Strong magnetic fields and cosmic rays in very young galaxies

Lesch, H.; Hanasz, M.

doi:10.1051/0004-6361:20030212

Cited by 24 publications

(17 citation statements)

References 52 publications

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“…A striking property of the mean magnetic-field configuration is the almost exact coincidence of peaks between the oppositely-directed radial and azimuthal field components. This feature resembles the standard picture of an αω-dynamo: the azimuthal, mean magnetic-component is generated from the radial one and vice versa (see Lesch & Hanasz 2003, for a correspondingly simple analytical model).…”

Section: Resultssupporting

confidence: 56%

“…The idea relies on two ingredients: (1) cosmic rays (CR) continuously supplied to the disk by supernova (SN) remnants and (2) fast magnetic reconnection, which operates in current sheets and enables the dissipation and relaxation of the random magnetic-field components at the limit of vanishing resistivity. In the past decade, we have investigated the different elements, physical properties, and consequences of Parker's idea and scenario by means of analytical calculations and numerical simulations (Hanasz & Lesch 1993, 1997, 1998, 2000, 2001, 2003aHanasz et al 2002Hanasz et al , 2004Hanasz et al , 2006Lesch & Hanasz 2003;Otmianowska-Mazur 2003;Otmianowska-Mazur et al 2007;Kowal et al 2003Kowal et al , 2006 The first complete 3D numerical model of the CR-driven dynamo was developed by Hanasz et al (2004Hanasz et al ( , 2006. In this paper, we perform a parameter study of the CR-driven dynamo model by examining the dependence of magnetic-field amplification on magnetic diffusivity, supernova rate determining the CR injection rate, temporal modulation of SN activity, grid resolution, and CR diffusion coefficients.…”

Section: Introductionmentioning

confidence: 99%

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Cosmic-ray-driven dynamo in galactic disks

Hanasz¹,

Otmianowska-Mazur

Kowal

et al. 2009

A&A

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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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Section: Resultssupporting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Cosmic-ray-driven dynamo in galactic disks

Hanasz¹,

Otmianowska-Mazur

Kowal

et al. 2009

A&A

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“…With its growth time of order the rotation time, the MRI is fast, with e-folding times below 0.1 Gyr. The observation of Faraday rotation of highredshift objects by Athreya et al (1998) and Carilli & Taylor (2002) seems to indicate that such short growth times really exist (Lesch & Hanasz 2003).…”

Section: Introductionmentioning

confidence: 93%

Seed fields for galactic dynamos by the magnetorotational instability

Kitchatinov

Rüdiger

2004

A&A

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Abstract.A linear but global numerical model for the magnetorotational instability (MRI) in a disk geometry is considered to estimate the instability parameters for galaxies. Similarity rules suggested by a local analysis are applied to reveal a universal behavior of the results of global calculations for large magnetic Prandtl numbers. The findings are used to estimate the MRI characteristics for galaxies with their very large magnetic Prandtl numbers which cannot be attained in any numerical simulations. The resulting minimum field for the instability, B min 10 −25 G, is small compared to any seed fields currently discussed. The growth times of MRI are estimated to be on the order of the rotation period of the inner rigidly-rotating core, i.e. ∼100 Myr. Global MRI excites preferentially magnetic field modes of quadrupolar symmetry.

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“…Corresponding author: mhanasz@astri.uni.torun.pl the last decade we have investigated the different physical properties and consequences of Parker's scenario by means of analytical calculations and numerical simulations (Hanasz & Lesch 1993, 1997, 1998, 2000, 2001, 2003a, 2003bHanasz et al 2002Hanasz et al , 2004Hanasz et al , 2005Lesch & Hanasz 2003;Otmianowska-Mazur 2003;Kowal et al 2003Kowal et al , 2005. In this paper we report a further development of the CRdriven dynamo by focusing on the role of resistivity, of the SN rate, and of a modulation of the SN rate by galactic spiral arms.…”

Section: Introductionmentioning

confidence: 99%

Cosmic ray driven dynamo in galactic disks: effects of resistivity, SN rate and spiral arms

Hanasz¹,

Otmianowska-Mazur

Kowal

et al. 2006

Astron Nachr

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We present a further development of the first numerical model of the magnetohydrodynamical dynamo, driven by cosmic rays in the interstellar medium (Hanasz et al. 2004). The cosmic rays are produced in randomly occurring supernova remnants. Our model is described by equations of magnetohydrodynamics supplemented with the diffusion-advection equation governing the propagation of cosmic rays. The other essential elements of the model are: vertical gravity of the disk, differential rotation and resistivity leading to reconnection of magnetic field lines. We obtain amplification of the large-scale magnetic field on a timescale of galactic rotation. The model represents a kind of fast, cosmic ray driven galactic dynamo proposed by Parker (1992). The amplification of the large-scale magnetic field results from the buoyancy of the cosmic ray component in the interstellar medium. We describe five models characterized by different resistivity magnitudes, supply rates of cosmic rays and discuss in more detail a model with periodic SN activity, which mimics the presence of spiral arms in the disk. We find that both the resistivity and spiral arms enhance the efficiency of the cosmic-ray dynamo. The timescale of magnetic field amplification in this model is as short as 140 Myr.

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Strong magnetic fields and cosmic rays in very young galaxies

Cited by 24 publications

References 52 publications

Cosmic-ray-driven dynamo in galactic disks

Cosmic-ray-driven dynamo in galactic disks

Seed fields for galactic dynamos by the magnetorotational instability

Cosmic ray driven dynamo in galactic disks: effects of resistivity, SN rate and spiral arms

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