Can the large-scale magnetic field lines cross the spiral arms in our Milky Way galaxy?

1988 ◽  
Vol 95 ◽  
pp. 750 ◽  
Author(s):  
J. P. Vallee
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Milky Way ◽  
Milky Way Galaxy ◽  
Spiral Arms ◽  
Large Scale Magnetic Field ◽  
Field Lines

scholarly journals A bisymmetric spiral magnetic field in the Milky Way

1985 ◽  
Vol 106 ◽  
pp. 251-252
Author(s):  
Y. Sofue ◽  
M. Fujimoto
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Large Scale ◽  
Milky Way ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
The Galaxy ◽  
Field Lines

The distribution of Faraday rotation measure (RM) of extragalactic radio sources shows that a large-scale magnetic field in the Galaxy is oriented along the spiral arms. The field lines change direction from one arm to the next in the inter-arm region.

scholarly journals Probing Magnetic Fields With SNRs

2012 ◽  
Vol 10 (H16) ◽  
pp. 395-395
Author(s):  
Roland Kothes
Keyword(s):  
Magnetic Field ◽  
Simple Model ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Large Scale ◽  
Milky Way ◽  
Magnetic Energy ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
Field Lines

AbstractAs supernova remnants (SNRs) expand, their shock waves freeze in and compress magnetic field lines they encounter; consequently we can use SNRs as magnifying glasses for interstellar magnetic fields. A simple model is used to derive polarization and rotation measure (RM) signatures of SNRs. This model is exploited to gain knowledge about the large-scale magnetic field in the Milky Way. Three examples are given which indicate a magnetic anomaly, an azimuthal large-scale magnetic field towards the anti-centre, and a chimney that releases magnetic energy from the plane into the halo.

scholarly journals Probing interstellar magnetic fields with Supernova remnants

2008 ◽  
Vol 4 (S259) ◽  
pp. 75-80 ◽  
Author(s):  
Roland Kothes ◽  
Jo-Anne Brown
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Large Scale ◽  
Galactic Plane ◽  
Field Configuration ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
Field Lines ◽  
The Magnetic Field

AbstractAs Supernova remnants expand, their shock waves are freezing in and compressing the magnetic field lines they encounter; consequently we can use Supernova remnants as magnifying glasses for their ambient magnetic fields. We will describe a simple model to determine emission, polarization, and rotation measure characteristics of adiabatically expanding Supernova remnants and how we can exploit this model to gain information about the large scale magnetic field in our Galaxy. We will give two examples: The SNR DA530, which is located high above the Galactic plane, reveals information about the magnetic field in the halo of our Galaxy. The SNR G182.4+4.3 is located close to the anti-centre of our Galaxy and reveals the most probable direction where the large-scale magnetic field is perpendicular to the line of sight. This may help to decide on the large-scale magnetic field configuration of our Galaxy. But more observations of SNRs are needed.

scholarly journals Rotation Measures of Extragalactic Sources behind the Southern Galactic Plane: New Insights into the Large‐Scale Magnetic Field of the Inner Milky Way

2007 ◽  
Vol 663 (1) ◽  
pp. 258-266 ◽  
Author(s):  
J. C. Brown ◽  
M. Haverkorn ◽  
B. M. Gaensler ◽  
A. R. Taylor ◽  
N. S. Bizunok ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Plane ◽  
Large Scale Magnetic Field

scholarly journals Magnetic Flux Transport in Protostellar Accretion Disks

1997 ◽  
Vol 163 ◽  
pp. 692-692
Author(s):  
John Contopoulos ◽  
Arieh Königl
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Accretion Disks ◽  
Large Scale ◽  
Turbulent Viscosity ◽  
Flux Transport ◽  
Disk Structure ◽  
Large Scale Magnetic Field ◽  
Field Lines ◽  
Open Magnetic Field

AbstractCentrifugally driven winds from the surfaces of magnetized accretion disks are a leading candidate for the origin of bipolar outflows and have also been recognized as an attractive mechanism for removing the angular momentum of the accreted matter. The origin of the open magnetic field lines that thread the disk in this scenario is, however, still uncertain. One possibility is that the field lines are transported through the disk, but previous studies have shown that this process is inefficient in disks with turbulent viscosity and diffusivity. Here we examine whether the efficiency can be increased if angular momentum is transported from the disk surfaces by large-scale magnetic fields instead of radially by viscous stresses. In this picture, the removal of angular momentum is associated with the establishment of a global poloidal electric current driven by the radial EMF in the disc, and it does not necessarily need to involve super-Alfvénic outflows. We address this problem in the context of protostellar systems and present representative solutions of the time evolution of a resistive disk that is initially threaded by a uniform vertical field anchored at a large distance from its surfaces. We assume that the angular momentum transport in the disk is controlled by the large-scale magnetic field and take into account the influence of the field on the disk structure.

scholarly journals A physical approach to modelling large-scale galactic magnetic fields

2019 ◽  
Vol 623 ◽  
pp. A113 ◽  
Author(s):  
Anvar Shukurov ◽  
Luiz Felippe S. Rodrigues ◽  
Paul J. Bushby ◽  
James Hollins ◽  
Jörg P. Rachen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Milky Way ◽  
Mean Field ◽  
Axially Symmetric ◽  
Dynamo Action ◽  
Disc Galaxy ◽  
Large Scale Magnetic Field ◽  
Dynamo Equation

