J/MNRAS/510/6085 Magnetic field of Taurus/B211 (Li+, 2022)
Mapping the magnetic field in the Taurus/B211 filamentary cloud with
SOFIA HAWC+ and comparing with simulation.
Li P.S., Lopez-Rodriguez E., Ajeddig H., Andre P., McKee C.F., Rho, J.,
Klein, R.I.
<Mon. Not. R. Astron. Soc. 510, 6085-6109 (2022)>
=2022MNRAS.510.6085L 2022MNRAS.510.6085L (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Magnetic fields ; Polarization
Keywords: methods: numerical - techniques: polarimetric - ISM: clouds -
ISM: kinematics and dynamics - ISM: magnetic fields - ISM: structure
Abstract:
Optical and infrared polarization mapping and recent Planck
observations of the filamentary cloud L1495 in Taurus show that the
large-scale magnetic field is approximately perpendicular to the long
axis of the cloud. We use the HAWC+ polarimeter on SOFIA to probe the
complex magnetic field in the B211 part of the cloud. Our results
reveal a dispersion of polarization angles of 36°, about five
times that measured on a larger scale by Planck. Applying the
Davis-Chandrasekhar-Fermi (DCF) method with velocity information
obtained from IRAM 30m C18O(1-0) observations, we find two distinct
sub-regions with magnetic field strengths differing by more than a
factor 3. The quieter sub-region is magnetically critical and
sub-Alfvenic; the field is comparable to the average field measured in
molecular clumps based on Zeeman observations. The more chaotic,
super-Alfvenic sub-region shows at least three velocity components,
indicating interaction among multiple substructures. Its field is much
less than the average Zeeman field in molecular clumps, suggesting
that the DCF value of the field there may be an underestimate.
Numerical simulation of filamentary cloud formation shows that
filamentary substructures can strongly perturb the magnetic field. DCF
and true field values in the simulation are compared. Pre-stellar
cores are observed in B211 and are seen in our simulation. The
appendices give a derivation of the standard DCF method that allows
for a dispersion in polarization angles that is not small, present an
alternate derivation of the structure function version of the DCF
method, and treat fragmentation of filaments.
Description:
FITS file of the HAWC+ observations at 214 microns with an angular
resolution of 28.1 arcseconds.
Objects:
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RA (2000) DE Designation(s)
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04 18.1 +27 37 L1495 = LDN 1495
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 140 18 Infornations on fits extension of the FITS file
fits/* . 1 FITS file
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg ? Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg ? Declination of center (J2000)
20- 21 I2 --- Nx Number of pixels along X-axis
23- 26 I4 --- Ny Number of pixels along Y-axis
28- 50 A23 "datime" Obs.date Observation date
52- 53 I2 --- HDU [0/17] Extension number (1)
55- 57 I3 Kibyte size Size of FITS file
59- 68 A10 --- FileName Name of FITS file, in subdirectory fits
70-140 A71 --- Title Title of the FITS file extension
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Note (1): Note for tables.
HDU 17: Polarization data for each pixel
table representation of the degree, polarization, and debiased polarization
maps in extensions 7-12 for every pixel in both x,y and ra,dec coordinates.
(see next table, HDU 18)
HDU 18: Subset of POL DATA with quality cuts
FINAL POL DATA is a quality cut of POL DATA for all pixels with
I/sigmaI≥200, p/sigmap≥3, and p<50%.
Description of HDU 17 (POL DATA)
-------------------------------------------------------------------------------
Column name Units Explanations
-------------------------------------------------------------------------------
Pixel X pix X pixel coordinates
Pixel Y pix Y pixel coordinates
Right Ascension deg Right ascension (J2000.0)
Declination deg Declination (J2000.0)
Debiased Percent Pol % Polarization percent, extension 7 (PERCENT POL)
Err. Percent Pol % Debiased polarization percent, extension 8
(DEBIASED PERCENT POL)
Theta deg Polarization angle in sky coordinates,
extension 10 (POL ANGLE)
Rotated Theta deg Polarization angle rotated by 90 deg.,
extension 11 (ROTATED POL ANGLE)
Err. Theta deg Error in theta,
extension 12 (ERROR POL ANGLE)
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Acknowledgements:
Pak Shing Li, psli(at)berkeley.edu
(End) Patricia Vannier [CDS] 26-Nov-2021