Complex organic molecules in the young hot core RCW 120 S2

We analyse physical and chemical structure of the hot molecular core RCW120 S2, based on high-sensitivity (2-4 mK) APEX observations at 1.3 mm. The analysis reveals a rich molecular inventory, including complex organic molecules (COMs) such as CH${}_3$OH, CH${}_3$CHO, CH${}_3$OCHO and CH${}_3$OCH. We derive gas temperatures (20-300 K), H${}_2$ densities (10${}^4$-10${}^7$cm${}^{-3}$), and molecular column densities. The detected emission probes a radially stratified envelope, with cooler (<= 60 K) and less dense (10${}^4$-10${}^5$cm${}^{-3}$) outer layers traced by SO, SO2, and c-C${}_3$H${}_2$, while warmer (60-100 K) and denser (10${}^5$-10${}^7$cm${}^{-3}$) inner regions are traced by H${}_2$CO, OCS, and low-excitation CH${}_3$CN. The hot gas (<= 100 K) exhibits broad (8-10 km/s) lines from high-excitation CH${}_3$OH, CH${}_3$CN, HDO, and CH${}_3$OCH${}_3$. Relative molecular abundances of COMs generally agree with astrochemical hot-core models, while methanol appears underabundant and CH${}_3$CN overabundant compared to predictions. We attribute these discrepancies to the need for interferometric observations at intermediate spatial scales to resolve the core’s true filling factor and radial gradients.