Observations in the line of Hα and of [OIII] λ5007 of the galaxy NGC 4449 taken at the William Herschel Telescope of the Observatorio del Roque de los Muchachos with TAURUS-2, a Fabry-Perot interferometer, are being used to study the correlation between the diameter or flux and the velocity dispersion of its HII regions. Two different catalogues of HII regions are being compared. In the first we consider each flux relative maximum as a differentiated HII region, while in the second sample we use kinematical criteria to identify the different regions.

Introduction

In 1981, Terlevich and Melnick established a correlation between the diameter or the luminosity of giant HII regions and the turbulent width of their emission lines, which represented a chance to improve present extragalactic distance estimations. To study the possible existence of similar correlations for HII regions in a single galaxy, we have chosen NGC 4449, a giant irregular type I galaxy. It is located 5 Mpc away from the Milky Way and is very rich in HII regions. New criteria to identify HII regions are explored and compared with the samples and measurements already present in the literature. Detailed information will be presented in Fuentes-Masip et al. (1994, in preparation).

Data analysis

The product of the calibrated Fabry-Perot observations was a three dimensional set where the X-Y axes were the spatial coordinates, and the Z axis was wavelength calibrated (the dispersion direction).