PRODIGE – envelope to disk with NOEMA

Context . Determining the amount of sulfur in volatiles and refractories in the interstellar medium remains one of the main problems in astrochemistry. The detection of H 2 S ices, which are thought to be one of the main sulfur reservoirs, is still a great challenge and has not been achieved yet, and the only sulfur-bearing species detected in the ices to date is OCS. The PROtostars and DIsks: Global Evolution (PRODIGE) large survey observations with the NOrthern Extended Millimeter Array (NOEMA) of several Class 0/I protostars in the Perseus Molecular Cloud provide a perfect opportunity to study the H 2 S and OCS composition of the ices through the volatiles sublimated in the warm inner core (T>100K, n ~10 6 cm –3 ) of these protostars. Aims . Our aim is to determine the H 2 S/OCS ratio in the warm inner core of the protostars of our sample in order to study how it is affected by different factors during its evolution. Methods . We used the NOEMA millimeter observations from the PRODIGE program of H 2 S, H 2 33 S, OCS, OC 33 S, and OC 34 S to estimate the H 2 S and OCS column densities in the warm inner core of 24 protostars of Perseus. In addition, we used SO and SO 2 data from the Atacama Large Millimeter/submillimeter Array (ALMA) archive to complete the sulfur budget and give a rough estimate of the total sulfur abundance in each of the sources. We explored the chemistry of H 2 S and OCS in the warm cores using chemical and dynamical simulations of the collapse of a dense core to form a protostar. Results . The compound H 2 S is detected in 21 protostars and OCS in 17 protostars of our sample. The estimated H 2 S/OCS ratio reveals a segregation of the sources into “OCS-poor” and “OCS-rich” protostars, where the OCS-poor protostars present higher H 2 S/OCS ratios than the OCS-rich ones. The total sulfur abundance, which is always dominated by either H 2 S or OCS, grows with evolution during the Class 0 phase, reaching a minimum depletion of a factor less than eight in the Class 0/I objects and decreasing again in the Class I. Chemo-MHD simulations show that temperature changes in the pre-stellar phase and during the collapse can produce substantial differences in the H 2 S and OCS (ice and gas-phase) abundances and in the H 2 S/OCS ratio. Conclusions . Our analysis shows that the H 2 S/OCS ratio is strongly influenced by the environment and the initial conditions of the cloud.