paper

Magnetized galactic halos and velocity lags

arXiv:1603.02973 · doi:10.1093/mnras/stw590

Abstract

We present an analytic model of a magnetized galactic halo surrounding a Mestel gravitating disc. The magnetic field is taken to be in energy equipartition with the pressure dominant rotating halo gas ({\it not} with the cosmic rays), and the whole system is in a steady state. A more flexible `anisotropic equipartition' model is also explored. A definite pressure law is required to maintain the equilibrium, but the halo density is constant. The velocity/magnetic system is scale-free. The objective is to find the rotational velocity lag in such a halo. The magnetic field is not force-free so that angular momentum may be transported from the halo to the intergalactic medium. We find that the `X'-shaped structure observed for halo magnetic fields can be obtained together with a simple analytic formula for the rate of decline of the velocity with height . The formula also predicts the change in lag with radius, .

25 pages, 5 figures. Accepted (March 9, 2016) to Monthly Notices of the Royal Astronomical Society

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