Star formation time-scale in the molecular filament WB 673

Abstract

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 tchem = 1-3 × 105 yrs, providing the best agreement between the simulated and observed column densities in all the clumps. Therefore, we consider tchem 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.