A highly collimated outflow in the core of OMC-1

Abstract

The paper reports the discovery of a 120 arcsec long jet of CO in OMC-1. The feature, which is redshifted up to 15 km s-1 from the ambient CO gas, was presumably ejected from CS3/FIR4 60 arcsec southwest of the Trapezium and 110 arcsec south of IRc2. It might be related to a local bipolar source recently found there in SiO. The jet has very narrow width (not greater than 8 arcsec) and shows no sign of angular divergence; its axis is a straight line. The matter is accelerated all along, with the largest accelerations observed on the central axis. Lower velocity material envelops the high-speed core. Halfway along the jet, there is a sharp break at which the higher velocities terminate abruptly. Beyond the break, acceleration continues without change of direction or strength; the flow's final disappearance might be caused by accelerative dilution. The jet is probably denser than the ambient cloud; its temperature (about 45 K) approaches ambient values. Blueshifted emission of narrow lateral extent is seen over the full length of the redshifted jet.