Context. A convenient representation of the structure of the large-scale galactic magnetic field is required for the interpretation of polarization data in the sub-mm and radio ranges, in both the Milky Way and external galaxies. Aims. We develop a simple and flexible approach to construct parametrised models of the large-scale magnetic field of the Milky Way and other disc galaxies, based on physically justifiable models of magnetic field structure. The resulting models are designed to be optimised against available observational data. Methods. Representations for the large-scale magnetic fields in the flared disc and spherical halo of a disc galaxy were obtained in the form of series expansions whose coefficients can be calculated from observable or theoretically known galactic properties. The functional basis for the expansions is derived as eigenfunctions of the mean-field dynamo equation or of the vectorial magnetic diffusion equation. Results. The solutions presented are axially symmetric but the approach can be extended straightforwardly to non-axisymmetric cases. The magnetic fields are solenoidal by construction, can be helical, and are parametrised in terms of observable properties of the host object, such as the rotation curve and the shape of the gaseous disc. The magnetic field in the disc can have a prescribed number of field reversals at any specified radii. Both the disc and halo magnetic fields can separately have either dipolar or quadrupolar symmetry. The model is implemented as a publicly available software package GALMAG which allows, in particular, the computation of the synchrotron emission and Faraday rotation produced by the model’s magnetic field. Conclusions. The model can be used in interpretations of observations of magnetic fields in the Milky Way and other spiral galaxies, in particular as a prior in Bayesian analyses. It can also be used for a simple simulation of a time-dependent magnetic field generated by dynamo action.

scholarly journals The complex large-scale magnetic fields in the first Galactic quadrant as revealed by the Faraday depth profile disparity

2020 ◽  
Vol 497 (3) ◽  
pp. 3097-3117
Author(s):  
Y K Ma ◽  
S A Mao ◽  
A Ordog ◽  
J C Brown
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Milky Way ◽  
Broad Band ◽  
Galactic Magnetic Field ◽  
Field Reversal ◽  
Very Large Array ◽  
Large Scale Magnetic Field ◽  
Galactic Longitude ◽  
Spiral Arm

ABSTRACT The Milky Way is one of the very few spiral galaxies known to host large-scale magnetic field reversals. The existence of the field reversal in the first Galactic quadrant near the Sagittarius spiral arm has been well established, yet poorly characterized due to the insufficient number of reliable Faraday depths (FDs) from extragalactic radio sources (EGSs) through this reversal region. We have therefore performed broad-band (1–$2\, {\rm GHz}$) spectropolarimetric observations with the Karl G. Jansky Very Large Array (VLA) to determine the FD values of 194 EGSs in the Galactic longitude range of 20°–52° within ±5° from the Galactic mid-plane, covering the Sagittarius arm tangent. This factor of five increase in the EGS FD density has led to the discovery of a disparity in FD values across the Galactic mid-plane in the Galactic longitude range of 40°–52°. Combined with existing pulsar FD measurements, we suggest that the Sagittarius arm can host an odd-parity disc field. We further compared our newly derived EGS FDs with the predictions of three major Galactic magnetic field models, and concluded that none of them can adequately reproduce our observational results. This has led to our development of new, improved models of the Milky Way disc magnetic field that will serve as an important step towards major future improvements in Galactic magnetic field models.

scholarly journals Helicity in the large-scale Galactic magnetic field

2020 ◽  
Vol 499 (3) ◽  
pp. 3673-3689
Author(s):  
J L West ◽  
R N Henriksen ◽  
K Ferrière ◽  
A Woodfinden ◽  
T Jaffe ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Milky Way ◽  
Vertical Component ◽  
Synchrotron Emission ◽  
Complex Field ◽  
Galactic Magnetic Field ◽  
Milky Way Galaxy ◽  
Dynamo Equation ◽  
Helical Field

ABSTRACT We search for observational signatures of magnetic helicity in data from all-sky radio polarization surveys of the Milky Way Galaxy. Such a detection would help confirm the dynamo origin of the field and may provide new observational constraints for its shape. We compare our observational results to simulated observations for both a simple helical field, and for a more complex field that comes from a solution to the dynamo equation. Our simulated observations show that the large-scale helicity of a magnetic field is reflected in the large-scale structure of the fractional polarization derived from the observed synchrotron radiation and Faraday depth of the diffuse Galactic synchrotron emission. Comparing the models with the observations provides evidence for the presence of a quadrupolar magnetic field with a vertical component that is pointing away from the observer in both hemispheres of the Milky Way Galaxy. Since there is no reason to believe that the Galactic magnetic field is unusual when compared to other galaxies, this result provides further support for the dynamo origin of large-scale magnetic fields in galaxies.

scholarly journals On Galactic magnetic field derived from RMs of pulsars

1996 ◽  
Vol 160 ◽  
pp. 485-486 ◽  
Author(s):  
J.L. Han ◽  
G.J. Qiao
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Galactic Latitude ◽  
High Galactic Latitude ◽  
Spiral Arms ◽  
Large Scale Magnetic Field ◽  
Large Scale Field ◽  
Magnetic Rings

AbstractRMs of all 262 pulsars are used to see the large scale magnetic field of our Galaxy. We find that: (1). RMs of 91 pulsars at high galactic latitude (|b| > 8.6°) show two toroidal magnetic rings antisymmetric with respect to galactic plane. These data shouldn’t be used for modelling the large scale field in Galactic disk; (2). pulsars at low galactic latitude are concentrated on the spiral arms; (3). the directions of fields have a similar pitch angle to that of spiral arms.

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