J/A+A/614/A100 Molecular clouds los magnetic field structure (Tahani+, 2018)
Helical magnetic fields in molecular clouds? A new method to determine the
line-of-sight magnetic field structure in molecular clouds.
Tahani M., Plume R., Brown J.C., Kainulainen J.
<Astron. Astrophys. 614, A100 (2018)>
=2018A&A...614A.100T 2018A&A...614A.100T (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Magnetic fields
Keywords: methods: observational - ISM: magnetic fields - stars: formation -
magnetic fields
Abstract:
Magnetic fields pervade in the interstellar medium (ISM) and are
believed to be important in the process of star formation, yet probing
magnetic fields in star formation regions is challenging. Aims. We
propose a new method to use Faraday rotation measurements in
small-scale star forming regions to find the direction and magnitude
of the component of magnetic field along the line of sight. We test
the proposed method in four relatively nearby regions of Orion A,
Orion B, Perseus, and California.
We use rotation measure data from the literature. We adopt a simple
approach based on relative measurements to estimate the rotation
measure due to the molecular clouds over the Galactic contribution. We
then use a chemical evolution code along with extinction maps of each
cloud to find the electron column density of the molecular cloud at
the position of each rotation measure data point. Combining the
rotation measures produced by the molecular clouds and the electron
column density, we calculate the line-of-sight magnetic field strength
and direction.
In California and Orion A, we find clear evidence that the magnetic
fields at one side of these filamentary structures are pointing
towards us and are pointing away from us at the other side. Even
though the magnetic fields in Perseus might seem to suggest the same
behavior, not enough data points are available to draw such
conclusions. In Orion B, as well, there are not enough data points
available to detect such behavior. This magnetic field reversal is
consistent with a helical magnetic field morphology. In the vicinity
of available Zeeman measurements in OMC-1, OMC-B, and the dark cloud
Barnard 1, we find magnetic field values of -23±38uG, -129±28uG,
and 32±101uG, respectively, which are in agreement with the Zeeman
measurements.
Description:
We propose a new method to use Faraday rotation measurements in small
scale star forming regions to find the direction and magnitude of the
component of magnetic field along the line-of-sight. We test the
proposed method in four relatively nearby regions of Orion A, Orion B,
California, and Perseus.
Tables 1, 3, 4, and 6 show the result magnetic fields for these
regions.
Tables 2, 5, and 7 show the result magnetic fields that do not change
direction within their uncertainty range for Orion A, California, and
Perseus respectively. Negative values indicate magnetic fields pointed
away from the observer and positive values are towards the observer.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 65 34 Line-of-sight magnetic field in Orion A
table2.dat 65 14 Line-of-sight magnetic field in Orion A (Table 1),
but only points with fixed direction
table3.dat 65 8 Line-of-sight magnetic field in Orion B
table4.dat 65 35 Line-of-sight magnetic field in California
table5.dat 65 15 Line-of-sight magnetic field in California
(Table 4), but only points with fixed direction
table6.dat 65 24 Line-of-sight magnetic field in Perseus
table7.dat 65 11 Line-of-sight magnetic field in Perseus (Table 6),
but only points with fixed direction
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See also:
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
Byte-by-byte Description of file: table?.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Point Point Numbers in the figures 6, 7, 8, 9
5- 9 F5.2 deg RAdeg Right ascension (J2000)
13- 18 F6.2 deg DEdeg Declination (J2000)
21- 25 F5.2 mag AV Extinction in V band
29- 34 F6.1 rad/m2 RMon Rotation measure (1)
37- 42 F6.1 rad/m2 RMmc Rotation measure of Molecular Cloud (2)
46- 50 I5 ugauss Blos Line of sight magnetic field of the Cloud
54- 57 I4 ugauss E_Blos Upper uncertainty of magnetic Field
62- 65 I4 ugauss e_Blos Lower uncertainty of magnetic Field
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Note (1): RMon is the rotation measure obtained from Taylor et al.
(2009, Cat. J/ApJ/702/1230) catalog.
Note (2): RMmc is the rotation measure of the molecular cloud alone,
as explained in the paper.
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Acknowledgements:
Mehrnoosh Tahani, mtahani(at)ucalgary.ca
(End) Mehrnoosh Tahani [Univ. Calgary], Patricia Vannier [CDS] 06-Mar-2018