The distribution of mean and fluctuating magnetic fields in the multiphase interstellar medium

Evirgen, C. C.; Gent, Frederick A.; Shukurov, Anvar; Fletcher, Andrew; Bushby, P. J.

doi:10.1093/mnrasl/slw196

Cited by 31 publications

(41 citation statements)

References 20 publications

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“…A magnetic field of a few µG in strength can hardly affect expanding supernova remnants, so it is likely that it reduces the abundance of the hot, rarefied gas in old remnants or facilitates their merger with the ambient gas. Evirgen et al (2017a) arrive at similar conclusions from their analysis of the fractional volume of the hot gas. Remarkably, the modification of the gas distribution by magnetic field is captured reliably even in a region at |z| > ∼ 300 pc where the magnetic field is weaker and correlation analysis fails to detect any magnetic effects.…”

Section: Discussionsupporting

confidence: 63%

“…As discussed by Evirgen et al (2017a), the magnetic field is strongest at |z| = 200-300 pc, so its effects on the gas distribution can be expected to be most pronounced there. However, the autocorrelation functions do not show any signs of this.…”

Section: Autocorrelation Function Of Gas Densitymentioning

confidence: 95%

“…The reduction is stronger for the number of holes, B 1 . At large values of |z|, where the magnetic field is weaker (Evirgen et al 2017b), the change in B n between Stages I and III is weaker too. The only exception is the case of B 0 at z = 0.5 kpc where the change is marginal.…”

Section: Betti Numbers Of the Gas Density Fluctuationsmentioning

confidence: 97%

“…The magnetic field is arguably the least well understood component of the ISM, both observationally and theoretically, but its importance is becoming more evident. However, progress is slow because the effects of a magnetic field can be subtle and not easy to discern (see Evirgen et al 2017a, and references therein). We focus upon the ways in which the gas density distribution in the simulated ISM is influenced by the presence of magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

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Topological signatures of interstellar magnetic fields – I. Betti numbers and persistence diagrams

Makarenko

Shukurov

Henderson

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The interstellar medium (ISM) is a magnetised system in which transonic or supersonic turbulence is driven by supernova explosions. This leads to the production of intermittent, filamentary structures in the ISM gas density, whilst the associated dynamo action also produces intermittent magnetic fields. The traditional theory of random functions, restricted to second-order statistical moments (or power spectra), does not adequately describe such systems. We apply topological data analysis (TDA), sensitive to all statistical moments and independent of the assumption of Gaussian statistics, to the gas density fluctuations in a magnetohydrodynamic (MHD) simulation of the multi-phase ISM. This simulation admits dynamo action, so produces physically realistic magnetic fields. The topology of the gas distribution, with and without magnetic fields, is quantified in terms of Betti numbers and persistence diagrams. Like the more standard correlation analysis, TDA shows that the ISM gas density is sensitive to the presence of magnetic fields. However, TDA gives us important additional information that cannot be obtained from correlation functions. In particular, the Betti numbers per correlation cell are shown to be physically informative. Magnetic fields make the ISM more homogeneous, reducing the abundance of both isolated gas clouds and cavities, with a stronger effect on the cavities. Remarkably, the modification of the gas distribution by magnetic fields is captured by the Betti numbers even in regions more than 300 pc from the midplane, where the magnetic field is weaker and correlation analysis fails to detect any signatures of magnetic effects.

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Section: Discussionsupporting

confidence: 63%

Section: Autocorrelation Function Of Gas Densitymentioning

confidence: 95%

Section: Betti Numbers Of the Gas Density Fluctuationsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Topological signatures of interstellar magnetic fields – I. Betti numbers and persistence diagrams

Makarenko

Shukurov

Henderson

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…The importance of separating these components is in measuring their relative amplitudes and understanding the relationships among them, e.g., how much of the regular field may arise from large-scale differential rotation and shear, or shocks that compress the turbulent component along one direction, etc. The next step is then to associate them with the distinct regions or phases of the ISM (see, e.g., Evirgen et al [44]) to understand their relationship with the other components of the Galaxy.…”

mentioning

confidence: 99%

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

Jaffe

2019

Galaxies

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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.

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Modelling and simulation of large-scale polarized dust emission over the southern Galactic cap using the GASS Hi data

Ghosh

Boulanger

Martín

et al. 2017

A&A

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The Planck survey has quantified polarized Galactic foregrounds and established that they are a main limiting factor in the quest for the cosmic microwave background B-mode signal induced by primordial gravitational waves during cosmic inflation. Accurate separation of the Galactic foregrounds therefore binds this quest to our understanding of the magnetized interstellar medium. The two most relevant empirical results from analysis of Planck data are line of sight depolarization arising from fluctuations of the Galactic magnetic field orientation and alignment of filamentary dust structures with the magnetic field at high Galactic latitude. Furthermore, Planck and Hi emission data in combination indicate that most of the filamentary dust structures are in the cold neutral medium. The goal of this paper is to test whether these salient observational results, taken together, can account fully for the statistical properties of the dust polarization over a selected low column density region comprising 34% of the southern Galactic cap (b ≤ −30• ). To do this, we construct a dust model that incorporates Hi column density maps as tracers of the dust intensity structures and a phenomenological description of the Galactic magnetic field. By adjusting the parameters of the dust model, we were able to reproduce the Planck dust observations at 353 GHz in the selected region. Realistic simulations of the polarized dust emission enabled by such a dust model are useful for testing the accuracy of component separation methods, studying non-Gaussianity, and constraining the amount of decorrelation with frequency.

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The distribution of mean and fluctuating magnetic fields in the multiphase interstellar medium

Cited by 31 publications

References 20 publications

Topological signatures of interstellar magnetic fields – I. Betti numbers and persistence diagrams

Topological signatures of interstellar magnetic fields – I. Betti numbers and persistence diagrams

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

Modelling and simulation of large-scale polarized dust emission over the southern Galactic cap using the GASS Hi data

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