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Hanasz, M.; Lesch, H.

doi:10.1023/a:1013853317182

Cited by 26 publications

(46 citation statements)

References 41 publications

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“…The galactic cosmic rays have a considerably broader distribution up to 20-30 kpc in galactic radius (Strong & Moskalenko 1998). The latter distribution suggests the existence of a self-regulation (valve) mechanism which removes the excess of cosmic rays above certain critical level of cosmic ray energy density (see Hanasz & Lesch 2001;Ptuskin 2001). This supports the model of Breitschwerdt et al (1993) who showed the possibility of an intense cosmic ray-driven galactic wind if the CR-energy density exceeds a critical value.…”

Section: Cosmic Rays and Dynamo Actionmentioning

confidence: 99%

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Strong magnetic fields and cosmic rays in very young galaxies

Lesch¹,

Hanasz²

2003

A&A

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Abstract. We present a scenario for efficient magnetization of very young galaxies about 0.5 gigayears after the Big-Bang by a cosmic ray-driven dynamo. These objects experience a phase of strong star formation during this first 10 9 years. We transfer the knowledge of the connection between star formation and the production rate of cosmic rays by supernova remnants to such high redshift objects. Since the supernova rate is a direct measure for the production rate of cosmic rays we conclude that very young galaxies must be strong sources of cosmic rays. The key argument of our model is the finding that magnetic fields and cosmic rays are dynamically coupled, i.e. a strong cosmic ray source contains strong magnetic fields since the relativistic particles drive an efficient dynamo in a galaxy via their buoyancy. We construct a phenomenological model of a dynamo driven by buoyancy of cosmic rays and show that if azimuthal shearing is strong enough the dynamo amplification timescale is close to the buoyancy timescale of the order of several 10 7 ÷ 10 8 yr. We predict that young galaxies are strongly magnetized and may contribute significantly to the gamma-ray-background.

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Section: Cosmic Rays and Dynamo Actionmentioning

confidence: 99%

“…The hot bubbles are supposed to be the source for the α-effect in conventional dynamos (Ferriere & Schmidt 2000), which are by a factor of 10 too slow for the amplification of the regular magnetic field component (Lesch & Camenzind 1994;Hanasz & Lesch 2001).…”

Section: Cosmic Rays and Dynamo Actionmentioning

confidence: 99%

Strong magnetic fields and cosmic rays in very young galaxies

Lesch¹,

Hanasz²

2003

A&A

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“…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%

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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“…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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Cited by 26 publications

References 41 publications

Strong magnetic fields and cosmic rays in very young galaxies

Strong magnetic fields and cosmic rays in very young galaxies

Cosmic-ray-driven dynamo in galactic disks

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

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