English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Constraining dynamo theories of magnetic field origin by observation isindispensable but challenging, in part because the basic quantities measured byobservers and predicted by modelers are different. We clarify these differencesand sketch out ways to bridge the divide. Based on archival and previouslyunpublished data, we then compile various important properties of galacticmagnetic fields for nearby spiral galaxies. We consistently compute strengthsof total, ordered, and regular fields, pitch angles of ordered and regularfields, and we summarize the present knowledge on azimuthal modes, fieldparities, and the properties of non-axisymmetric spiral features calledmagnetic arms. We review related aspects of dynamo theory, with a focus onmean-field models and their predictions for large-scale magnetic fields ingalactic discs and halos. Further, we measure the velocity dispersion of HI gasin arm and inter-arm regions in three galaxies, M 51, M 74, and NGC 6496, sincespiral modulation of the root-mean-square turbulent speed has been proposed asa driver of non-axisymmetry in large-scale dynamos. We find no evidence forsuch a modulation and place upper limits on its strength, helping to narrowdown the list of mechanisms to explain magnetic arms. Successes and remainingchallenges of dynamo models with respect to explaining observations are brieflysummarized, and possible strategies are suggested. With new instruments likethe Square Kilometre Array (SKA), large data sets of magnetic and non-magneticproperties from thousands of galaxies will become available, to be comparedwith theory.

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