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The Incredible 6.7 GHz Methanol Masers: A key to understanding high-mass star formation.

Image credit: Robert Hurt (NASA/JPL, IPAC/SSC). MAGMO. The Incredible 6.7 GHz Methanol Masers: A key to understanding high-mass star formation. Jimi Green CSIRO Astronomy & Space Science, ATNF Great Barriers in Massive Star Formation 16 th September 2010, Townsville. THE MAGMO TEAM.

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The Incredible 6.7 GHz Methanol Masers: A key to understanding high-mass star formation.

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  1. Image credit: Robert Hurt (NASA/JPL, IPAC/SSC) MAGMO The Incredible 6.7 GHz Methanol Masers:A key to understanding high-mass star formation. Jimi Green CSIRO Astronomy & Space Science, ATNF Great Barriers in Massive Star Formation 16th September 2010, Townsville

  2. THE MAGMO TEAM J. Green, N. McClure-Griffiths, J. L. Caswell, L. Harvey-Smith, T. Robishaw • Plus the Methanol mUltibeam team

  3. Introduction MAGMO is a project to examine large scale magnetic fields pervading regions of high-mass star formation (HMSF). • AIM: • To test whether or not the orientations of weak large-scale magnetic fields can be maintained in the contraction (and field amplification) to the high densities of HMSF. • HOW: • the Zeeman splitting of the OH maser emission will determine the strength and orientation of the in-situ magnetic field. • Correlation of targeted observations of ground-state OH maser emission towards hundreds of sites of HMSF spread throughout the spiral arms of the Galaxy.

  4. OH masers • OH masers are seen in a range of environments from star formation to late type stars and supernova remnants. • Ground-state transitions: • Mainline: 1665 MHz & 1667 MHz • Satellite: 1612 MHz & 1720 MHz • Studying linear polarisation is complicated by Faraday rotation. • However, Zeeman splitting factors for OH masers (Heiles et al. 1993): • 1665 MHz: 0.590 kms-1 mG-1 • 1667 MHz: 0.354 kms-1 mG-1 • Typical field strengths are of the level of a few mG. • => Typical linewidths of 1-2 kms-1 • => Clearlyseparated Zeeman pairs • Zeeman splitting enables us to determine the strength and line-of-sight direction of the in-situ magnetic fields.

  5. Conservation of magnetic field direction? Within regions of high-mass star formation: • masers typically exhibit consistent line-of-sight field directions with comparable field strengths (e.g. Fish & Reid 2007, Nammahachak et al. 2006, Caswell et al. 2010, Vlemmings et al. 2010)

  6. Conservation of magnetic field direction? • On Galactic scales: • Davies (1974) first suggestion of coherent fields across 8 sites. • Reid & Silverstein (1990) coherence over a few kpc for 17 sites. • Fish et al. (2003) coherence in 2nd & 3rd quadrants, and locally in 1st and 4th and levels up to 80% in the spiral arms (about 40 sites observed in study plus previous). • Han & Zhang 2007 compilation. Davies 1974 Reid & Silverstein 1990 Fish et al. 2003

  7. THE PROJECT • Observe 100s of sites in one survey • Methanol Multibeam followup: • With Methanol Multibeam catalogue as targets, can increase previous magnetic field studies by an order of magnitude. • Methanol Multibeam survey detected nearly 1000 sites of 6.7-GHz maser emission (Green et al. 2009, Caswell et al. 2010). • Approximately 80% of ground-state OH maser sites are known to have associated 6.7-GHz methanol (Caswell, 1998). The MMB collaboration: J. L. Caswell, G. A. Fuller, J. A. Green, A. Avison, S. Breen, K. Brooks, M. G. Burton, A. Chrysostomou, J. Cox, P. J. Diamond, S. Ellingsen, M. D. Gray, M. G. Hoare, M. R. W. Masheder, N. McClure-Griffiths, M. Pestalozzi, C. Phillips, L. Quinn, M. Thompson, M. Voronkov, A. Walsh, D. Ward-Thompson, D. Wong-McSweeney, J. A. Yates and R. J. Cohen.

  8. The Plan • observe all 4 ground-state OH transitions using the new broadband backend on the Australia Telescope Compact Array (1612, 1665, 1667 and 1720 MHz) • 8 tunable `zoom’ bands of 1 MHz width with 2048 channels. • Spectral resolution of 0.088 kms-1 • Full `zoom’ capability will enable us to simultaneously observe HI absorption at 1420-MHz, indicative of the cold neutral medium. • 6 km array configuration => ~7 arcsec synthesized beam • `snapshot’ mode with 4/5 cuts across 12 hr period, typically 30-60mins on source • Typical rms of channel maps 25-50 mJy (target is ≤50 mJy) • Positional accuracy of ~0.4 arcsec • Follow-up new sources with VLBI observations with the Australian Long Baseline Array (LBA) to establish Zeeman pairs in complex regions.

  9. A PILOT SAMPLE: The 3 kpc Arms Mulder & Liem. 1986 Expanding Ring Ellipse Grey contours CO 1-0 emission of Dame & Thaddeus 2008

  10. OH in THE 3 kpc arms • Observed the 45 6.7-GHz methanol masers in the 3 kpc arms. • Preliminary results show 29 OH maser detections, 14 lying in the far 3 kpc arm, 15 in the near 3 kpc arm. • 14 of the 29 are new detections. • Median peak flux density of 1.1 Jy (new sources median of 0.7 Jy). • 5 sources with readily identifiable Zeeman pairs indicating in situ magnetic field strengths between 2.1 and 9.0 mG. I,Q,U,V L,R

  11. MASER EMISSION in the 3 kpc arms • Estimate ~40-50% of 6.7-GHz methanol will have associated OH. • Association of OH implies a late stage of high-mass star formation (e.g. Ellingsen 2007, Breen et al. 2010). • Of the 45 methanol sources in the 3-kpc arms we detect OH emission (to within 2 arcsec) in 17 of them, an association of 38%. • Comparison of 3-kpc OH with other maser species: • 6/29 have 6-GHz excited-state OH • 17/29 have 6.7-GHz methanol • 4/29 12 GHz methanol (more to come from MMB followup?) • 14/29 have 22-GHz water (more to come from MMB followup?) Breen et al. 2010

  12. Across the Galaxy and VLBI FOLLOWUP • Distances and Galactic structure • Galactic structure through the longitude-velocity domain • Kinematic distances through maser parallax refined models (Reid et al. 2009, Schoenrich et al. 2010, Bovy et al. 2010) • HI self absorption and association with existing distance catalogues to resolve kinematic distance ambiguities • Maser parallax observations with VLBI for accurate (≤10% error) distances (20 exist, 100s of northern in progress, ~30 southern planned)

  13. Summary • MAGMO is a project to observe the ~1000 Methanol Multibeam sources in all four ground-state transitions of OH. • Through a combination of ATCA and LBA observations, we will explore the concept of conservation of magnetic field direction. • Observations will complement excited-state OH, water and other methanol transition follow-up programmes, helping to determine the evolutionary phase of sites. • Pilot study of 3-kpc arms has detected 29 sources, 14 of which are new detections, suggesting we will double known population. • Large-scale observations start soon, ~500 targets from the Methanol Multibeam survey will be observed in January 2011, remaining ~500 towards end of year. • GASKAP – unbiased Galactic plane survey for OH masers using Australian SKA Pathfinder.

  14. CSIRO Astronomy & Space-Science, ATNF Jimi Green James.green@csiro.au Thank you

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