Anatomy of HH 111 from CO Observations: A Bow‐Shock‐driven Molecular Outflow

We present millimeter line observations of the HH 111 outflow and its drivingsource. The molecular gas emission observed with IRAM 30m and the CSO reveals asmall condensation of cold and dense gas. The low-velocity outflow has beenmapped with the IRAM PdBI interferometer. The cold gas is distributed in ahollow cylinder surrounding the optical jet. The formation of this cavity andits kinematics are well accounted for in the frame of outflow gas entrainmentby jet bow shocks. Evidence of gas acceleration is found along the cavitywalls, correlated with the presence of optical bow shocks. The cavity has beenexpanding with a mean velocity of 4 km/s on a timescale of 8700 yr, similar tothe dynamical age of the optical jet. The separation of the inner walls reaches8"-10", which matches the transverse size of the wings in the bow shock. CSOobservations of the J=7-6 line show evidence of a high-velocity and hot gascomponent (T=300-1000 K) with a low filling factor, associated with shockedmolecular gas in the jet. [CI] observations are consistent with C-typenon-dissociative shocks. Mapping of the high-velocity molecular bullets B1-B3located beyond the optical jet, with the PdBI, reveals small structures of 3"by 7" flattened perpendicular to the flow direction. They are made of cold gasof moderate density(a few 10^3 cm-3). The bullets appear to expand into thelow-density surrounding medium. We conclude that they are probably shocked gasknots resulting from past time-variable ejections in the jet.Comment: 21 pages + 4 figures (JPG). To appear in Astrophysical Journa