SiO outflow signatures toward massive young stellar objects with linearly distributed methanol masers

¹ SOFIA - USRA, NASA Ames Research Center, MS N211-3, Moffett Field, CA 94035, USA e-mail: jdebuizer@sofia.usra.edu
² Gemini Observatory, Casilla 603, La Serena, Chile
³ National Research Council of Canada, 5071 W. Saanich Rd, Victoria, BC V9E 2E7, Canada
⁴ School of Physics, University of New South Wales, Sydney, 2052 NSW, Australia
⁵ Australia Telescope National Facility, CSIRO, PO Box 76 Epping, NSW 1710, Australia

Received: 3 September 2008
Accepted: 24 October 2008

Abstract

Context. Methanol masers are often found in linear distributions, and it has been hypothesized that these masers trace circumstellar accretion disks around young massive stars. However, recent observations in H₂ emission have shown what appear to be outflows at similar angles to the maser distribution angles, not perpendicular as expected in the maser-disk scenario.

Aims. The main motivation behind the observations presented here is to use presence and morphology of an independent outflow tracer, namely SiO, to determine if there are indeed outflows present in these regions and if they are consistent or inconsistent with the maser-disk hypothesis.

Methods. For ten sources with H₂ emission, we obtained JCMT single-dish SiO (6–5) observations to search for this outflow indicator. We followed up those observations with ATCA interferometric mapping of the SiO emission in the (2–1) line in six sources.

Results. The JCMT observations yielded a detection in the SiO (6–5) line in nine of the ten sources. All of the sources with bright SiO lines display broad line wings indicative of outflow. A subset of the sources observed with the JCMT have methanol maser velocities significantly offset from their parent cloud velocities, supporting the idea that the masers in these sources are likely not to be associated with circumstellar disks. The ATCA maps of the SiO emission show five of the six sources do indeed have SiO outflows (the only non-detection being the same source that was a non-detection in the JCMT observations). The spatial orientations of the outflows are not consistent with the methanol masers delineating disk orientations. Overall, the observations presented here seem to provide further evidence against the hypothesis that linearly distributed methanol masers generally trace the orientations of circumstellar disks around massive young stars.