Are rotation curves in NGC 6946 and the Milky Way magnetically supported?

Abstract

Following the model of magnetically supported rotation of spiral galaxies, the inner disk rotation is dominated by gravity but magnetism is not negligible at radii where the rotation curve becomes flat, and indeed becomes dominant at very large radii. Values of the order of 1 $\mu$G, or even less, produce a centripetal force when the absolute value of the slope of the curve [$B_{\varphi }$, R] (azimuthal field strength versus radius) is less than $R^{-1}$. The $R^{-1}$-profile is called the critical profile. From this hypothesis, the following is to be expected: at large radii, a ``subcritical'' profile (slope flatter than $R^{-1}$); at still larger radii a $B_{\varphi }$-profile becoming asymptotically critical as the density becomes asymptotically vanishing. Recent observations of magnetic fields in NGC 6946 and the Milky Way are in very good agreement with these predictions. This magnetic alternative requires neither galactic dark matter (DM) nor modification of fundamental laws of physics, but it is not in conflict with these hypotheses, especially with the existence of cosmological cold dark matter (CDM).

11 pages, 2 figures, accepted for publication in Astron. Astrophys

References in corpus (4)

• The Cosmic Energy Inventory
• Global Dynamical Evolution of the ISM in Star Forming Galaxies - I. High Resolution 3D HD and MHD Simulations: Effect of the Magnetic Field
• Stellar Disk Truncations: Where do we stand ?
• Global Three-Dimensional MHD Simulations of Galactic Gaseous Disks: I. Amplification of Mean Magnetic Fields in Axisymmetric Gravitational Potential

Cited by in corpus (10)

• Magnetic Fields in Spiral Galaxies
• Cosmology with inhomogeneous magnetic fields
• Pulsar Rotation Measures and Large-scale Magnetic Field Reversals in the Galactic Disk
• Extragalactic Magnetism with SOFIA (Legacy Program) -- I: The magnetic field in the multi-phase interstellar medium of M51
• Magnetic fields and the outer rotation curve of M31
• Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- V: First results on the magnetic field orientation of galaxies
• Constraining the regular Galactic Magnetic Field with the 5-year WMAP polarization measurements at 22 GHz
• Cosmic ray knee and new physics at the TeV scale
• Galaxy rotation curves: the effect of j x B force
• Magnetic flux density from the relative circular motion of stars and partially ionized gas in the Galaxy mid-plane vicinity