[Fe II] jets from intermediate-mass protostars in Carina

Abstract

We present new HST/WFC3-IR narrow-band [Fe II] images of protostellar jets in the Carina Nebula. Combined with five previously published sources, we have a sample of 18 jets and two Herbig-Haro (HH) objects. All of the jets we targeted with Wide-Field Camera 3 (WFC3) show bright infrared [Fe II] emission, and a few Hα candidate jets are confirmed as collimated outflows based on the morphology of their [Fe II] emission. Continuum-subtracted images clearly separate jet emission from the adjacent ionization front, providing a better tracer of the collimated jet than Hα and allowing us to connect these jets with their embedded driving sources. The [Fe II] 1.64 μm/Hα flux ratio measured in the jets is ≳5 times larger than in the adjacent ionization fronts. The low-ionization jet core requires high densities to shield Fe⁺ against further ionization by the FUV radiation from O-type stars in the H II region. High jet densities imply high mass-loss rates, consistent with the intermediate-mass driving sources we identify for 13 jets. The remaining jets emerge from opaque globules that obscure emission from the protostar. In many respects, the HH jets in Carina look like a scaled-up version of the jets driven by low-mass protostars. Altogether, these observations suggest that [Fe II] emission is a reliable tracer of dense, irradiated jets driven by intermediate-mass protostars. We argue that highly collimated outflows are common to more massive protostars, and that they suggest the outflow physics inferred for low-mass stars formation scales up to at least ∼8 M_⊙.