2004A&A...413..131L

We present the analysis of FUSE observations of the metal-deficient dwarf galaxy IZw18. We measured column densities of HI, NI, OI, ArI, SIII, and FeII. The OI/HI ratio (log(OI/HI)=-4.7^+0.8_–0.6) is consistent with the O/H ratio observed in the HII regions (all uncertainties are 2-σ). If the oxygen is depleted in the HI region compared to the HII regions, the depletion is at most 0.5 dex. This is also consistent with the log(O/H) ratios ~-5 measured with FUSE in the HI regions of other blue compact dwarf galaxies. With log(NI/OI)=-2.4^+0.6_–0.8, the measured NI/OI ratio is lower than expected for primary nitrogen. The determination of the NII column density is needed to discriminate between a large ionization of NI or a possible nitrogen deficiency. The neutral argon is also apparently underabundant, indicating that ionization into ArII is likely important. The column densities of the other α-chain elements SIII and ArI favor the lower edge of the permitted range of OI column density, log(N_cm-2^_(OI))∼16.3.