2010MNRAS.402.1635R

We present Integral Field Spectroscopy (IFS) of NGC 595, one of the most luminous HII regions in M33. This type of observations allows us to study the variation of the principal emission-line ratios across the surface of the nebula. At each position of the field of view, we fit the main emission-line features of the spectrum within the spectral range of 3650-6990Å and create maps of the principal emission-line ratios for the total surface of the region. The extinction map derived from the Balmer decrement and the absorbed Hα luminosity show good spatial correlation with the 24µm emission from Spitzer. We also show here the capability of the IFS to study the existence of Wolf-Rayet (WR) stars, identifying the previously catalogued WR stars and detecting a new candidate towards the north of the region. The ionization structure of the region nicely follows the Hα shell morphology and is clearly related to the location of the central ionizing stars. The electron density distribution does not show strong variations within the HII region nor any trend with the Hα emission distribution. We study the behaviour within the HII region of several classical emission-line ratios proposed as metallicity calibrators: while [NII]/Hα and [NII]/[OIII] show important variations, the R₂₃ index is substantially constant across the surface of the nebula, despite the strong variation of the ionization parameter as a function of the radial distance from the ionizing stars. These results show the reliability in using the R₂₃ index to characterize the metallicity of HII regions even when only a fraction of the total area is covered by the observations.