PROJECT-J: The Shocking H ₂ Outflow from HH 46

Abstract We analyze the H 2 emission observed in the HH 46 Class I system as part of PROtostellar JEts Cradle Tested with JWST (PROJECT-J), to investigate the origin and excitation of the warm molecular outflow. We used NIRSpec and MIRI spectral maps (1.6–27.9 μ m) to trace the structure and physical conditions of the outflow. By fitting the H 2 rotational diagrams with a multitemperature gas model, we derived key physical parameters, including temperature, extinction, column densities, and the ortho-to-para ratio. This information is combined with a detailed kinematical analysis and comparison with irradiated shock models. We find no evidence of H 2 temperature or velocity stratification from the axis to the edge of the outflow, as would be expected in MHD disk-wind models and as observed in other outflows. Instead, the observations suggest that the H 2 emission arises from shock interactions of jet bow shocks and/or wide-angle winds with the ambient medium and cavity walls. NIRSpec emission and velocity maps reveal expanding molecular shells, likely driven by the less luminous source in the binary system. We infer an accretion rate of ≲10 −9 M ⊙ yr −1 for the secondary source, approximately one order of magnitude lower than that of the primary. The H 2 emission is consistent with excitation by low-velocity (∼10 km s −1 ) J-type shocks, irradiated by an external UV field that may originate from strong dissociative shocks driven by the atomic jet. Future JWST observations will further constrain the evolution of the expanding shell and the mechanisms driving the outflow.