2022MNRAS.517.4669R

We present the observations of ammonia emission lines toward the interstellar filament WB 673 hosting the dense clumps WB 673, WB 668, S233-IR, and G173.57+2.43. LTE analysis of the lines allows us to estimate gas kinetic temperature (≲30K in all the clumps), number density (7-17 × 10³ cm^–3), and ammonia column density (≈1-1.5 × 10¹⁵ cm^–2) in the dense clumps. We find signatures of collapse in WB 673 and presence of compact spatially unresolved dense clumps in S233-IR. We reconstruct 1D density and temperature distributions in the clumps and estimate their ages using astrochemical modelling. Considering CO, CS, NH₃, and N₂H⁺ molecules (plus HCN and HNC for WB 673), we find a chemical age of t_chem = 1-3 × 10⁵ yrs, providing the best agreement between the simulated and observed column densities in all the clumps. Therefore, we consider t_chem as the chemical age of the entire filament. A long preceding low-density stage of gas accumulation in the astrochemical model would break the agreement between the simulated and observed column densities. We suggest that rapid star formation over a ∼10⁵ yrs time-scale take place in the filament.