2013MNRAS.433.2172S

We quantify the effects of magnetic fields, cosmic rays and gas pressure on the rotational velocity of Hi gas in the Milky Way, at Galactocentric distances between R☉ and 2R☉. The magnetic field is modelled by two components: a mainly azimuthal magnetic component and a small-scale tangled field. We construct a range of plausible axisymmetric models consistent with the strength of the total magnetic field as inferred from radio synchrotron data. In a realistic Galactic disc, the pressure by turbulent motions, cosmic rays and the tangled turbulent field provides radial support to the disc. Large-scale (ordered) magnetic fields may or may not provide support to the disc, depending on the local radial gradient of the azimuthal field. We show that for observationally constrained models, magnetic forces cannot appreciably alter the tangential velocity of Hi gas within a galactic distance of 2R☉.