Star-forming regions in the irregular galaxy NGC 4449: Determination of their integrated parameters

We present a study of the H II regions in the central area of the giant irr egular galaxy NGC 4449 based on observations taken on the William Herschel Telescope at the Rogue de los Muchachos observatory with the Taurus II Fabr y-Perot interferometer in the emission lines of H alpha and [O III] 5006.8. We show that the usual methods of determining sizes of H II regions are no t valid in this galaxy because of the high surface density of nebulae and t he presence of an intense diffuse luminosity over NGC 4449, so it has been necessary to develop a new method. The procedure we have used allows integr ated parameters of H rr regions (radius, luminosity, radial velocity, and v elocity dispersion) to be obtained with greater objectivity and precision t han with other methods. The technique proposed here can be extended to para meterize giant H II regions in galaxies in general and to resolve the probl em of the large uncertainties associated with previous methods in character izing star-forming regions in Magellanic irregular galaxies.