Spatially resolved integral field spectroscopy of the ionized gas in IZw18<SUP>★</SUP>

We present a detailed 2D study of the ionized ISM of IZw18 using new PMAS-IFU optical observations. IZw18 is a high-ionization galaxy which is among the most metal-poor starbursts in the local Universe. This makes IZw18 a local benchmark for understanding the properties most closely resembling those prevailing at distant starbursts. Our IFU-aperture (̃ 1.4 × 1.4 kpc<SUP>2</SUP>) samples the entire IZw18 main body and an extended region of its ionized gas. Maps of relevant emission lines and emission line ratios show that higher-excitation gas is preferentially located close to the NW knot and thereabouts. We detect a Wolf-Rayet feature near the NW knot. We derive spatially resolved and integrated physical-chemical properties for the ionized gas in IZw18. We find no dependence between the metallicity-indicator R<SUB>23</SUB> and the ionization parameter (as traced by [OIII]/[OII]) across IZw18. Over ̃ 0.30 kpc<SUP>2</SUP>, using the [OIII]λ4363 line, we compute T<SUB>e</SUB>[OIII] values (̃ 15,000 - 25,000 K), and oxygen abundances are derived from the direct determinations of T<SUB>e</SUB>[OIII]. More than 70% of the higher-T<SUB>e</SUB>[OIII] (≳ 22,000 K) spaxels are HeIIλ4686-emitting spaxels too. From a statistical analysis, we study the presence of variations in the ISM physical-chemical properties. A galaxy-wide homogeneity, across hundreds of parsecs, is seen in O/H. Based on spaxel-by-spaxel measurements, the error-weighted mean of 12 + log(O/H) = 7.11 ± 0.01 is taken as the representative O/H for IZw18. Aperture effects on the derivation of O/H are discussed. Using our IFU data we obtain, for the first time, the IZw18 integrated spectrum.