Near‐Infrared H2and [Feii] Imaging and Spectroscopy of New Jets in the Vela Molecular Clouds

Abstract

We present narrowband imaging in the 2.122 μm transition of H2 and in the 1.644 μm transition of [Fe II] of a sample of 12 protostellar candidates and three Herbig-Haro (HH) objects belonging to the Vela molecular ridge (VMR). Out of the 15 investigated fields, we detected H2 emission in IRS 63, 17, 19, 21, and 8 (according to our catalog), while [Fe II] was observed toward only one source (IRS 8), where a counterjet has been identified for the first time. H2 and [Fe II] images have been combined to trace the different shock conditions along this jet. In addition, a new pure molecular H2 jet was discovered in IRS 17, which results in about 20 knots of emission extending up to 0.3 pc from the central driving source. IR spectroscopy (1.55-2.55 μm) at a resolution of ≈600 of the most prominent knots has revealed a large number of H2 emission lines, which were used to evaluate both the extinction and the excitation temperature along the flow. The observed increase of the excitation temperature with the distance from the central source was interpreted as being due to a decrease of the flow velocity with time or, alternatively, to the fact that internal knots travel in a medium already put into motion by previous shock events. Comparisons with model predictions indicate nondissociative C-shocks as the most likely mechanism for line excitation. Finally, the presence of a common alignment of the detected flows with the Galactic plane indicates that the Galactic B field affects the star formation on large scales in VMR.