A near-infrared imaging survey of intermediate and high-mass young stellar object outflow candidates
European Southern Observatory, Karl-Schwarschild-Strasse, 2, 85748 Garching, Germany, sramsay@eso.org
Joint Astronomy Centre, 660, N.A’ohuku Place, Hilo, HI 96720, USA
Joint Astronomy Centre, 660, N.A’ohuku Place, Hilo, HI 96720, USA
UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK.
Abstract
We present a new near-infrared imaging survey of 50 luminous young stellar outflow candidates. Using high spatial resolution observations in the v=1-0 S(1) line of H2 we detect the outflows with a high success rate: 76% of the objects exhibit H2 emission and 50% or more of the objects exhibit aligned H2 emission features suggesting collimated outflows. Many of these are new detections. The young stellar objects responsible for the outflows are positively identified in many of our images based on their locations with respect to the outflow lobes, 2MASS colours and association with MSX, IRAS, millimetre and radio sources. The main results of our survey are as follows. The observations suggest that disk accretion is probably the leading mechanism in the formation of stars, at least up to late O spectral types. The close association of molecular outflows detected in CO with the H2 emission features produced by shock excitation by jets from the young stellar objects suggests that the outflows from these objects are jet-driven. Towards strong radio emitting sources, H2 jets were either not detected or were weak when detected, implying that most of the accretion happens in the pre-UCHII phase; accretion and outflows are probably weak when the YSO has advanced to its UCHII stage.