Masers observations of Magnetic fields during Massive Star Formation Wouter Vlemmings (Argelander-Institut für Astronomie, Bonn) with Gabriele Surcis,

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)

QuickTime™ and a decompressor

are needed to see this picture.



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






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!


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.


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


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.)


Results (I)Cepheus A


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?


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


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)










Cepheus A results

MERLIN image of the polarization of methanol masers around the outflow Cepheus A HW2

750

AU


Cepheus A B-field

QuickTime™ and aGIF decompressor


Vlemmings et al. 2010


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

NGC 7538 IRS1 and associated masers

(VLA, Galván-Madrid et al. 2010)

e-MERLIN beam


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

Documents

Masers observations of Magnetic fields during Massive Star Formation Wouter Vlemmings (Argelander-Institut für Astronomie, Bonn) with Gabriele Surcis,