J/A+A/623/A130 6.7GHz methanol maser polarization in MSFRs IV (Surcis+, 2019)
EVN observations of 6.7 GHz methanol maser polarization in massive star-forming
regions.
IV. Magnetic field strength limits and structure for 7 additional sources.
Surcis G., Vlemmings W.H.T., van Langevelde H.J., Hutawarakorn Kramer B.,
Bartkiewicz A.
<Astron. Astrophys. 623, A130 (2019)>
=2019A&A...623A.130S 2019A&A...623A.130S (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Masers ; Polarization ; Magnetic fields
Keywords: stars: formation - masers - polarization - magnetic fields
Abstract:
Magnetohydrodynamical simulations show that the magnetic field can
drive molecular outflows during the formation of massive protostars.
The best probe to observationally measure both the morphology and the
strength of this magnetic field at scales of 10-100au is maser
polarization.
Measuring the direction of magnetic fields at milliarcsecond
resolution around a sample of massive star forming regions to
determine whether there exists a relation between the orientation of
the magnetic field and of the outflows. In addition by estimating the
magnetic field strength via the Zeeman splitting measurements, the
role of magnetic field in the dynamics of the massive star-forming
region is investigated.
We selected a flux-limited sample of 31 massive star-forming regions
to perform a statistical analysis of the magnetic field properties
with respect to the molecular outflows characteristics. We report the
linearly and circularly polarized emission of 6.7GHz CH3OH masers
towards seven massive star-forming regions of the total sample with
the European VLBI Network. The sources are: G23.44-0.18, G25.83-0.18,
G25.71-0.04, G28.31-0.39, G28.83-0.25, G29.96-0.02, and G43.80-0.13.
We identified a total of 219 CH3OH maser features, 47 and 2 of
which showed linearly and circularly polarized emission, respectively.
We measured well ordered linear polarization vectors around all the
massive young stellar objects and Zeeman splitting towards G25.71-0.04
and G28.83-0.25. Thanks to recent theoretical results, we were able to
provide lower limits to the magnetic field strength from our Zeeman
splitting measurements.
We further confirm (based on ∼80% of the total flux-limited sample)
that the magnetic field on scales of 10-100 au is preferentially
oriented along the outflow axes. The estimated magnetic field strength
of |B|||>61mG and >21mG towards G25.71-0.04 and G28.83-0.2,
respectively, indicates that it dominates the dynamics of the gas in
both regions.
Description:
Seven additional massive SFRs were observed at 6.7GHz in full
polarization spectral mode with with eight of the EVN antennas (Ef,
Jb, On, Mc, Nt, Tr, Wb, and Ys) between March and June 2014. The total
observing time was 49h. We covered a velocity range of ∼100km/s
by observing a bandwidth of 2 MHz. For each observed massive
star-forming region we list all the detected 6.7 GHz CH3OH maser
features with their associated region (when available), relative
position, the peak flux density, the LSR velocity (Vlsr), and the
FWHM (ΔvL) of the total intensity spectra, the mean linear
polarization fraction (Pl) and angles, the outcomes of the adapted
Full Radiative Transfer Method code with errors, the circular
polarization fraction (PV), the Zeeman splitting (ΔVZ),
and the lower limit of the magnetic field strength along the line of
sight.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 131 61 Parameters of the 6.7GHz CH3OH maser features
detected in G23.44-0.18
tablea2.dat 131 46 Parameters of the 6.7GHz CH3OH maser features
detected in G25.83-0.18
tablea3.dat 131 26 Parameters of the 6.7GHz CH3OH maser features
detected in G25.71-0.04
tablea4.dat 131 13 Parameters of the 6.7GHz CH3OH maser features
detected in G28.31-0.39
tablea5.dat 131 21 Parameters of the 6.7GHz CH3OH maser features
