Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetized galactic halos and velocity lags   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 $z$. The formula also predicts the change in lag with
radius, $r$.

15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn