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

Jaffe, T. R.

doi:10.3390/galaxies7020052

Cited by 48 publications

(39 citation statements)

References 99 publications

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“…The global structure of the Galactic magnetic field (GMF) is an outstanding problem in astrophysics, with wide-ranging consequences for understanding cosmic ray propagation, dynamo theory, star formation, and galactic evolution (Haverkorn 2015;Jaffe 2019). At present, the state-of-the-art data-driven models for the Galactic magnetic field are parametric fits to a few observables, typically some subset of extragalactic and pulsar rotation measures (RMs), synchrotron emission, and polar-ized dust emission (e.g.…”

Section: Relevance For Global Magnetic Field Modelingmentioning

confidence: 99%

Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen

Clark¹,

Hensley²

2019

ApJ

149

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Recent analyses of 21-cm neutral hydrogen (H i) emission have demonstrated that H i gas is organized into linear filamentary structures that are preferentially aligned with the local magnetic field, and that the coherence of these structures in velocity space traces line-of-sight magnetic field tangling. On this basis, we introduce a paradigm for modeling the properties of magnetized, dusty regions of the interstellar medium, using the orientation of H i structure at different velocities to map "magnetically coherent" regions of space. We construct three-dimensional (position-position-velocity) Stokes parameter maps using H i4PI full-sky spectroscopic H i data. We compare these maps, integrated over the velocity dimension, to Planck maps of the polarized dust emission at 353 GHz. Without any free parameters governing the relation between H i intensity and dust emission, we find that our Q and U maps are highly correlated (r > 0.75) with the 353 GHz Q and U maps of polarized dust emission observed by Planck and reproduce many of its large-scale features. The E/B ratio of the dust emission maps agrees well with the H i-derived maps at large angular scales ( 120), supporting the interpretation that this asymmetry arises from the coupling of linear density structures to the Galactic magnetic field. We demonstrate that our 3D Stokes parameter maps constrain the 3D structure of the Galactic interstellar medium and the orientation of the interstellar magnetic field.

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Section: Relevance For Global Magnetic Field Modelingmentioning

confidence: 99%

Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen

Clark¹,

Hensley²

2019

ApJ

149

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“…1 Other definitions of "ordered field" are used in the literature, e.g. in [47]. It is tempting to equate the regular field B reg with the mean field B of dynamo theory, and the combined vector B an + B iso with the fluctuating field b.…”

Section: Observationsmentioning

confidence: 99%

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

et al. 2019

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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. Further, 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.

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“…XX 2015;Planck Collaboration XII 2018). bhensley@astro.princeton.edu Because of the importance of the Galactic magnetic field in many areas of astrophysics, including cosmic ray propagation, the formation and structure of the Milky Way, and polarized foregrounds for Cosmic Microwave Background (CMB) science, constraining its morphology has been the subject of much research (see Jaffe 2019, for a recent review). With the sensitive, full-sky Planck maps, dust emission is actively being used to complement other tracers, such as synchrotron emission and pulsar rotation measures, yielding insights on both the large-scale field morphology and the Local Bubble (e.g., Planck Collaboration Int.…”

Section: Introductionmentioning

confidence: 99%

An Imprint of the Galactic Magnetic Field in the Diffuse Unpolarized Dust Emission

Hensley

Zhang

Bock

2019

ApJ

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It is well known that aligned, aspherical dust grains emit polarized radiation and that the degree of polarization depends on the angle ψ between the interstellar magnetic field and the line of sight. However, anisotropy of the dust absorption cross sections also modulates the total intensity of the radiation as the viewing geometry changes. We report a detection of this effect in the high Galactic latitude Planck data, finding that the 353 GHz dust intensity per N H i is smaller when the Galactic magnetic field is mostly in the plane of the sky and larger when the field is mostly along the line of sight. These variations are of opposite sign and roughly equal magnitude as the changes in polarized intensity per N H i with ψ, as predicted. In principle, the variation in intensity can be used in conjunction with the dust polarization angle to constrain the full 3D orientation of the Galactic magnetic field.

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

Cited by 48 publications

References 99 publications

Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen

Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen

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

An Imprint of the Galactic Magnetic Field in the Diffuse Unpolarized Dust Emission

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