Spatially resolved integral field spectroscopy of the ionized gas in IZw18

We present a detailed 2D study of the ionized ionized interstellar medium (ISM) of IZw18 using new Potsdam Multi-Aperture Spectrophotometer-integral field unit (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 (similar to 1.4 x 1.4 kpc(2)) 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 north-west knot and thereabouts. We detect a Wolf-Rayet feature near the north-west 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-23 and the ionization parameter (as traced by [O III]/[O II]) across IZw18. Over similar to 0.30 kpc(2), using the [O III] lambda 4363 line, we compute T-e[O III] values (similar to 15 000-25 000 K), and oxygen abundances are derived from the direct determinations of T-e[O III]. More than 70 per cent of the higher-T-e[O III] (greater than or similar to 22 000 K) spaxels are He II lambda 4686-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.