scholarly journals GALACTIC MAGNETIC FIELDS AND THE LARGE-SCALE ANISOTROPY AT MILAGRO

2009 ◽  
Vol 703 (1) ◽  
pp. L90-L93 ◽  
Author(s):  
Eduardo Battaner ◽  
Joaquín Castellano ◽  
Manuel Masip
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Galactic Magnetic Fields

scholarly journals Galactic Dynamos Without Sharp Boundaries: Non-Axisymmetric Fields in Axisymmetric Disks?

1990 ◽  
Vol 140 ◽  
pp. 115-116
Author(s):  
R. Meinel ◽  
D. Elstner ◽  
G. Rüdiger ◽  
F. Krause
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Galactic Magnetic Fields ◽  
Axisymmetric Structure ◽  
Galactic Dynamos

Radio polarization observations of spiral galaxies suggest the existence of large-scale galactic magnetic fields which are of either axisymmetric -spiral (ASS) or bisymmetric-spiral (BSS), i.e. non-axisymmetric, structure (cf. Beck, 1939). Clear evidence for a BSS field was indicated for M31 by M. Krause et al. (1989).

scholarly journals Observations of Galactic Magnetic Fields

2002 ◽  
Vol 12 ◽  
pp. 712-715 ◽  
Author(s):  
Rainer Beck
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Density Wave ◽  
Upstream Region ◽  
Galactic Magnetic Fields ◽  
Barred Galaxies ◽  
Angular Momentum Transport ◽  
Central Regions ◽  
Spiral Structures ◽  
Field Lines

AbstractMagnetic fields are anchored in gas clouds. Field lines are tangled in spiral arms, but highly regularbetweenthe arms. The similarity of pitch angles between gaseous and magnetic arms suggests a coupling between the density wave and the magnetic wave. Observations of large-scale patterns in Faraday rotation favour a dynamo origin of the regular fields. Fields in barred galaxies do not reveal the strong shearing shocks observed in the cold gas, but swing smoothly from the upstream region into the bar. Magnetic fields are important for the dynamics of gas clouds, for the formation of spiral structures, bars and halos, and for mass and angular momentum transport in central regions.

scholarly journals Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

Galaxies ◽  
2019 ◽  
Vol 8 (1) ◽  
pp. 4 ◽  
Author(s):  
Rainer Beck ◽  
Luke Chamandy ◽  
Ed Elson ◽  
Eric G. Blackman
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Mean Field ◽  
Large Data ◽  
Data Sets ◽  
Dynamo Theory ◽  
Galactic Magnetic Fields ◽  
Ngc 6946 ◽  
Upper Limits ◽  
New Instruments

Constraining dynamo theories of magnetic field origin by observation is indispensable but challenging, in part because the basic quantities measured by observers and predicted by modelers are different. We clarify these differences and sketch out ways to bridge the divide. Based on archival and previously unpublished data, we then compile various important properties of galactic magnetic fields for nearby spiral galaxies. We consistently compute strengths of total, ordered, and regular fields, pitch angles of ordered and regular fields, and we summarize the present knowledge on azimuthal modes, field parities, and the properties of non-axisymmetric spiral features called magnetic arms. We review related aspects of dynamo theory, with a focus on mean-field models and their predictions for large-scale magnetic fields in galactic discs and halos. Furthermore, we measure the velocity dispersion of H i gas in arm and inter-arm regions in three galaxies, M 51, M 74, and NGC 6946, since spiral modulation of the root-mean-square turbulent speed has been proposed as a driver of non-axisymmetry in large-scale dynamos. We find no evidence for such a modulation and place upper limits on its strength, helping to narrow down the list of mechanisms to explain magnetic arms. Successes and remaining challenges of dynamo models with respect to explaining observations are briefly summarized, and possible strategies are suggested. With new instruments like the Square Kilometre Array (SKA), large data sets of magnetic and non-magnetic properties from thousands of galaxies will become available, to be compared with theory.

