[O I] 63 µm Jets in Class 0 Sources Detected By Herschel

Abstract

We present Herschel PACS mapping observations of the [O i] 63 μm line toward protostellar outflows in the L1448, NGC 1333-IRAS4, HH 46, BHR 71, and VLA 1623 star-forming regions. We detect emission spatially resolved along the outflow direction, which can be associated with a low-excitation atomic jet. In the L1448-C, HH 46 IRS, and BHR 71 IRS1 outflows this emission is kinematically resolved into blue- and redshifted jet lobes, having radial velocities up to 200 km s^-1. In the L1448-C atomic jet the velocity increases with the distance from the protostar, similarly to what is observed in the SiO jet associated with this source. This suggests that [O i] and molecular gas are kinematically connected and that the latter could represent the colder cocoon of a jet at higher excitation. Mass flux rates ({{\dot{M}}_jet}(O i)) have been measured from the [O i] 63 μm luminosity adopting two independent methods. We find values in the range (1-4) × 10^-7 {{M}_⊙ } yr^-1 for all sources except HH 46, for which an order of magnitude higher value is estimated. {{\dot{M}}_jet}(O i) are compared with mass accretion rates (\dot{M}_acc) onto the protostar and with {{\dot{M}}_jet} derived from ground-based CO observations. {{\dot{M}}_jet}(O i)/\dot{M}_acc ratios are in the range 0.05-0.5, similar to the values for more evolved sources. {{\dot{M}}_jet}(O i) in HH 46 IRS and IRAS4A are comparable to {{\dot{M}}_jet}(CO), while those of the remaining sources are significantly lower than the corresponding {{\dot{M}}_jet}(CO). We speculate that for these three sources most of the mass flux is carried out by a molecular jet, while the warm atomic gas does not significantly contribute to the dynamics of the system.