Magnetic fields: Impact on the rotation curve of the Galaxy

TL;DR

This study assesses how magnetic fields, cosmic rays, and gas pressure influence the rotation velocity of HI gas in the Milky Way, finding magnetic forces have minimal impact within 2Rsun.

Contribution

It provides a detailed modeling of magnetic and cosmic ray effects on galactic rotation, showing magnetic forces do not significantly alter HI gas velocities.

Findings

Magnetic forces are negligible in affecting HI rotation within 2Rsun.

Turbulent pressure and cosmic rays support the galactic disk radially.

Large-scale magnetic fields' support depends on local azimuthal field gradients.

Abstract

We quantify the effects of magnetic fields, cosmic rays and gas pressure on the rotational velocity of HI gas in the Milky Way, at galactic distances between Rsun and 2Rsun. 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 disk, the pressure by turbulent motions, cosmic rays and the tangled turbulent field provide radial support to the disk. Large-scale (ordered) magnetic fields may or may not provide support to the disk, 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 2Rsun.