detected in G28.83-0.25
tablea6.dat 131 34 Parameters of the 6.7GHz CH3OH maser features
detected in G29.96-0.02
tablea7.dat 131 18 Parameters of the 6.7GHz CH3OH maser features
detected in G43.80-0.13
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See also:
J/A+A/578/A102 : 6.7GHz methanol maser polarization in SFR (Surcis+, 2015)
Byte-by-byte Description of file: tablea?.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Maser Maser name (GLL.ll+B.bb)
11- 13 A3 --- Region Associated Region (only in tablea1.dat)
15- 22 F8.3 mas oRA Offset in right ascension (1)
24- 34 F11.4 mas oDE Offset in declination (1)
36- 41 F6.3 Jy/beam Speak Peak flux density
43- 47 F5.3 Jy/beam e_Speak rms uncertainty on peak flux density
49- 54 F6.2 km/s Vlsr LSR velocity
56- 59 F4.2 km/s FWHM FWHM of the total intensity spectrum
(δVlsr)
61- 64 F4.1 % Pl ?=- Mean value of the linear polarization
fraction measured across the spectrum
66- 68 F3.1 % e_Pl ?=- rms uncertainty on Pl
70- 74 F5.1 deg chi ?=- Mean value of the linear polarization
angle measured across the spectrum
76- 79 F4.1 deg e_chi ?=- rms uncertainty on chi
81 A1 --- l_dVi Limit flag on dVi
82- 84 F3.1 km/s dVi ?=- Intrinsic thermal linewidth (ΔVi)
86- 88 F3.1 km/s E_dVi ? Error on dVi (upper value)
90- 92 F3.1 km/s e_dVi ? Error on dVi (lower value)
94- 97 F4.1 [K/sr] logTbe ?=- Emerging brightness temperature
(logTbΔΩ) (2)
99-101 F3.1 [K/sr] E_logTbe ? Error on logTbe (upper value)
103-105 F3.1 [K/sr] e_logTbe ? Error on logTbe (lower value)
107-109 F3.1 % PV ?=- Circular polarization fraction
111-114 F4.1 m/s dVZ ?=- Zeeman splitting (ΔVZ)
116-118 F3.1 m/s e_dVZ ? rms uncertainty on dVZ
119 A1 --- n_dVZ [e] Note on dVZ (4)
120 A1 --- l_Bper Limit flag on Bper
121-122 I2 mG Bper ?=- Perpendicular magnetic field
123 A1 --- n_Bper [e] Note on Bper (4)
124-125 I2 deg theta ?=- Angle between the magnetic field and
the maser propagation direction (3)
127-128 I2 deg E_theta ? Error on theta (upper value)
129 A1 --- --- [-]
130-131 I2 deg e_theta ? Error on theta (lower value)
--------------------------------------------------------------------------------
Note (1): The reference position is
tablea1.dat (G23.44-0.18): RA=18:34:39.187 and DE=-08:31:25.441 (J2000)
tablea2.dat (G25.83-0.18): RA=18:39:03.630 and DE=-06:24:11.163 (J2000)
tablea3.dat (G25.71-0.04): RA=18:38:03.140 and DE=-06:24:15.453 (J2000)
tablea4.dat (G28.31-0.39): RA=18:44:22.030 and DE=-04:17:38.304 (J2000)
tablea5.dat (G28.83-0.25): RA=18:44:51.080 and DE=-03:45:48.494 (J2000)
tablea6.dat (G29.96-0.02): RA=18:46:03.740 and DE=-02:39:22.299 (J2000)
tablea7.dat (G43.80-0.13): RA=19:11:53.990 and DE=+09:35:50.300 (J2000)
Note (2): The best-fitting results obtained by using a model based on the
radiative transfer theory of methanol masers for
Γ+Γν=1s-1 (Vlemmings et al., 2010MNRAS.404..134V 2010MNRAS.404..134V,
Surcis et al., 2011A&A...533A..47S 2011A&A...533A..47S). The errors were determined by
analyzing the full probability distribution function.
Note (3): The angle between the magnetic field and the maser propagation
direction is determined by using the observed Pl and the fitted emerging
brightness temperature. The errors were determined by analyzing the full
probability distribution function.
Note (4): To model the circularly polarized emission we considered the
error-weighted values of <Tbe≥9.4*108K.sr and DVi=1.1km/s that
best fit the total intensity emission.
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Acknowledgements:
Gabriele Surcis, gabriele.surcis(at)inaf.it
References:
Surcis et al., Paper I 2012A&A...541A..47S 2012A&A...541A..47S
Surcis et al., Paper II 2013A&A...556A..73S 2013A&A...556A..73S
Surcis et al., Paper III 2015A&A...578A.102S 2015A&A...578A.102S, Cat. J/A+A/578/A102
(End) Patricia Vannier [CDS] 08-Feb-2019