2005A&A...440..569A

We have searched for optical shock-excited emission lines in the outer parts of the bipolar outflows from massive young stellar objects where the flow terminates and the extinction is expected to be low. The Taurus Tunable Filter (TTF) at the Anglo-Australian Telescope (AAT) was used to obtain narrow-band (12-15Å) images of the Hα, [NII]6583, and [S II]6717/6731 lines around MonR2IRS3, S255IRS1/3, GL961 and GL989. No clear examples of shocked emission were found. A bow shock feature in the GL989 region maybe related with the molecular outflow NGC 2264D. A weak optical bow-like feature is seen in GL961, but which of the stars in the cluster is the driving source cannot be uniquely identified. Other emission line features were found in MonR2 and S255 that are consistent with an HII region origin. The observed fluxes and the upper limits were compared with predictions from radiative shock models available in the literature. Any head-on collisions of a jet with speeds of the order of 500km/s should have been detected if the extinction A_v<10mag. Estimates of the extinction in the outer parts of the molecular clouds are somewhat lower than this, although it is possible that it could be higher local to any interaction regions due to swept up material. If the extinction is low, then the shocks must either be slower (<150km/s) or very oblique (>75°), which would argue against the presence of highly collimated jets from high mass young stellar objects.