EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

Surcis, G.; Vlemmings, Wouter; Langevelde, H. J. van; Kramer, B. Hutawarakorn; Bartkiewicz, A.

doi:10.1051/0004-6361/201834578

Cited by 7 publications

(18 citation statements)

References 94 publications

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“…Since the size of the masing region or the maser beaming angle ∆Ω are often unknown, for comparison with our models, we give the value of the brightness temperature, T B , assuming a maser spot size of 3 mas. We also give a lower limit for T B , based on the observations from Breen et al (2019), Sarma & Momjian (2020), Momjian & Sarma (2019), Surcis et al (2009Surcis et al ( , 2019. In the case of the 12.2 GHz maser, we did not model a specific source but we give a typical value on the basis of the previous work by Moscadelli et al (2003).…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, the change of magnetic field direction along the maser propagation direction can contribute at most ∼0.04%, that is only a fraction of the observed values of P V (e.g. Surcis et al 2009Surcis et al , 2012Surcis et al , 2019. However, this effect can be important for very high levels of linear polarisation P L ∼ 10%, causing an extra P V ∼ 0.25%.…”

Section: Effect Of Magnetic Field Changesmentioning

confidence: 96%

“…(b) From Breen et al (2019). (c) For W3(OH) we refer to the feature W3OH.22 from Surcis et al (2019), and for W75N to Surcis et al (2009). (d) We do not model any specific maser but we only report values observed by Moscadelli et al (2003).…”

Section: 7 Ghz Methanol Masermentioning

confidence: 99%

“…We compared the results of our simulations with 6.7 GHz maser observations from Breen et al (2019), and Surcis et al (2019Surcis et al ( , 2009; these masers are reported in Table 1. These works reported high P L on the order of 7.5, 8.1, and 4.5% respectively.…”

Section: 7 Ghz Methanol Masersmentioning

confidence: 99%

“…In particular, methanol masers have emerged as excellent tools for probing magnetic fields during star formation (e.g. Vlemmings 2008;Surcis et al 2019;Momjian & Sarma 2019;Sarma & Momjian 2020, and references therein). Although the circularly polarised emission of methanol maser has been regularly detected, no exact estimates of the magnetic field strength have been possible due to the fact that the Landé g-factors were previously unknown (Vlemmings et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Polarisation properties of methanol masers

Dall'Olio

Vlemmings

Lankhaar

et al. 2020

A&A

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Context. Astronomical masers have been effective tools in the study of magnetic fields for years. Observations of the linear and circular polarisation of different maser species allow for the determination of magnetic field properties, such as morphology and strength. In particular, methanol can be used to probe different parts of protostars, such as accretion discs and outflows, since it produces one of the strongest and the most commonly observed masers in massive star-forming regions. Aims. We investigate the polarisation properties of selected methanol maser transitions in light of newly calculated methanol Landé g-factors and in consideration of hyperfine components. We compare our results with previous observations and evaluate the effect of preferred hyperfine pumping and non-Zeeman effects. Methods. We ran simulations using the radiative transfer code, CHAMP, for different magnetic field values, hyperfine components, and pumping efficiencies. Results. We find a dependence between the linear polarisation fraction and the magnetic field strength as well as the hyperfine transitions. The circular polarisation fraction also shows a dependence on the hyperfine transitions. Preferred hyperfine pumping can explain some high levels of linear and circular polarisation and some of the peculiar features seen in the S-shape of observed V-profiles. By comparing a number of methanol maser observations taken from the literature with our simulations, we find that the observed methanol masers are not significantly affected by non-Zeeman effects related to the competition between stimulated emission rates and Zeeman rates, such as the rotation of the symmetry axis. We also consider the relevance of other non-Zeeman effects that are likely to be at work for modest saturation levels, such as the effect of magnetic field changes along the maser path and anisotropic resonant scattering. Conclusions. Our models show that for methanol maser emission, both the linear and circular polarisation percentages depend on which hyperfine transition is masing and the degree to which it is being pumped. Since non-Zeeman effects become more relevant at high values of brightness temperatures, it is important to obtain good estimates of these quantities and the maser beaming angles. Better constraints on the brightness temperature will help improve our understanding of the extent to which non-Zeeman effects contribute to the observed polarisation percentages. In order to detect separate hyperfine components, an intrinsic thermal line width that is significantly smaller than the hyperfine separation is required.

