Magnetic fields and star formation in low-mass Magellanic-type and peculiar galaxies

Abstract

We investigate how magnetic properties of Magellanic-type and perturbed objects are related to star-forming activity, galactic type, and mass. We present radio and magnetic properties of 5 Magellanic-type and 2 peculiar low-mass galaxies observed at 4.85 and/or 8.35 GHz with the Effelsberg 100-m telescope. The sample is extended to 17 objects by including 5 Magellanic-type galaxies and 5 dwarf ones. The radio emission of low-mass galaxies at 4.85/8.35 GHz is closely connected with their optical discs. The strengths of total magnetic field are within 5-9 \mu G, while the ordered fields reach 1-2 \mu G. The magnetic field strengths are well correlated with the surface density of SFR and manifest a power-law relation with an exponent of 0.25 extending a similar relation found for dwarf galaxies. The production of magnetic energy per supernova event is similar for all the various galaxies. It constitutes about 3% of the individual SN energy release. We show that the total magnetic field energy in galaxies is almost linearly related to the galactic gas mass, which indicates equipartition of the magnetic energy and the turbulent kinetic energy of the ISM. The Magellanic-type galaxies fit very well with the radio-infrared relation constructed for surface brightness of galaxies of various types, including bright spirals and interacting objects. We found that the typical far-infrared relation based on luminosity of galaxies is tighter and steeper but more likely to inherit a partial correlation from a tendency that larger objects are also more luminous. The thermal fractions, radio spectral indices, and magnetic field strengths of the Magellanic-type galaxies are between the values determined for spirals and dwarf galaxies. The confirmed magnetic field-star formation and radio-infrared relations for low-mass galaxies point to similar physical processes that must be at work in all galaxies.