Spatially resolved study of the physical properties of the ionized gas
  in NGC 595
  We present Integral Field Spectroscopy (IFS) of NGC 595, one of the most
luminous HII regions in M33. This type of observations allows studying 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 3650-6990A, 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 H-alpha
luminosity show good spatial correlation with the 24 micron 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 H-alpha 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 H-alpha emission distribution. We study the behaviour within
the HII region of several classical emission-line ratios proposed as
metallicity calibrators: while [NII]/Ha 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.
