Cosmic-ray driven dynamo in galactic disks

Hanasz, M.; Otmianowska-Mazur, K.; Lesch, H.; Kowal, Grzegorz; Soida, M.; Wóltański, Dominik; Kowalik, Kacper; Pawłaszek, Rafał; Kulesza-Żydzik, Barbara

doi:10.1017/s1743921309031147

Cited by 9 publications

(9 citation statements)

References 37 publications

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“…The basic dominance of quadrupolar magnetic fields is also reproduced by more recent global simulations such as those of Gissinger et al (2009). However, the situation might be different in so-called cosmic-ray driven dynamos (see below), where the magnetic field could be preferentially dipolar with a reversal of the toroidal play about the midplane (Hanasz et al, 2009). The possibility of a significant dipolar component has also been found for the magnetic field of our Galaxy (Jansson & Farrar, 2012).…”

Section: Dominance Of Quadrupolar Modessupporting

confidence: 70%

Simulations of Galactic Dynamos

Brandenburg

2014

Astrophysics and Space Science Library

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We review our current understanding of galactic dynamo theory, paying particular attention to numerical simulations both of the mean-field equations and the original three-dimensional equations relevant to describing the magnetic field evolution for a turbulent flow. We emphasize the theoretical difficulties in explaining non-axisymmetric magnetic fields in galaxies and discuss the observational basis for such results in terms of rotation measure analysis. Next, we discuss nonlinear theory, the role of magnetic helicity conservation and magnetic helicity fluxes. This leads to the possibility that galactic magnetic fields may be bi-helical, with opposite signs of helicity and large and small length scales. We discuss their observational signatures and close by discussing the possibilities of explaining the origin of primordial magnetic fields.

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Section: Dominance Of Quadrupolar Modessupporting

confidence: 70%

Simulations of Galactic Dynamos

Brandenburg

2014

Astrophysics and Space Science Library

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“…Assuming these particles to be cosmic-ray (CR) particles raises the expectation of equipartition between the magnetic and the CR pressure (Hanasz et al 2009a). This equipartition was recently shown by Hanasz et al (2009b). More generally, in the framework of magnetohydrodynamics, any motion of the gas leading to the growth of the magnetic field will be suppressed by the magnetic field itself via the Lorentz force as soon as the magnetic energy gets comparable with the kinetic energy of the gas.…”

Section: Pressuresmentioning

confidence: 67%

Galactic ménage à trois: simulating magnetic fields in colliding galaxies

Kotarba

Lesch²,

Dolag

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present high‐resolution simulations of a multiple merger of three disc galaxies, including the evolution of magnetic fields, performed with the N‐body/smoothed particle hydrodynamics (SPH) code Gadget. For the first time, we embed the galaxies in a magnetized, low‐density medium, thus modelling an ambient intergalactic medium (IGM). The simulations include radiative cooling and a model for star formation and supernova feedback. Magnetohydrodynamics is followed using the SPH method. The progenitor discs have initial magnetic seed fields in the range 10−9–10−6 G and the IGM has initial fields of 10−12–10−9 G. The simulations are compared to a run excluding magnetic fields. We show that the propagation of interaction‐driven shocks depends significantly on the initial magnetic field strength. The shocks propagate faster in simulations with stronger initial field, suggesting that the shocks are supported by magnetic pressure. The Mach numbers of the shocks range from approximately M= 1.5 for the non‐magnetized case up to M= 6 for the highest initial magnetization, resulting in higher temperatures of the shock‐heated IGM gas. The magnetic field in the system saturates rapidly after the mergers at ∼10−6 G within the galaxies and ∼10−8 G in the IGM independent of the initial value. These field strengths agree with observed values and correspond to the equipartition value of the magnetic pressure with the turbulent pressure in the system. We also present synthetic radio and polarization maps for different phases of the evolution, showing that shocks driven by the interaction produce a high amount of polarized emission. These idealized simulations indicate that magnetic fields play an important role for the hydrodynamics of the IGM during galactic interactions. We also show that even weak seed fields are efficiently strengthened during multiple galactic mergers. This interaction‐driven amplification might have been a key process for the magnetization of the Universe.

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“…Cosmic-ray pressure can then build up until it reaches a value, presumably ∼P mag , that is high enough to break the magnetic confinement -for instance, via the Parker instability. Not only does this instability enable cosmic rays to escape from the galactic disk through the formation and rupture of giant magnetic loops, but it also leads to magnetic field amplification through enhanced dynamo action (Parker 1992;Hanasz et al 2004Hanasz et al , 2009). Both effects conspire to maintain cosmic-ray pressure comparable to magnetic pressure.…”

Section: Magnetic Field Strength: Critical Discussionmentioning

confidence: 99%

Interstellar magnetic fields in the Galactic center region

Ferrière¹

2009

A&A

107

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Aims. We seek to obtain a picture of the interstellar magnetic field in the Galactic center region that is as clear and complete as possible. Methods. We review the observational knowledge that has built up over the past 25 years on interstellar magnetic fields within ∼200 pc of the Galactic center. We then critically discuss the various theoretical interpretations and scenarios proposed to explain the existing observations. We also study the possible connections with the general Galactic magnetic field and describe the observational situation in external galaxies. Results. We propose a coherent picture of the magnetic field near the Galactic center, which reconciles some of the seemingly divergent views and which best accounts for the vast body of observations. Our main conclusions are the following. In the diffuse intercloud medium, the large-scale magnetic field is approximately poloidal and its value is generally close to equipartition with cosmic rays (∼10 μG), except in localized filaments where the field strength can reach ∼1 mG. In dense interstellar clouds, the magnetic field is approximately horizontal and its value is typically ∼1 mG.

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Cosmic-ray driven dynamo in galactic disks

Cited by 9 publications

References 37 publications

Simulations of Galactic Dynamos

Simulations of Galactic Dynamos

Galactic ménage à trois: simulating magnetic fields in colliding galaxies

Interstellar magnetic fields in the Galactic center region

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