A Parsec‐Scale Herbig‐Haro Jet in Barnard 5

Abstract

We report the discovery of a parsec-scale, jetlike, bipolar Herbig-Haro flow, HH 366, emerging from the young stellar object IRS 1, which is embedded in the dark cloud Barnard 5 (B5) at the eastern end of the Perseus molecular cloud complex. The jet is about 22' in extent, which corresponds to a projected length of about 2.2 pc (assuming a distance of 350 pc), and is less than 1' (0.1 pc) wide. The brighter southwestern end of the jet is receding, with a velocity between 30 and 100 km s–1. The fainter eastern lobe is blueshifted with a slightly lower radial velocity amplitude. The blueshifted jet emerges from IRS 1 at a position angle of about 75°. Both the redshifted and blueshifted portions of the flow are brightest at their ends (the most distant points from the source). In the blueshifted eastern lobe, faint emission can be traced to within several arcminutes of the source, while the redshifted lobe emerges from behind the cloud core about 5' southwest of IRS 1.The orientation and kinematics of the Herbig-Haro jet matches that of the inner portion of the CO outflow from IRS 1 mapped at high-angular resolution by Fuller et al. A reanalysis of the Goldsmith et al. 12CO data shows that an envelope of high-velocity molecular gas extends from IRS 1 to both the eastern and western ends of the Herbig-Haro jet. The redshifted lobe of CO emission lying several arc-minutes north of IRS 3 (an infrared source located about 10' to the southwest of IRS 1) coincides with the southwestern (redshifted) optical lobe of the B5 jet. Although previously associated with IRS 3, this lobe is the brightest portion of the southwestern lobe of the IRS 1 CO outflow. Both the CO flow and the HH jet are nearly orthogonal to a 0.06 pc long ridge or extended pseudodisk of dense molecular gas seen in tracers such as HCN. The two lobes of the IRS 1 optical outflow are misaligned; the redshifted lobe appears to be deflected south with respect to the axis inferred by connecting B5 IRS1 to the end of the blueshifted lobe. A roughly 5-10 km s–1 motion of the source with respect to the host cloud could produce this misalignment. The IRS 1 outflow provides evidence for outflow models in which CO is entrained from dense molecular gas by a hypersonic jet.A second Herbig-Haro flow, HH 367, is located 1' southeast (at position angle 155°) of the infrared source B5 IRS 3.