EDP Sciences
Free access
Volume 445, Number 3, January III 2006
Page(s) 915 - 929
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20053582

A&A 445, 915-929 (2006)
DOI: 10.1051/0004-6361:20053582

Dynamo coefficients in Parker unstable disks with cosmic rays and shear

The new methods of estimation
G. Kowal1, K. Otmianowska-Mazur1 and M. Hanasz2

1  Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
    e-mail: kowal@oa.uj.edu.pl
2  Torun Centre for Astronomy, Nicholas Copernicus University, 87-148 Piwnice/Torun, Poland

(Received 7 June 2005 / Accepted 18 July 2005 )

We report a three-dimensional (3D) numerical model of the Parker instability with cosmic rays and shear in a galactic disk and compute the components of the dynamo coefficients $\alpha$ and $\beta$ from the electromotive forces obtained from simulations. For the first time we apply well-known statistical procedures to fit the modeled electromotive forces in terms of the dynamo tensors. We compare our results with kinematic and other methods of dynamo coefficient estimation. Although we do not solve all problems with the physical interpretation of the dynamo tensors we find that the presented methods give us the ability to compute them with the desired statistical quality. The obtained values of $\alpha_{xx}$ (along the radial direction in galaxy) and $\alpha_{zz}$ are of the order of a few km s-1 while the value of $\alpha_{yy}$ (along the azimuthal direction) is one or two orders of magnitude smaller.

Key words: galaxies: ISM -- galaxies: magnetic fields -- methods: numerical -- methods: data analysis

© ESO 2006