HH 80/81: Structure and Kinematics of the Fastest Protostellar Outflow

Abstract: Hubble Space Telescope images obtained in 2018 are combined with archival HST data taken in 1995 to detect changes and measure proper motions in the HH 80/81 shock complex which is powered by the fastest known jet driven by a forming star, the massive object IRAS 18162-2048. Some persistent features close to the radio jet axis have proper motions grater than 1,000 km/s away from IRAS 18162-2048. About 3 to 5 parsecs downstream from the IRAS source and beyond HH 80/81, H-alpha emission traces the rim of a parsec-scale bubble blown by the jet. Lower speed motions are seen in [Sii] away from the jet axis; these features have a large component of motion at right-angles to the jet. We identify new HH objects and H2 shocks in the counterflow opposite HH 80/81. The northeastern counterflow to HH 80/81 exhibits an extended but faint complex of 2.12 um H2 shocks. The inner portion of the outflow is traced by dim 1.64 um [Feii] emission. The full extent of this outflow is at least 1,500" (about 10 pc in projection at a distance of 1.4 kpc). We speculate about the conditions responsible for the production of the ultra-fast jet and the absence of prominent large-scale molecular outflow lobes.