Magnetic Fields are not ignorable in the dynamics of disks

Abstract

Magnetic fields are considered to be dominant when ${\epsilon }_B\ge {\epsilon }_K$, being ${\epsilon }_B=B^2/8\pi$ the magnetic energy density and ${\epsilon }_K=1/2\rho {\theta }^2$ the rotation energy density, for a conventional moderate B= 1 $\mu$G. They are considered to be negligible when ${\epsilon }_B<{\epsilon }_K$ for $B\sim 10\mu$G. With no assumption and no theoretical calculation, we show that magnetic fields cannot be ignored in the outer parts of a galaxy like the Milky Way and in the whole disk of a dwarf galaxy.

2 pages, 1 figure, for ASP Conference Series: "Galaxy Disks and Disk Galaxies", eds. J.G. Funes S.J. and E.M. Corsini