Structure in the radiation of the galactic disk

1967 ◽  
Vol 31 ◽  
pp. 355-356
Author(s):  
R. D. Davies
Keyword(s):  
Magnetic Field ◽  
Galactic Disk ◽  
Galactic Magnetic Field ◽  
Measured Polarization

Observations at various frequencies between 136 and 1400 MHz indicate a considerable amount of structure in the galactic disk. This result appears consistent both with measured polarization percentages and with considerations of the strength of the galactic magnetic field.

scholarly journals Faraday Rotation of Extended Emission as a Probe of the Large-Scale Galactic Magnetic Field

Galaxies ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 43 ◽  
Author(s):  
Anna Ordog ◽  
Rebecca Booth ◽  
Cameron Van Eck ◽  
Jo-Anne Brown ◽  
Thomas Landecker
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Large Scale ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Galactic Magnetic Field ◽  
Galactocentric Distance ◽  
Linear Fit ◽  
Unused Resource ◽  
Extended Emission

The Galactic magnetic field is an integral constituent of the interstellar medium (ISM), and knowledge of its structure is crucial to understanding Galactic dynamics. The Rotation Measures (RM) of extragalactic (EG) sources have been the basis of comprehensive Galactic magnetic field models. Polarised extended emission (XE) is also seen along lines of sight through the Galactic disk, and also displays the effects of Faraday rotation. Our aim is to investigate and understand the relationship between EG and XE RMs near the Galactic plane, and to determine how the XE RMs, a hitherto unused resource, can be used as a probe of the large-scale Galactic magnetic field. We used polarisation data from the Canadian Galactic Plane Survey (CGPS), observed near 1420 MHz with the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope. We calculated RMs from a linear fit to the polarisation angles as a function of wavelength squared in four frequency channels, for both the EG sources and the XE. Across the CGPS area, 55 ∘ < ℓ < 193 ∘ , − 3 ∘ < b < 5 ∘ , the RMs of the XE closely track the RMs of the EG sources, with XE RMs about half the value of EG-source RMs. The exceptions are places where large local HII complexes heavily depolarise more distant emission. We conclude that there is valuable information in the XE RM dataset. The factor of 2 between the two types of RM values is close to that expected from a Burn slab model of the ISM. This result indicates that, at least in the outer Galaxy, the EG and XE sources are likely probing similar depths, and that the Faraday rotating medium and the synchrotron emitting medium have similar variation with galactocentric distance.

scholarly journals The galactic magnetic field derived from cosmic-ray electrons

1968 ◽  
Vol 46 (10) ◽  
pp. S642-S645 ◽  
Author(s):  
H. Okuda ◽  
Y. Tanaka
Keyword(s):  
Magnetic Field ◽  
Solar System ◽  
Electron Spectrum ◽  
Galactic Center ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Field Configuration ◽  
Galactic Magnetic Field ◽  
Upper Limits ◽  
The Magnetic Field

An estimate of the galactic magnetic field is obtained by combining new results in the cosmic-ray electron spectrum and the recent radio data. The lower and upper limits of the magnetic field in the galactic disk are derived from two alternative models of field configuration; i.e. (0.5–1.0) × 10−5 gauss near the solar system and (1.0–2.0) × 10−5 gauss near the galactic center, respectively. The magnetic field in the halo is estimated to be larger than 2.5 × 10−6 gauss.

Observing the galactic magnetic field

1967 ◽  
Vol 31 ◽  
pp. 375-380
Author(s):  
H. C. van de Hulst
Keyword(s):  
Magnetic Field ◽  
Fair Agreement ◽  
Solar Neighbourhood ◽  
Galactic Magnetic Field ◽  
The Magnetic Field

Various methods of observing the galactic magnetic field are reviewed, and their results summarized. There is fair agreement about the direction of the magnetic field in the solar neighbourhood:l= 50° to 80°; the strength of the field in the disk is of the order of 10-5gauss.

The galactic magnetic field

1977 ◽  
Vol 121 (4) ◽  
pp. 679 ◽  
Author(s):  
T.A.T. Spoelstra
Keyword(s):  
Magnetic Field ◽  
Galactic Magnetic Field

scholarly journals Interstellar Matters: Neutral Hydrogen and the Galactic Magnetic Field

2018 ◽  
Vol 867 (2) ◽  
pp. 139 ◽  
Author(s):  
G. L. Verschuur ◽  
J. T. Schmelz ◽  
M. Asgari-Targhi
Keyword(s):  
Magnetic Field ◽  
Neutral Hydrogen ◽  
Galactic Magnetic Field

scholarly journals LIGHT SUPERCONDUCTING STRINGS IN THE GALAXY

2007 ◽  
Vol 16 (12b) ◽  
pp. 2399-2405 ◽  
Author(s):  
FRANCESC FERRER ◽  
TANMAY VACHASPATI
Keyword(s):  
Magnetic Field ◽  
Spatial Distribution ◽  
Particle Physics ◽  
Milky Way ◽  
Gamma Ray ◽  
Galactic Center ◽  
Line Emission ◽  
Galactic Magnetic Field ◽  
The Galaxy ◽  
Intense Source

Observations of the Milky Way by the SPI/INTEGRAL satellite have confirmed the presence of a strong 511 keV gamma ray line emission from the bulge, which requires an intense source of positrons in the galactic center. These observations are hard to account for by conventional astrophysical scenarios, whereas other proposals, such as light DM, face stringent constraints from the diffuse gamma ray background. Here we suggest that light superconducting strings could be the source of the observed 511 keV emission. The associated particle physics, at the ~ 1 TeV scale, is within the reach of planned accelerator experiments, while the distinguishing spatial distribution, proportional to the galactic magnetic field, could be mapped by SPI or by future, more sensitive satellite missions.

scholarly journals Is there a left-handed magnetic field in the solar neighborhood?

2019 ◽  
Vol 621 ◽  
pp. A97 ◽  
Author(s):  
A. Bracco ◽  
S. Candelaresi ◽  
F. Del Sordo ◽  
A. Brandenburg
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Power Spectra ◽  
Field Structure ◽  
Solar Neighborhood ◽  
Galactic Magnetic Field ◽  
Polarization Data ◽  
Left Handed ◽  
Cross Correlations

Context. The analysis of the full-sky Planck polarization data at 850 μm revealed unexpected properties of the E- and B-mode power spectra of dust emission in the interstellar medium (ISM). The positive cross-correlations over a wide range of angular scales between the total dust intensity, T, and both E and (most of all) B modes has raised new questions about the physical mechanisms that affect dust polarization, such as the Galactic magnetic field structure. This is key both to better understanding ISM dynamics and to accurately describing Galactic foregrounds to the polarization of the cosmic microwave background (CMB). In particular, in the quest to find primordial B modes of the CMB, the observed positive cross-correlation between T and B for interstellar dust requires further investigation towards parity-violating processes in the ISM. Aims. In this theoretical paper we investigate the possibility that the observed cross-correlations in the dust polarization power spectra, and specifically the one between T and B, can be related to a parity-odd quantity in the ISM such as the magnetic helicity. Methods. We produce synthetic dust polarization data, derived from 3D analytical toy models of density structures and helical magnetic fields, to compare with the E and B modes of observations. We present several models. The first is an ideal fully helical isotropic case, such as the Arnold-Beltrami-Childress field. Second, following the nowadays favored interpretation of the T–E signal in terms of the observed alignment between the magnetic field morphology and the filamentary density structure of the diffuse ISM, we design models for helical magnetic fields wrapped around cylindrical interstellar filaments. Lastly, focusing on the observed T–B correlation, we propose a new line of interpretation of the Planck observations advocating the presence of a large-scale helical component of the Galactic magnetic field in the solar neighborhood. Results. Our analysis shows that: I) the sign of magnetic helicity does not affect E and B modes for isotropic magnetic-field configurations; II) helical magnetic fields threading interstellar filaments cannot reproduce the Planck results; and III) a weak helical left-handed magnetic field structure in the solar neighborhood may explain the T–B correlation seen in the Planck data. Such a magnetic-field configuration would also account for the observed large-scale T–E correlation. Conclusions. This work suggests a new perspective for the interpretation of the dust polarization power spectra that supports the imprint of a large-scale structure of the Galactic magnetic field in the solar neighborhood.

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