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Section: Methodsmentioning

confidence: 99%

Section: Effect Of Magnetic Field Changesmentioning

confidence: 96%

Section: 7 Ghz Methanol Masermentioning

confidence: 99%

Section: 7 Ghz Methanol Masersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Polarisation properties of methanol masers

Dall'Olio

Vlemmings

Lankhaar

et al. 2020

A&A

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Laboratory disruption of scaled astrophysical outflows by a misaligned magnetic field

et al. 2021

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The shaping of astrophysical outflows into bright, dense, and collimated jets due to magnetic pressure is here investigated using laboratory experiments. Here we look at the impact on jet collimation of a misalignment between the outflow, as it stems from the source, and the magnetic field. For small misalignments, a magnetic nozzle forms and redirects the outflow in a collimated jet. For growing misalignments, this nozzle becomes increasingly asymmetric, disrupting jet formation. Our results thus suggest outflow/magnetic field misalignment to be a plausible key process regulating jet collimation in a variety of objects from our Sun’s outflows to extragalatic jets. Furthermore, they provide a possible interpretation for the observed structuring of astrophysical jets. Jet modulation could be interpreted as the signature of changes over time in the outflow/ambient field angle, and the change in the direction of the jet could be the signature of changes in the direction of the ambient field.

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EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

Surcis

Vlemmings

Langevelde

et al. 2022

A&A

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Context. Although the role of magnetic fields in launching molecular outflows in massive young stellar objects has been convincingly demonstrated by theoretical arguments, observationally, the alignment of the magnetic field lines with the molecular outflows is still under debate. Aims. We aim to complete the measurements of the direction of the magnetic fields at milliarcsecond resolution around a sample of massive star-forming regions to determine whether the magnetic field and outflows are aligned. Methods. In 2012, we started a large very long baseline interferometry campaign with the European VLBI Network to measure the magnetic field orientation and strength toward a sample of 31 massive star-forming regions (called the flux-limited sample) by analyzing the polarized emission of 6.7 GHz CH3OH masers. In the previous papers of the series, we have presented 80% of the sample. Here, we report the linearly and circularly polarized emission of 6.7 GHz CH3OH masers toward the last five massive star-forming regions of the flux-limited sample. The sources are G30.70-0.07, G30.76-0.05, G31.28+0.06, G32.03+0.06, and G69.52-0.97. Results. We detected a total of 209 CH3OH maser cloudlets, 15% of which show linearly polarized emission (0.07–16.7%), and 2% of which show circularly polarized emission (0.2–4.2%). As reported in previous papers, in the last five sources of the flux-limited sample, we also measured well-ordered linear polarization vectors. Zeeman splitting was measured toward G30.70-0.07, G32.03+0.06, and G69.52-0.97. Conclusions. The statistical analysis of the entire flux-limited sample shows that the observations are consistent with a bimodal distribution in the difference between the 3D magnetic field direction and the outflow axis, with half the magnetic field directions being perpendicular and the other half being parallel to the outflow. In addition, we determined that typical values of the linear and circular polarization fractions for 6.7 GHz CH3OH masers are Pl = 1.0–2.5% and PV = 0.5–0.75%, respectively. From the circularly polarized spectra of the CH3OH maser features, we found that a typical Zeeman splitting is in the range between 0.5 m s−1 and 2.0 m s−1. This would correspond to 9 mG < |B||| < 40 mG if F = 3 → 4 is the most favored of the eight hyperfine transitions that might contribute to the maser emission.

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EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

Cited by 7 publications

References 94 publications

Polarisation properties of methanol masers

Polarisation properties of methanol masers

Laboratory disruption of scaled astrophysical outflows by a misaligned magnetic field

EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

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