We present CO(2-1), 13CO(2-1), CO(6-5),CO(7-6), and SO(65-54)lineobservations made with the IRAM 30m and Atacama PathfinderExperiment (APEX) radiotelescopes and the SubmillimeterArray (SMA) toward the highly collimated(11)and extended (2')southwest lobe of the bipolar outflow Ori-S6located in the Orion South region. We report for all these lines, thedetection of velocity asymmetries about the flow axis with velocitydifferences roughly on the order of 1kms-1over distances of about 5000AU, 4kms-1over distances of about 2000AU, and close to the source ofbetween7 and 11kms-1over smaller scales of about 1000AU. The redshifted gasvelocities are located to the southeast of the outflow's axis, theblueshifted ones to the northwest. We interpret these velocitydifferences as a signature of rotation, but also discuss somealternatives which we recognize as unlikely in view of the asymmetries'large downstream continuation. Inparticular, anystraightforward interpretation by an ambient velocity gradient does notseem viable. This rotation across the Ori-S6outflowis observed out to (projected) distances beyond 2.5104AU from the flow's presumed origin.Comparison of our large-scale (single dish) and small-scale (SMA)observations suggests the rotational velocity todecline not faster than 1/R with distanceRfrom the axis; in the innermost few arcsecs an increase of rotationalvelocity withR is even indicated. Themagnetic field lines threading the inner rotating COshell maywell be anchored in a disk of a radius of 50AU; the fieldlines further out need a more extended rotating base. Our high angularresolution SMA observations also suggest this outflow to be energizedby the compact millimeter radio source139-409,acircumbinary flattened ring that is located in a smallcluster of very young stars associated with the extended and brightsourceFIR4.Key words: ISM: jets and outflows -techniques: high angular resolution - binaries: general - stars:pre-main sequence - ISM: molecules - radio lines: ISM
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