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

Hanasz, M.; Otmianowska-Mazur, K.; Kowal, Grzegorz; Lesch, H.

doi:10.1002/asna.200610559

Cited by 25 publications

(43 citation statements)

References 25 publications

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“…In this model, the magnetic field, amplified initially, fades since the star formation stops. This star-forming activity was analyzed for spiral galaxies by Hanasz et al (2006), who measured a linear growth in the magnetic field. We can explain this by using a shorter simulation time (by about a factor of two) than in our case, but it may indicate that in irregulars the magnetic field is more easily expelled from the galaxy.…”

Section: Discussionmentioning

confidence: 99%

“…The t e of most models is in between 300 and 600 Myr. For spiral galaxies, Hanasz et al (2006Hanasz et al ( , 2009 found that the e-folding timescale is about 150-190 Myr. The difference between spirals and irregulars is probably caused by rotation, which is much more rapid in spirals.…”

Section: Discussionmentioning

confidence: 99%

“…The physical explanation of this process is difficult to establish because these galaxies rotate slowly, almost like a solid body. In this paper, we check how our model of cosmic-ray driven dynamo, which effectively describes spiral galaxies (Hanasz et al 2004(Hanasz et al , 2006(Hanasz et al , 2009, can be applied to irregular galaxies. In the present numerical experiment we attempt to answer how the model input parameters observed in irregulars (small gravitational potential, gas density, low rotation, and small shear) influence the magnetic fields within them.…”

Section: Introductionmentioning

confidence: 99%

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Cosmic-ray driven dynamo in the interstellar medium of irregular galaxies

Siejkowski¹,

Soida²,

Otmianowska-Mazur³

et al. 2010

A&A

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Context. Irregular galaxies are usually smaller and less massive than their spiral, S0, and elliptical counterparts. Radio observations indicate that a magnetic field is present in irregular galaxies whose value is similar to that in spiral galaxies. However, the conditions in the interstellar medium of an irregular galaxy are unfavorable for amplification of the magnetic field because of the slow rotation and low shearing rate. Aims. We investigate the cosmic-ray driven dynamo in the interstellar medium of an irregular galaxy. We study its efficiency under the conditions of slow rotation and weak shear. The star formation is also taken into account in our model and is parametrized by the frequency of explosions and modulations of activity. Methods. The numerical model includes a magnetohydrodynamical dynamo driven by cosmic rays that is injected into the interstellar medium by randomly exploding supernovae. In the model, we also include essential elements such as vertical gravity of the disk, differential rotation approximated by the shearing box, and resistivity leading to magnetic reconnection. Results. We find that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cosmic-ray driven dynamo in the interstellar medium of irregular galaxies

Siejkowski¹,

Soida²,

Otmianowska-Mazur³

et al. 2010

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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“…The CR-driven dynamo model consists of the following elements based on Hanasz et al (2006) and references therein. We assume: 390 H. Siejkowski et al • the cosmic ray component described by the diffusion-advection transport equation and we adopt anisotropic diffusion;…”

Section: Model Description and Initial Setupmentioning

confidence: 99%

3D model of magnetic fields evolution in dwarf irregular galaxies

Siejkowski¹,

Soida²,

Otmianowska-Mazur³

et al. 2010

Proc. IAU

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Abstract. Radio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.

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

Cited by 25 publications

References 25 publications

Cosmic-ray driven dynamo in the interstellar medium of irregular galaxies

Cosmic-ray driven dynamo in the interstellar medium of irregular galaxies

Cosmic-ray-driven dynamo in galactic disks

3D model of magnetic fields evolution in dwarf irregular galaxies

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