On the size and luminosity versus velocity dispersion correlations from the giant H II regions in the irregular galaxy NGC 4449

Here we present the size and luminosity versus velocity dispersion empirical correlations for the giant H II regions in the large irregular galaxy NGC 4449. We show that correlations only hold for nebulae with a surface brightness higher than 2 × 10³⁵ ergs s^-1 pc^-2 in Hα and with a supersonic single-line Gaussian profile. The exponents of the fits are consistent with virial mechanisms. A comparison with the results from other studies that have only used first-ranked giant H II regions from a variety of star-forming galaxies is also given.