Proper motions of collimated jets from intermediate-mass protostars in the Carina Nebula

Abstract

We present proper motion measurements of 37 jets and HH objects in the Carina Nebula measured in two epochs of Hα images obtained ~10 yr apart with Hubble Space Telescope/ Advanced Camera for Surveys (ACS). Transverse velocities in all but one jet are faster than ≳ 25 km s-1, confirming that the jet-like Hα features identified in the first epoch images trace outflowing gas. Proper motions constrain the location of the jet-driving source and provide kinematic confirmation of the intermediate-mass protostars that we identify for 20/37 jets. Jet velocities do not correlate with the estimated protostar mass and embedded driving sources do not have slower jets. Instead, transverse velocities (median ~75 km s-1) are similar to those in jets from low-mass stars. Assuming a constant velocity since launch, we compute jet dynamical ages (median ~104 yr). If continuous emission from inner jets traces the duration of the most recent accretion bursts, then these episodes are sustained longer (median ~700 yr) than the typical decay time of an FU Orionis outburst. These jets can carry appreciable momentum that may be injected into the surrounding environment. The resulting outflow force, dP/dt, lies between that measured in low- and high-mass sources, despite the very different observational tracers used. Smooth scaling of the outflow force argues for a common physical process underlying outflows from protostars of all masses. This latest kinematic result adds to a growing body of evidence that intermediate-mass star formation proceeds like a scaled-up version of the formation of low-mass stars.