On the size and luminosity versus velocity dispersion correlations from the giant HII 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 x 10(35) ergs s(-1) pc(-2) in H alpha 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.