The ISO Galactic metallicity gradient revisited

Abstract

Two independent groups (Giveon et al. \cite{giveon}; Martín-Hernández et al. \cite{martin}) have recently investigated the Galactic metallicty gradient as probed by ISO observations of mid-infrared emission-lines from HII regions. We show that the different gradients inferred by the two groups are due to differing source selection and differing extinction corrections. We show that both data sets in fact provide consistent results if identical assumptions are made in the analysis. We present a consistent set of gradients in which we account for extinction and variation in electron temperature across the Galactic disk. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the UK) with the participation of ISAS and NASA.