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Masers observations of Magnetic fields during Massive Star Formation

Masers observations of Magnetic fields during Massive Star Formation. Wouter Vlemmings (Argelander-Institut für Astronomie, Bonn) with Gabriele Surcis, Rosy Torres, Ramiro Franco (Bonn) Kalle Torstensson, Huib Jan van Langevelde (Leiden/JIVE, Netherlands), Richard Dodson (ICRAR, Australia).

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Masers observations of Magnetic fields during Massive Star Formation

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  1. Masers observations of Magnetic fields during Massive Star Formation • Wouter Vlemmings(Argelander-Institut für Astronomie, Bonn) • with Gabriele Surcis, Rosy Torres, Ramiro Franco (Bonn) Kalle Torstensson, Huib Jan van Langevelde (Leiden/JIVE, Netherlands), Richard Dodson (ICRAR, Australia)

  2. Pudritz & Banerjee 2005 MSF Magnetic Fields • Role relative to turbulence and gravity? • B launches outflows, stabilize accretion disks, facilitate enhanced accretion rate? • B suppresses fragmentation? • Need B-field probes at high densities and small scales • complement larger scale dust • Zeeman splitting of masers and other spectral lines!

  3. Zeeman Splitting • “splitting of a spectral line into several components in the presence of a static magnetic field” B=0 B≠0 • Circular polarization, V∝dI/dv • Not not for all masers!

  4. SF Masers • Maser polarization observed from: • OH (1.6 and 6 GHz) • Faraday rotation • H2O (22 GHz) • Shocks • SiO (43 and 86 GHz) • rare, polarization interpretation • CH3OH (methanol, 6.7, 12.2, 36 GHz) • Common MSF maser, strong Poster I.24, Green et al. & II.32 Torres et al. Poster II.26, Surcis et al. Poster II.26, Surcis et al.

  5. Methanol Masers • Non-paramagnetic: • Zeeman splitting << doppler line-width • Using g-Landé factor from 25 GHz laboratory measurements (Jen 1951): • Vz = 49 m/s G-1 for 6.7 GHz methanol • Circular polarization ~0.1-0.3% for mG B-fields • Linear polarization weak (Ellingsen 2002; Vlemmings et al. 2006; Dodson 2008) • Typical 2-3% for 6.7 and 12.2 GHz masers • Occasionally as high as 8-10% • Depends on e.g. maser saturation • Analysis requires maser radiative transfer

  6. Effelsberg survey • Detection of Zeeman splitting requires high SNR • SNR~3000 needed to detect 1 mG • Strong masers (>50Jy) • Effelsberg 100m telescope: • 51 hr; ~50 strong Northern methanol maser regions • Southern sources done with Parkes MB system • Stability problem, scan-to-scan Right-Left CP variability • Still simultaneous 6 GHz OH (poster II.32, Torres et al.)

  7. Results (I) Cepheus A

  8. Survey Results (II) • Significant Zeeman splitting detected in 35/47 6.7 GHz methanol maser sources associated with high-mass star formation • Corresponds to |B|=23 ± 5 mG in the methanol region (nH2~107-109 cm-3) • Larger than Bcrit~12 mG ⇒ dynamically important • Average field ~6 times higher than average 1.6 GHz OH maser field • Line-of-sight direction consistent with OH maser measurements • Probes overall Galactic field direction?

  9. Further observations • High resolution follow-up (EVN; Surcis poster II.26) • confirmed field • indicate connection to larger scale structure • 6 GHz OH Effelsberg survey • B vs. density relation 1000 AU W75N (Surcis et al. 2010)

  10. The case of Cepheus A • Cepheus A HW2 ~20 M☉ @ 700 pc (Jiménez-Serra et al. 2007; Moscadelli et al. 2009) • Thermal radio jet, ionized gas at ~500 km/s (Curiel et al. 2006) • Rotating dust (R~330 AU) and molecular gas (R~580 AU) disk structure ⊥ to outflow (Patel et al. 2005, Jiménez-Serra et al. 2007, Torrelles et al. 2007) • made up of at least 3 YSOs (e.g. Comito et al. 2007) • Flattened 6.7 GHz methanol maser structure near disk plane (R~650 AU, h~300 AU) • infall at ~1.7 km/s (Torstensson et al. 2007, 2010)

  11. MERLIN image of the polarization of methanol masers around the outflow Cepheus A HW2 750 AU Cepheus A results

  12. Cepheus A B-field Vlemmings et al. 2010

  13. e-MERLIN MSF legacy project • Upgrade to MERLIN array • 4 GHz bandwidth, L,C and K-band, ~1 μJy sensitivity, 10-150 mas resolution • ‘Feedback during Massive Star Formation’ • 450 hrs allocated at C-band (5-7 GHz) • simultaneous map radio continuum emission and the 3D magnetic field from methanol/OH masers e-MERLIN beam NGC 7538 IRS1 and associated masers (VLA, Galván-Madrid et al. 2010)

  14. Conclusions • Significant Zeeman splitting detected in 35/47 6.7 GHz methanol maser sources associated with high-mass star formation • Corresponds to |B|=23 ± 5 mG in the methanol region (nH2~107-109 cm-3) • Larger than Bcrit~12 mG ⇒ dynamically important • Average field ~6 times higher than average 1.6 GHz OH maser field • High-resolution studies show relation with large scale fields • Cepheus A: magnetic field regulated infall

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