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The 6.7-GHz methanol maser in the high mass star forming region G213.70-12.6

Submitter: Maria Grazia Blasi, Gabriele Surcis
Description: The picture shows the results obtained during my summer project at the JIVE Institute, that is the study of the 6.7-GHz methanol maser in the high-mass star-forming region G213.70-12.6 (also known as Monoceros R2 and IRAS06053-0622).
The investigation of the polarized emission of methanol masers in this region allowed us to determine the orientation and the strength of the magnetic field in order to improve our understanding of the role played by the magnetic field during the massive star formation.
The main image shows the distribution of the twenty 6.7-GHz methanol maser features that we detected around G213.70-12.6, which is located at about 830 pc from us. The triangles symbols are the identified maser features scaled logarithmically according to their peak flux. A 5 Jy/beam symbol is plotted for illustration.
The dashed line is the best linear fit of the maser features. The black segments indicate the linear polarization vectors (scaled logarithmically according to the polarization fraction) for the six masers for which we were able to detect linearly polarized emission. The study of the linear polarization is useful for determining the magnetic field orientation, which in this case is perpendicular to the linear polarization vectors (see right bottom corner).

The three images on the bottom show the results obtained for the brightest methanol maser feature (peak flux ~ 91 Jy/beam).
On the most left image we show on the top panel a comparison between the total (black line) and linearly polarized (red line, multiplied by a factor of 3) spectra, while on the bottom panel we show the linear polarization percentage (full line) and the linear polarization angle (dashed line) across the maser emission.
On the middle image we show the result of the full radiative transfer Chi-squared model fit (also known as Full Radiative Transfer Method code, FRTM). The fit yields the emerging brightness temperature and the intrinsic thermal linewidth of the maser. Contours indicate the significance intervals 0.25, 0.5, 1, 2, 3, and 7, with the thick solid contours indicating 1 sigma and 3 sigma areas.
On the right image we show how the model of the methanol maser emission (red line), which was determined by using the best values obtained from the FRTM code, fits the total (I) and the circularly polarized (V) emission of the maser. From this last fit we estimated a Zeeman-splitting of (-7 +/- 1) m/s which indicate a magnetic field on the plane of the sky in the range between 140 mG and 1.4 G depending on the Zeeman-splitting coefficient which is still uncertain for the 6.7-GHz methanol maser emission.
Copyright: Gabriele Surcis, Maria Grazia Blasi
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