Magnetic Fields in Irregular Galaxies

Kepley, Amanda A.; Muehle, S.; Wilcots, Eric M.; Everett, J. E.; Zweibel, Ellen G.; Robishaw, Timothy; Heiles, Carl

doi:10.1007/978-1-4020-6933-8_15

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“…4). The nonrotating case has been discussed by us previously (Yousef et al 2008) and is relevant to nonrotating systems as well as systems where one expects the shear to be stronger than the rotation (one good astrophysical example is irregular galaxies, where large-scale magnetic fields are found in the absence of strong overall rotation; 1 see Chyży et al 2000Chyży et al , 2003Gaensler et al 2005;Kepley et al 2007). The case of Keplerian rotation corresponds to the local shearing-sheet model of thin accretion disks, for which the angular velocity decreases radially ∝ R −3/2 .…”

Section: Model and Numerical Set Upmentioning

confidence: 99%

Numerical experiments on dynamo action in sheared and rotating turbulence

et al. 2008

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Numerical simulations of forced turbulence in elongated shearing boxes are carried out to demonstrate that a nonhelical turbulence in conjunction with a linear shear can give rise to a mean-field dynamo. Exponential growth of magnetic field at scales larger than the outer (forcing) scale of the turbulence is found. Over a range of values of the shearing rate S spanning approximately two orders of magnitude, the growth rate of the magnetic field is proportional to the imposed shear, γ ∝ S, while the characteristic spatial scale of the field is lB ∝ S −1/2 . The effect is quite general: earlier results for the nonrotating case by Yousef et al. (2008) are extended to shearing boxes with Keplerian rotation; it is also shown that the shear dynamo mechanism operates both below and above the threshold for the fluctuation dynamo. The apparently generic nature of the shear dynamo effect makes it an attractive object of study for the purpose of understanding the generation of magnetic fields in astrophysical systems.

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