(DOI: will be inserted by hand later) Shock-induced PDR in the Herbig-Haro object HH 2

tomorrow; yesterday Abstract. We report mid-infrared (5 − 17µm) and SO, CO, 13CO millimeter line observations of the protostellar jet HH 2 and the parental molecular cloud. We have detected for the first time mid-infrared emission along a protostellar jet. We find that the outflowing gas extends much further away than the Herbig-Haro object HH 2, showing direct evidence that downstream gas has been accelerated by previous outflow events. These gas layers appear to have been detached from the parental cloud, as they are distributed around a cavity, probably dug by protostellar outflow(s). SO emission is detected in shocked gas regions associated with outflows. The UV field produced in the strong shock region HH 2H-A has produced a low-excitation Photon-Dominated Region at the walls of the cavity, which is detected in the PAH emission bands and in the continuum between 5 and 17µm. This continuum arises from very small grains transiently heated by a FUV field G ≃ 20G0, which probably formed from evaporation of dust grain mantles in shocks