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)

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions 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! Pudritz & Banerjee 2005

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions Zeeman Splitting “splitting of a spectral line into several components in the presence of a static magnetic field”spectral line magnetic field B=0 B≠0 Circular polarization, V ∝ dI/dv Not not for all masers!

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions SF Masers Maser polarization observed from: OH (1.6 and 6 GHz) Faraday rotation H 2 O (22 GHz) Shocks SiO (43 and 86 GHz) rare, polarization interpretation CH 3 OH (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.

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions Methanol Masers Non-paramagnetic: Zeeman splitting << doppler line-width Using g-Landé factor from 25 GHz laboratory measurements (Jen 1951) : V z = 49 m/s G -1 for 6.7 GHz methanol Circular polarization ~ % 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

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions 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.)

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions Results (I) Cepheus A

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions Survey Results (II) Significant Zeeman splitting detected in 35/ GHz methanol maser sources associated with high-mass star formation Corresponds to |B|=23 ± 5 mG in the methanol region (n H2 ~ cm -3 ) Larger than B crit ~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?

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions 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 W75N (Surcis et al. 2010) 1000 AU

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions 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)

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions Cepheus A results MERLIN image of the polarization of methanol masers around the outflow Cepheus A HW2 750 AU

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions Cepheus A B-field Vlemmings et al. 2010

IntroductionMaser PolarizationEffelsberg survey(e-)MERLINConclusions e-MERLIN MSF legacy project Upgrade to MERLIN array 4 GHz bandwidth, L,C and K- band, ~1 μJy sensitivity, 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 NGC 7538 IRS1 and associated masers (VLA, Galván-Madrid et al. 2010) e-MERLIN beam

IntroductionMaser PolarizationEffelsberg survey(e-)MERLIN Conclusions Significant Zeeman splitting detected in 35/ GHz methanol maser sources associated with high-mass star formation Corresponds to |B|=23 ± 5 mG in the methanol region (n H2 ~ cm -3 ) Larger than B crit ~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