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Centro de Astrofísica da Universidade do Porto

Spatially resolved integral field spectroscopy of the ionized gas in IZw18

C. Kehrig, J. M. Vílchez, E. Pérez-Montero, J. Iglesias-Páramo, J. D. Hernández-Fernández, S. Duarte Puertas, J. Brinchmann, F. Durret, D. Kunth

Abstract
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 (̃1.4 × 1.4 kpc2) 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 R23 and the ionization parameter (as traced by [O III]/[O II]) across IZw18. Over ̃0.30 kpc2, using the [O III] λ4363 line, we compute Te[O III] values (̃15 000-25 000 K), and oxygen abundances are derived from the direct determinations of Te[O III]. More than 70 per cent of the higher-Te[O III] (≳22 000 K) spaxels are He IIλ4686-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.

Keywords
H II regions, galaxies: dwarf, galaxies: individual: IZw18, galaxies: ISM, galaxies: starburst

Monthly Notices of the Royal Astronomical Society
Volume 459, Page 2992
April 2016

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