Incorporation of cosmic ray transport into the ZEUS MHD code

Hanasz, M.; Lesch, H.

doi:10.1051/0004-6361:20031433

Cited by 84 publications

(89 citation statements)

References 32 publications

(31 reference statements)

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“…The cosmic ray (CR) component is described by the diffusion-advection transport equation in terms of fluid approximation following Schlickeiser & Lerche (1985) and Hanasz & Lesch (2003). We related the CR pressure to the CR energy density e cr via the adiabatic CR index, that is p cr ≡ (γ cr − 1)e cr and γ cr = 14/9 adopted from Ryu et al (2003).…”

Section: Numerical Model and Setupmentioning

confidence: 99%

3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

Siejkowski

Otmianowska-Mazur

Soida

et al. 2014

A&A

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Context. Star-forming dwarf galaxies can be seen as the local proxies of the high-redshift building blocks of more massive galaxies according to the current paradigm of the hierarchical galaxy formation. They are low-mass objects, and therefore their rotation speed is very low. Several galaxies are observed to show quite strong magnetic fields. These cases of strong ordered magnetic fields seem to correlate with a high, but not extremely high, star formation rate. Aims. We investigate whether these magnetic fields could be generated by the cosmic-ray-driven dynamo. The environment of a dwarf galaxy is unfavourable for the large-scale dynamo action because of the very slow rotation that is required to create the regular component of the magnetic field. Methods. We built a 3D global model of a dwarf galaxy that consists of two gravitational components: the stars and the dark-matter halo described by the purely phenomenological profile proposed previously. We solved a system of magnetohydrodynamic equations that include an additional cosmic-ray component described by the fluid approximation. Results. We found that the cosmic-ray-driven dynamo can amplify the magnetic field with an exponential growth rate. The e-folding time is correlated with the initial rotation speed. The final mean value of the azimuthal flux for our models is on the order of few µG and the system reaches its equipartition level. The results indicate that the cosmic-ray-driven dynamo is a process that can explain the magnetic fields in dwarf galaxies.

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Section: Numerical Model and Setupmentioning

confidence: 99%

3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

Siejkowski

Otmianowska-Mazur

Soida

et al. 2014

A&A

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“…(1) the cosmic-ray component, a relativistic gas, which is described by the diffusion-advection transport equation (see Hanasz & Lesch 2003b, for details of the numerical algorithm). The typical values of the diffusion coefficient found by modeling CR data (see e.g.…”

Section: Description Of the Modelmentioning

confidence: 99%

Cosmic-ray-driven dynamo in galactic disks

Hanasz¹,

Otmianowska-Mazur

Kowal

et al. 2009

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Aims. We present a parameter study of the magnetohydrodynamical-dynamo driven by cosmic rays in the interstellar medium (ISM), focusing on the efficiency of magnetic-field amplification and the issue of energy equipartition between magnetic, kinetic, and cosmicray (CR) energies. Methods. We perform numerical CR-MHD simulations of the ISM using an extended version of ZEUS-3D code in the shearingbox approximation and taking into account the presence of Ohmic resistivity, tidal forces, and vertical disk gravity. CRs are supplied in randomly-distributed supernova (SN) remnants and are described by the diffusion-advection equation, which incorporates an anisotropic diffusion tensor. Results. The azimuthal magnetic flux and total magnetic energy are amplified in the majority of models depending on a particular choice of model parameters. We find that the most favorable conditions for magnetic-field amplification correspond to magnetic diffusivity of the order of 3 × 10 25 cm 2 s −1 , SN rates close to those observed in the Milky Way, periodic SN activity corresponding to spiral arms, and highly anisotropic and field-aligned CR diffusion. The rate of magnetic-field amplification is relatively insensitive to the magnitude of SN rates spanning a range of 10% to 100% of realistic values. The timescale of magnetic-field amplification in the most favorable conditions is 150 Myr, at a galactocentric radius equal to 5 kpc, which is close to the timescale of galactic rotation. The final magnetic-field energies reached in the efficient amplification cases fluctuate near equipartition with the gas kinetic energy. In all models CR energy exceeds the equipartition values by a least an order of magnitude, in contrast to the commonly expected equipartition. We suggest that the excess of cosmic rays in numerical models can be attributed to the fact that the shearing box does not permit cosmic rays to leave the system along the horizontal magnetic field, as may be the case for true galaxies.

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“…In Galactic propagation studies, however, anisotropic diffusion of CRs has been investigated only for basic magnetic field configurations of partly localized applicability; see, e.g., Chuvilgin & Ptuskin (1993), Breitschwerdt et al (2002), Snodin et al (2006) and references therein. While the latter authors were interested in the consequences of anisotropic diffusion for energy equipartition, Hanasz & Lesch (2003) and Ryu et al (2003) analyzed its importance for the Parker instability.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic diffusion of Galactic cosmic ray protons and their steady-state azimuthal distribution

Effenberger

Fichtner

Scherer

et al. 2012

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Galactic transport models for cosmic rays involve the diffusive motion of these particles in the interstellar medium. Owing to the large-scale structured Galactic magnetic field, this diffusion is anisotropic with respect to the local field direction. We included this transport effect along with continuous loss processes in a quantitative model of Galactic propagation for cosmic ray protons that is based on stochastic differential equations. We calculated energy spectra at different positions along the Sun's Galactic orbit and compared them to the isotropic diffusion case. The results show that a larger amplitude of variation and different spectral shapes are obtained in the introduced anisotropic diffusion scenario, which in turn emphasizes the need for accurate Galactic magnetic field models.

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Incorporation of cosmic ray transport into the ZEUS MHD code

Cited by 84 publications

References 32 publications

3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies

Cosmic-ray-driven dynamo in galactic disks

Anisotropic diffusion of Galactic cosmic ray protons and their steady-state azimuthal distribution

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