Faraday Dispersion Functions of Galaxies

Ideguchi, Shinsuke; Tashiro, Yuichi; Akahori, Takuya; Takahashi, Keitaro; Ryu, Dongsu

doi:10.1088/0004-637x/792/1/51

Cited by 24 publications

(41 citation statements)

References 36 publications

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“…As in Ideguchi et al (2014), the width σ, skewness γ s , and kurtosis γ k of F(f) were calculated (see Equations (3)- (5)). Figure 2 shows the scattered distributions of these shapecharacterizing parameters with B coh = 0 μG for N ⊥ = 1, 9, 100, and 900; 800 realizations for each value of N ⊥ are shown.…”

Section: Convergencementioning

confidence: 99%

“…On the other hand, γ s and γ k exhibit behaviors that are too complicated. In summary, in Ideguchi et al (2014), F(f) was obtained with a realistic model, but its behavior was not easy to interpret, mainly due to the turbulent field.…”

Section: Introductionmentioning

confidence: 95%

“…While it would be straightforward to estimate, for instance, the number of sources of synchrotron radiation and their Faraday depths, the Faraday spectrum could be used to obtain more information. The properties of F(f) were previously studied (e.g., Bell et al 2011;Frick et al 2011;Beck et al 2012;Ideguchi et al 2014). For instance, the characteristic features in F(f) caused by various configurations of the large-scale LOS magnetic field such as field reversal were examined using simple models.…”

Section: Introductionmentioning

confidence: 99%

“…Previously, in Ideguchi et al (2014), we studied the F(f) of face-on galaxies, using a realistic model for the Milky Way (Akahori et al 2013). The model included the global, regular component of the magnetic field, based on observations, as well as the turbulent component, constructed with the data from magnetohydrodynamic turbulence simulations.…”

Section: Introductionmentioning

confidence: 99%

“…We also consider the turbulent field represented by power-law spectra. We then examine how F(f) obtained along "multiple LOSs" can be used to study the vertical magnetic field of face-on spiral galaxies, inspired by the result of Ideguchi et al (2014) that F(f) becomes smoother and thus easier to interpret with a larger number of LOSs. We regard this work as the first step in finding a practical way to extract the magnetic field information from the Faraday spectrum.…”

Section: Introductionmentioning

confidence: 99%

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Study of the Vertical Magnetic Field in Face-on Galaxies Using Faraday Tomography

Ideguchi

Tashiro

Akahori

et al. 2017

ApJ

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Faraday tomography allows astronomers to probe the distribution of the magnetic field along the line of sight (LOS), but that can be achieved only after the Faraday spectrum is interpreted. However, the interpretation is not straightforward, mainly because the Faraday spectrum is complicated due to a turbulent magnetic field; it ruins the one-to-one relation between the Faraday depth and the physical depth, and appears as many small-scale features in the Faraday spectrum. In this paper, by employing "simple toy models" for the magnetic field, we describe numerically as well as analytically the characteristic properties of the Faraday spectrum. We show that the Faraday spectrum along "multiple LOSs" can be used to extract the global properties of the magnetic field. Specifically, considering face-on spiral galaxies and modeling turbulent magnetic field as a random field with a single coherence length, we numerically calculate the Faraday spectrum along a number of LOSs and its shape-characterizing parameters, that is, the moments. When multiple LOSs cover a region of (10 coherence length) 2 , the shape of the Faraday spectrum becomes smooth and the shape-characterizing parameters are well specified. With the Faraday spectrum constructed as a sum of Gaussian functions with different means and variances, we analytically show that the parameters are expressed in terms of the regular and turbulent components of the LOS magnetic field and the coherence length. We also consider the turbulent magnetic field modeled with a power-law spectrum, and study how the magnetic field is revealed in the Faraday spectrum. Our work suggests a way to obtain information on the magnetic field from a Faraday tomography study.

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Section: Convergencementioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Study of the Vertical Magnetic Field in Face-on Galaxies Using Faraday Tomography

Ideguchi

Tashiro

Akahori

et al. 2017

ApJ

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Magnetic fields in spiral galaxies

Beck¹

2015

Astron Astrophys Rev

368

269

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Radio synchrotron emission, its polarization and Faraday rotation of the polarization angle are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 μG) and in central starburst regions (50-100 μG). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15 μG) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the intergalactic medium.-Faraday rotation measures of the diffuse polarized radio emission from galaxy disks reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by mean-field dynamos. "Magnetic arms" between gaseous spiral arms may also be products of dynamo action, but need a stable spiral pattern to develop. Helically twisted field loops winding around spiral arms were found in two galaxies so far. Large-scale field reversals, like the one found in the Milky Way, could not yet be detected in external galaxies. In radio halos around edgeon galaxies, ordered magnetic fields with X-shaped patterns are observed. The origin and evolution of cosmic magnetic fields, in particular their first occurrence in young

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Resolved magnetic structures in the disk-halo interface of NGC 628

Mulcahy

Beck

Heald

2017

A&A

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Context. Magnetic fields are essential to fully understand the interstellar medium and its role in the disk-halo interface of galaxies is still poorly understood. Star formation is known to expel hot gas vertically into the halo and these outflows have important consequences for mean-field dynamo theory in that they can be efficient in removing magnetic helicity. Aims. We aim to probe the vertical magnetic field and enhance our understanding of the disk-halo interaction of galaxies. Studying a face-on galaxy is essential so that the magnetic field components can be separated in 3D. Methods. We perform new observations of the nearby face-on spiral galaxy NGC 628 with the Karl G. Jansky Very Large Array (JVLA) at S -band (2.6-3.6 GHz effective bandwidth) and the Effelsberg 100-m telescope at frequencies of 2.6 GHz and 8.35 GHz with a bandwidth of 80 MHz and 1.1 GHz, respectively. Owing to the large bandwidth of the JVLA receiving system, we obtain some of the most sensitive radio continuum images in both total and linearly polarised intensity of any external galaxy observed so far. Results. The application of rotation measures synthesis to the interferometric polarisation data over this large bandwidth provides high-quality images of Faraday depth and polarisation angle from which we obtained evidence for drivers of magnetic turbulence in the disk-halo connection. Such drivers include a superbubble detected via a significant Faraday depth gradient coinciding with a H I hole. We observe an azimuthal periodic pattern in Faraday depth with a pattern wavelength of 3.7 ± 0.1 kpc, indicating Parker instabilities. The lack of a significant anti-correlation between Faraday depth and magnetic pitch angle indicates that these loops are vertical in nature with little helical twisting, unlike in IC 342. We find that the magnetic pitch angle is systematically larger than the morphological pitch angle of the polarisation arms which gives evidence for the action of a large-scale dynamo where the regular magnetic field is not coupled to the gas flow and obtains a significant radial component. We additionally discover a lone region of ordered magnetic field to the north of the galaxy with a high degree of polarisation and a small pitch angle, a feature that has not been observed in any other galaxy so far and is possibly caused by an asymmetric H I hole. Conclusions. Until now NGC 628 has been relatively unexplored in radio continuum but with its extended H I disk and lack of active star formation in its central region has produced a wealth of interesting magnetic phenomena. We observe evidence for two drivers of magnetic turbulence in the disk-halo connection of NGC 628, namely, Parker instabilities and superbubbles.

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Faraday Dispersion Functions of Galaxies

Cited by 24 publications

References 36 publications

Study of the Vertical Magnetic Field in Face-on Galaxies Using Faraday Tomography

Study of the Vertical Magnetic Field in Face-on Galaxies Using Faraday Tomography

Magnetic fields in spiral galaxies

Resolved magnetic structures in the disk-halo interface of NGC 628

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