Chang-Es

Stein, Y.; Dettmar, R.‐J.; Irwin, Judith A.; Beck, Rainer; Weżgowiec, M.; Miskolczi, A.; Krause, M.; Heesen, V.; Wiegert, Theresa; Heald, G.; Walterbos, R. A. M.; Li, J.-T.; Soida, M.

doi:10.1051/0004-6361/201834515

Cited by 37 publications

(59 citation statements)

References 64 publications

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“…Due to the lack of good RM data, we cannot say much about the z-component of the regular field nor about field reversals at certain heights above the disc plane. A few edge-on galaxies, NGC 4631 [83], NGC 4666 [68], and other cases in the CHANG-ES sample show strong B reg,z in the halo. The regular field in the halo of NGC 4631 is coherent over about 2 kpc in height, reverses on a scale of about 2 kpc in radius, and is about 4 µG strong, compared to the average strength of the total field in the disc of about 9 µG.…”

Section: Observationsmentioning

confidence: 92%

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 Based on archival and previously unpublished data, we then compile various important properties of galactic magnetic fields for nearby spiral galaxies.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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Section: Observationsmentioning

confidence: 92%

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

et al. 2019

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“…At later stages the radial magnetic field components change the sign several times as function of the radius. From observations this is known as a first indicator for ongoing dynamo action(Stein et al 2019). We show the dependence of the radial and the toroidal magnetic field component as a function of the disc scale height for six different points in time, t=1 Gyr (blue), t=1.5 Gyr (orange), t=2 Gyr (green), t=2.5 Gyr (red), t=3 Gyr (purple) and t=3.5 Gyr (brown)…”

mentioning

confidence: 99%

On the origin of magnetic driven winds and the structure of the galactic dynamo in isolated galaxies

Steinwandel

Dolag

Lesch³

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We investigate the build-up of the galactic dynamo and subsequently the origin of a magnetic driven outflow. We use a setup of an isolated disc galaxy with a realistic circum-galactic medium (CGM). We find good agreement of the galactic dynamo with theoretical and observational predictions from the radial and toroidal components of the magnetic field as function of radius and disc scale height. We find several field reversals indicating dipole structure at early times and quadrupole structure at late times. Together with the magnetic pitch angle and the dynamo control parameters R α , R ω and D we present strong evidence for an α 2 -Ω dynamo. The formation of a bar in the centre leads to further amplification of the magnetic field via adiabatic compression which subsequently drives an outflow. Due to the Parker-Instability the magnetic field lines rise to the edge of the disc, break out and expand freely in the CGM driven by the magnetic pressure. Finally, we investigate the correlation between magnetic field and star formation rate. Globally, we find that the magnetic field is increasing as function of the star formation rate surface density with a slope between 0.3 and 0.45 in good agreement with predictions from theory and observations. Locally, we find that the magnetic field can decrease while star formation increases. We find that this effect is correlated with the diffusion of magnetic field from the spiral arms to the inter-arm regions which we explicitly include by solving the induction equation and accounting for non-linear terms.

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“…medium for a large number of sources in a much reduced amount of observing time. Broad-band spectro-polarimetry has played a crucial role in unveiling the properties of magnetic fields in nearby galaxies [1][2][3], in high redshift galaxies [4,5], in active galactic nuclei [AGN; 6-8] and the intergalactic medium [9]. In order to physically interpret such data, the technique of Faraday rotation measure (RM) synthesis [10,11] and direct fitting of the Stokes Q and U spectra of a polarized source with models of the magneto-ionic media, known as Stokes Q, U fitting [6,12,13] have been developed.…”

Section: Of 30mentioning

confidence: 99%

“…We generated such a medium on a 512 × 512 × 512 pixel 3 mesh and assumed the mesh points to be separated by 1 pc. Therefore, the physical volume of the simulated uniform medium is 512 × 512 × 512 pc 3 . The values of the physical quantities used to simulate a uniform slab are listed in Table 1.…”

Section: Uniform Slab Modelmentioning

confidence: 99%

An In-Depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations

et al. 2019

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In this paper we present a detailed analysis of the Faraday depth (FD) spectrum and its clean components obtained through the application of the commonly used technique of Faraday rotation measure synthesis to analyze spectro-polarimetric data. In order to directly compare the Faraday depth spectrum with physical properties of a magneto-ionic medium, we generated synthetic broad-bandwidth spectro-polarimetric observations from magnetohydrodynamic (MHD) simulations of a transonic, isothermal, compressible turbulent medium. We find that correlated magnetic field structures give rise to a combination of spiky, localized peaks at certain FD values, and broad structures in the FD spectrum. Although the majority of these spiky FD structures appear narrow, giving an impression of a Faraday thin medium, we show that they arise from strong synchrotron emissivity at that FD. Strong emissivity at a FD can arise because of both strong spatially-local polarized synchrotron emissivity at a FD or accumulation of weaker emissions along the distance through a medium that have Faraday depths within half the width of the rotation measure spread function. Such a complex Faraday depth spectrum is a natural consequence of MHD turbulence when the lines of sight pass through a few turbulent cells. This therefore complicates the convention of attributing narrow FD peaks to presence of a Faraday rotating medium along the line of sight. Our work shows that it is difficult to extract the FD along a line of sight from the Faraday depth spectrum using standard methods for a turbulent medium in which synchrotron emission and Faraday rotation occur simultaneously. of 30medium for a large number of sources in a much reduced amount of observing time. Broad-band spectro-polarimetry has played a crucial role in unveiling the properties of magnetic fields in nearby galaxies [1][2][3], in high redshift galaxies [4,5], in active galactic nuclei [AGN; 6-8] and the intergalactic medium [9]. In order to physically interpret such data, the technique of Faraday rotation measure (RM) synthesis [10,11] and direct fitting of the Stokes Q and U spectra of a polarized source with models of the magneto-ionic media, known as Stokes Q, U fitting [6,12,13] have been developed. It is often not straightforward to interpret the results from these techniques and connect them to the physical properties of the magnetized plasmas being investigated [14].Currently, several large-scale spectro-polarimetric campaigns are underway, mostly in the 1 to 5 GHz frequency range. On one hand, dedicated surveys with interferometers are being conducted to study the broad-band polarization properties of millions of extragalactic sources. For example, the Karl G. Jansky Very Large Array Sky Survey [VLASS; 15,16], the Polarization Sky Survey of the Universe's Magnetism [POSSUM; 17], the QU Observations at Cm wavelength with Km baselines using ATCA 1 (QUOCKA), the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey [18], and the recent LOFAR Two-meter Sky Survey [L...

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Chang-Es

Cited by 37 publications

References 64 publications

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

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

On the origin of magnetic driven winds and the structure of the galactic dynamo in isolated galaxies

An In-Depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations

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