J/A+A/690/A314 Disentangling the Faraday rotation sky (Hutschenreuter+, 2024)
Disentangling the Faraday rotation sky.
Hutschenreuter S., Haverkorn M., Frank P., Raycheva N., Ensslin T.
<Astron. Astrophys. 690, A314 (2024)>
=2024A&A...690A.314H 2024A&A...690A.314H (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Models ; Magnetic fields
Keywords: magnetic fields - plasmas - ISM: bubbles - ISM: general -
ISM: magnetic fields - ISM: structure
Abstract:
Magnetic fields permeate the diffuse interstellar medium (ISM) of the
Milky Way, and are essential to explain the dynamical evolution and
current shape of the Galaxy. Magnetic fields reveal themselves via
their influence on the surrounding matter, and as such are notoriously
hard to measure independently of other tracers.
In this work, we attempt to disentangle an all sky map of the
line-of-sight parallel component of the Galactic magnetic field from
the Faraday effect, utilizing several tracers of the Galactic electron
density. Additionally, we aim to produce a Galactic electron
dispersion measure map and quantify several tracers of the structure
of the ionized medium of the Milky Way.
The method developed to reach these aims is based on information field
theory, a Bayesian inference framework for fields, which performs well
when handling noisy and incomplete data and constraining high
dimensional parameter spaces. We rely on compiled catalogs of
extragalactic Faraday rotation measures and Galactic pulsar dispersion
measures, a well as data on bremsstrahlung and the hydrogen α
spectral line to trace the ionized medium of the Milky Way.
We present the first full sky map of the line-of-sight averaged
Galactic magnetic field. Within this map, we find LoS parallel and
LoS-averaged magnetic field strengths of up to 4uG, with an all-sky
root-mean-square of 1.1uG, which is consistent with previous local
measurements and global magnetic field models. Additionally, we
produce a detailed electron dispersion measure map, which agrees with
already existing parametric models at high latitudes, but suffers from
systematic effects in the disk. Further analysis of our results with
regard to the 3D structure of ne reveals that it follows a
Kolmogorov-type turbulence for most of the sky. From the reconstructed
dispersion measure and emission measure maps we construct several
tracers of variability of ne along the LoS.
This work demonstrates the power of consistent joint statistical
analysis including multiple data sets and physical quantities and
defines a roadmap towards a full three-dimensional joint
reconstruction of the Galactic magnetic field and the ionized ISM.
Description:
This data set contains the statistical results for 5 different sky
models, namely:
- The integrated LoS component of the Galactic magnetic field,
weighted by electron density
- The LoS-integrated electron density of the Milky Way, i.e. the
Galactic dispersion measure
- The integrated squared electron density of the Milky Way, i.e. the
Galactic emission measure
- Conversion factor between squared DM and EM, can be interpreted as
the length of the LoS in ideal conditions
- Conversion factor between EM and DM, can be interpreted as the
LoS-averaged electron density of the Milky Way in ideal conditions
The results for these models are provided by reporting sky maps of the
posterior mean and the corresponding standard deviation. Note that the
uncertainties of individual pixels and the different sky maps are
correlated, for a detailed analysis using the posterior samples is
recommended.
These are provided for the integrated LoS component of the Galactic
magnetic field, the logarithmic DM and the logarithmic L_DM2EM. From
those, the uncertainties of all other sky maps can be estimated using
the equations in the paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 178 5 List of fits maps
fits/* . 5 Individual fits maps
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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- 2 I2 --- Nx Number of pixels along X-axis
4- 9 I6 --- Ny Number of pixels along Y-axis
11- 15 I5 Kibyte size Size of FITS file
17- 38 A22 --- FileName Name of FITS file, in subdirectory fits
40-178 A139 --- Title Title of the FITS file
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Acknowledgements:
Sebastian Hutschenreuter, sebastian.hutschenreuter(at)univie.ac.at
References:
Van Eck et al., 2023ApJS..267...28V 2023ApJS..267...28V,
RMTable2023 and PolSpectra2023: Standards for Reporting
Polarization and Faraday Rotation Measurements of Radio Sources
(End) S. Hutschenreuter [Vienna Univ., Austria], P. Vannier [CDS] 07-Aug-2024