Abundance differences between the neutral and the ionized gas of the dwarf galaxy IZw 36

¹ Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, 75014 Paris, France
² LERMA - Bâtiment A, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France

Corresponding author: V. Lebouteiller, leboutei@iap.fr

Received: 2 June 2003
Accepted: 17 October 2003

Abstract

We present a FUSE spectroscopic study of the nearby gas–rich, metal–deficient blue compact dwarf (BCD) galaxy IZw 36. Atomic hydrogen and many metal lines are observed in absorption against the stellar continuum of young, massive stars embedded in the ionized region. Profile fitting of absorption lines allowed us to determine abundances and investigate the chemical composition of the neutral gas. This study presents strong evidence that nitrogen is 16 times less abundant in the neutral gas than in the ionized gas (all uncertainties are 2σ). Similarly, the oxygen abundance estimated using phosphorus as a tracer is lower in the neutral gas by a factor of 8. We also find that argon is underabundant by a factor of 32 and that log (Ar i/O i) < -3.0 which is inconsistent with the Ar/O ratio -2.1 ± 0.1 (Lodders [CITE]), implying that argon is likely ionized into Ar ii in the neutral medium.