scholarly journals Practical Modeling of Large-Scale Galactic Magnetic Fields: Status and Prospects

Galaxies ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 52 ◽  
Author(s):  
Tess R. Jaffe
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Galactic Magnetic Field ◽  
Galactic Magnetic Fields ◽  
The Status

This is a review of the status of efforts to model the large-scale Galactic magnetic field (GMF). Though important for a variety of astrophysical processes, the GMF remains poorly understood despite some interesting new tracers being used in the field. Though we still have too many models that might fit the data, this is not to say that the field has not developed in the last few years. In particular, surveys of polarized dust have given us a new observable that is complementary to the more traditional radio tracers, and a variety of other new tracers and related measurements are becoming available to improve current modeling. This paper reviews: the tracers available; the models that have been studied; what has been learned so far; what the caveats and outstanding issues are; and one opinion of where the most promising future avenues of exploration lie.

scholarly journals PRIMORDIAL MAGNETIC FIELDS

1998 ◽  
Vol 07 (03) ◽  
pp. 331-349 ◽  
Author(s):  
KARI ENQVIST
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Particle Physics ◽  
Large Scale ◽  
Magnetic Energy ◽  
Galactic Magnetic Fields ◽  
Microscopic Field ◽  
Primordial Magnetic Fields ◽  
Primordial Magnetic Field ◽  
The Magnetic Field

The explanation of the observed galactic magnetic fields may require the existence of a primordial magnetic field. Such a field may arise during the early cosmological phase transitions, or because of other particle physics related phenomena in the very early universe reviewed here. The turbulent evolution of the initial, randomly fluctuating microscopic field to a large-scale macroscopic field can be described in terms of a shell model, which provides an approximation to the complete magnetohydrodynamics. The results indicate that there is an inverse cascade of magnetic energy whereby the coherence of the magnetic field is increased by many orders of magnitude. Cosmological seed fields roughly of the order of 10-20 G at the scale of protogalaxy, as required by the dynamo explanation of galactic magnetic fields, thus seem plausible.

scholarly journals Multiwavelength Magnetic Field Modeling

2012 ◽  
Vol 10 (H16) ◽  
pp. 401-401
Author(s):  
T. R. Jaffe
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Dust Emission ◽  
Subsequent Work ◽  
Galactic Magnetic Fields ◽  
Preliminary Results ◽  
Field Modeling ◽  
Magnetic Field Modeling ◽  
Spiral Arm

AbstractWe model the large-scale Galactic magnetic fields, including a spiral arm compression to generate anisotropic turbulence, by comparing polarized synchrotron and thermal dust emission. Preliminary results show that in the outer Galaxy, the dust emission comes from regions where the fields are more ordered than average while the situation is reversed in the inner Galaxy. We will attempt in subsequent work to present a more complete picture of what the comparison of these observables tells us about the distribution of the components of the magnetized ISM and about the physics of spiral arm shocks and turbulence.

Global Magnetic Structure In Spiral Galaxies

1991 ◽  
Vol 9 (1) ◽  
pp. 95-97
Author(s):  
S. J. Spencer
Keyword(s):  
Magnetic Fields ◽  
Magnetic Structure ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Three Dimensional ◽  
Optical Observations ◽  
Dynamo Model ◽  
Galactic Magnetic Fields ◽  
Large Scale Magnetic Field ◽  
Analytical Expressions

AbstractGlobal magnetic structure has been inferred in spiral galaxies from radio and optical observations. The author has developed a three dimensional, quasi-global kinematic dynamo model which demonstrates the possibility of maintaining large-scale magnetic fields by the αω mechanism. Analytical expressions for large-scale galactic magnetic fields near temporal steady states have been derived. Illustrations of the spatial distribution of vector and absolute large-scale magnetic field strength are presented. When coupled with observations this model may help in understanding the maintenance and morphologies inferred for disk and halo global magnetic fields in spiral galaxies.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

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