranges 72.0–79.8 GHz at a spatial resolution of 34′′0–30′′0 and 84.2–115.5 GHz at a spatial resolution of 29′′0–21′′0, with the IRAM-30 m single-dish telescope. Column densities and excitation temperatures were derived under the local thermodynamic equilibrium approximation. Results. We find that OCS is a direct product from H2S reacting with CO and H under cold temperatures (T < 100 K) from laboratory experiments. OCS is therefore found to be an important solid-state S-reservoir. We identify several S-species in the cold envelope of Cyg X-N12, principally organo-sulphurs (H2CS, CS, OCS, CCS, C3S, CH3SH, and HSCN). For the hot cores of Cyg X-N12 and N30, only OCS, CS and H2CS were detected. We found a difference in the S-diversity between the hot core and the cold envelope of N12, which is likely due to the sensitivity of the observations toward the hot core of N12. Moreover, based on the hot core analysis of N30, the difference in S-diversity is likely driven by chemical processes rather than the low sensitivity of the observations. Furthermore, we found that the column density ratio of NCS/NSO is also an indicator of the warm (NCS/NSO > 1), cold (NCS/NSO < 1) chemistries within the same source. The line survey and molecular abundances inferred for the sulphur species are similar for protostars N30 and N12 and depends on the protostellar component targeted (i.e., envelope or hot core) rather than on the source itself. However, the spatial distribution of emission toward Cyg X-N30 shows differences compared to N12: toward N12, all molecular emission peaks on the two continuum sources, whereas emission is spatially distributed and shows variations within molecular families (N, O, and C families) toward N30. Moreover, this spatial distribution of all the identified S-species is offset from the N30 continuum peaks. The sulphur-bearing molecules are therefore good tracers to connect the hot and cold chemistry and to provide insight into the type of object that is observed.