Logarithmic magnetic-to-radiation pressure ratios plotted as a function of SFR surface density. Subsets of the sample are identified using different plotting symbols. The dashed line indicates a ratio of unity. The two sources having magnetic-to-radiation pressure ratios ≳5 are labeled: the nucleus of NGC 5866 hosts a known AGN (Moustakas et al. 2010); NGC 5194 Enuc. 11c may be an optically faint SNR (Maddox et al. 2007). The distribution of magnetic-to-radiation pressure ratios appears relatively flat as a function of SFR surface density.