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 empirica l 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 brigh tness higher than 2 x 10(35) ergs s(-1) pc(-2) in H alpha and with a supers onic single-line Gaussian profile. The exponents of the fits are consistent with virial mechanisms. A comparison with the results from other studies t hat have only used first-ranked giant H II regions from a variety of star-f orming galaxies is also given.