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Can masers trace the Galactic magnetic field?

Can masers trace the Galactic magnetic field?. The MAGMO Survey. CSIRO ASTRONOMY AND SPACE SCIENCE. Jimi Green | A Neapolitan of Maser Science 2013 | Sydney. 21 st May 2013. Overview Can hydroxyl (OH) masers map the Galactic magnetic field ?. Introduction

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Can masers trace the Galactic magnetic field?

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  1. Can masers trace the Galactic magnetic field? The MAGMO Survey CSIRO ASTRONOMY AND SPACE SCIENCE Jimi Green | A Neapolitan of Maser Science 2013 | Sydney 21st May 2013

  2. Overview Can hydroxyl (OH) masers map the Galactic magnetic field? • Introduction • Zeeman splitting of OH masers • Star formation environment of OH masers • Magnetic fields of OH masers • Description of MAGMO • Aims • Collaborators • Observations • Results from MAGMO • First results of pilot region • Expected full results • Summary MAGMO | Jimi Green | Page 2

  3. Zeeman splitting of OH masers Introduction • Paramagnetic molecule • Large splitting factors for maser transitions • Narrow linewidths (typically <1 kms-1) • Field strengths of the level of a few mG Zeeman splitting enables us to determine: (total) field strength & line-of-sight orientation of the in situ magnetic fields Green et al. 2012 MAGMO | Jimi Green | Page 3

  4. Star formation environment of OH masers Introduction Fish & Reid 2007 • Temperatures: • 30 K to >150 K • H2 densities: • 106 to 107 • OH abundances: • 10s to 100s cm-3 • OH masers lie on edge of Ultra-Compact HII regions (from VLBI) • Large scale magnetic field known from rotation measure observations (e.g. Brown et al. 2007 and van Eck et al. 2011) • Ultra-Compact HII regions known to exhibit orientation of Galactic magnetic field (e.g. Harvey-Smith et al. 2011) + + + + + + ~20 mpc (4000 AU) Image credit: Robert Hurt (NASA/JPL, IPAC/SSC) R. Hurt: NASA/JPL-Caltech/SSC MAGMO | Jimi Green | Page 4

  5. Magnetic fields of OH masers Introduction Fish & Reid 2007 • Temperatures: • 30 K to >150 K • H2 densities: • 106 to 107 • OH abundances: • 10s to 100s cm-3 • Masers typically exhibit consistent line-of-sight magnetic field orientations with comparable field strengths (of a few mG) • Limited scale studies have found coherence of field orientation across multiple sites of star formation, over scales of a few kpc [e.g. Davies 1974 , Reid & Silverstein 1990, Fish et al. 2003, Han & Zhang 2007 compilation] + + + + + + ~20 mpc (4000 AU) van Eck et al. 2011 R. Hurt: NASA/JPL-Caltech/SSC MAGMO | Jimi Green | Page 5

  6. Aims of MAGM Project description • Examine magnetic fields pervading regions of high-mass star formation • Measure Zeeman splitting of OH masers to determine the strength and orientation of the in situ magnetic field • Correlate homogeneous observations of 100s of sites of high-mass star formation spread throughout the spiral arms of the Galaxy • Test if the orientations of weak large-scale magnetic fields can be maintained in the contraction (and field amplification) to the high densities of high-mass star formation MAGMO | Jimi Green | Page 6

  7. Collaborators of MAGM Project description Naomi McClure-Griffiths CSIRO Astronomy & Space Science James Caswell CSIRO Astronomy & Space Science Tim Robishaw NRC-HIA, DRAO Lisa Harvey-Smith CSIRO Astronomy & Space Science Sui Ann Mao University of Wisconsin + Methanol Multibeam Collaboration MAGMO | Jimi Green | Page 7

  8. Observations of MAGM Project description • Targets: 6.7-GHz methanol masers (from Methanol Multibeam survey), exclusive tracers of high-mass star formation • Utilised new broadband backend and 16cm receivers on the Australia Telescope Compact Array (ATCA) • Ground-state OH transitions (1612, 1665, 1667 & 1720 MHz) • Full Stokes polarisation (I, Q, U, V) • 16 tunable ‘zoom’ bands of 1 MHz width with 2048 channels (velocity resolution ~0.1 kms-1) at 2 Intermediate Frequencies. • ~30' primary beam, fitted positional accuracy ~0.4'' • ‘snapshot’ observing mode with 4/5 cuts across 12 hr period, • ~50mJy rms channel noise MAGMO | Jimi Green | Page 8

  9. Carina-Sagittarius Arm Tangent Results (Green et al. 2012, MNRAS, 425, 2530) + 6.7-GHz methanol masers (Green et al. 2012) • 17 sites of OH masers across 6 star forming regions, 11 Zeeman pairs • Coherent magnetic field orientation observed across ~5 kpc of spiral arm • Opposite (!) orientation to that indicated by rotation measures Hα emission (SHASSA, Gaustad et al. 2001) • Carina-Sagittarius • Crux-Scutum • Perseus • Norma MAGMO | Jimi Green | Page 9

  10. Summary of full survey results Results (Green et al. in prep) • Observations completed (~500 hrs between 2010 and 2012) • All 6.7-GHz methanol masers between longitudes 186° and 20° observed • Data reduced through python scripted MIRIAD • ~500 (SF) 1665-MHz OH masers, ~300 1667-MHz • Detection rate implies ~300 Zeeman pair measurements across the Galaxy • Frequent, high % circular polarisation • Infrequent, high % linear polarisation • Coherent field orientations over several kpc => field direction conserved MAGMO | Jimi Green | Page 10

  11. Still to come... Results • Full analysis of in situ arm fields (combining longitude-velocity with astrometric distances) • Zeeman field orientation versus Rotation Measure orientation • VLBI followup results – high resolution Zeeman pair identification • Associated excited-state OH analysis – Zeeman pair confirmation • MAGMO (targeted survey of star formation OH with I,Q,U,V) • GASKAP & SPLASH (blind survey of all OH with I,V) • POSSUM (rotation measure complement) • northern hemisphere survey (& Galactic plane completion) Reid & Silverstein 1990 Davies 1974 van Eck et al. 2011 Fish et al. 2003 Brown et al. 2007 MAGMO ? MAGMO | Jimi Green | Page 11

  12. Still to come... All the extras • VLBI follow-up observations - 4 sources observed with Long Baseline Array (LBA) – Zeeman pairs identifications confirmed • Excited-state OH studies – 30 bright sources observed with Australia Telescope Compact Array with full Stokes polarisation, Pi component identification ~15% of Zeeman pairs • Variability studies – long term, high cadence monitoring similar to G12.889 • HI Self Absorption study – HI observed simultaneously with maser transitions • Masers associated with evolved stars (serendipitous 1612-MHz detections) MAGMO | Jimi Green | Page 12

  13. Thank you • Neapolitan of Maser Science 2013 | Sydney • Jimi GreenThe MAGMO Survey t +61 2 9372 4610 e james.green@csiro.au CSIRO ASTRONOMY AND SPACE SCIENCE

  14. Zeeman splitting Conventions & definitions • Splitting of otherwise degenerate energy levels in presence of magnetic field. • Maser emission seen from transitions between levels. • Three components: σ+, σ-, π. MAGMO | Jimi Green | Extra Page

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