Upper limits to magnetic fields in the outskirts of galaxies

Abstract

Based on CO(2-1) public data, we study the monoxide oxygen gas excitation conditions and the magnetic field strength of four spiral galaxies. For the galaxy outskirts, we found kinetic temperatures in the range of ≲35-38 K, CO column densities ≲1015-1016 cm-2, and H2 masses ≲4 × 106-6 × 108 M⊙. An H2 density ≲103 cm-3 is suitable to explain the 2σ upper limits of the CO(2-1) line intensity. We constrain the magnetic field strength for our sample of spiral galaxies and their outskirts by using their masses and H2 densities to evaluate a simplified magneto-hydrodynamic equation. Our estimations provide values for the magnetic field strength on the order of ≲6-31 μG.