FUSE observations of the H I interstellar gas of I Zw 18
Abstract
We present the analysis of FUSE observations of the metal-deficient dwarf galaxy I Zw 18 . We measured column densities of H I, N I, O I, Ar I, Si II, and Fe II. The O I/H I ratio (\log(O I/H I)=-4.7+0.8-0.6) is consistent with the O/H ratio observed in the H II regions (all uncertainties are 2-σ). If the oxygen is depleted in the H I region compared to the H II 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 H I regions of other blue compact dwarf galaxies. With \log(N I/O I)=-2.4+0.6-0.8, the measured N I/O I ratio is lower than expected for primary nitrogen. The determination of the N II column density is needed to discriminate between a large ionization of N I or a possible nitrogen deficiency. The neutral argon is also apparently underabundant, indicating that ionization into Ar II is likely important. The column densities of the other α-chain elements Si II and Ar I favor the lower edge of the permitted range of O I column density, \log (Ncm-2(O I))∼ 16.3.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- January 2004
- DOI:
- 10.1051/0004-6361:20031518
- arXiv:
- arXiv:astro-ph/0309766
- Bibcode:
- 2004A&A...413..131L
- Keywords:
-
- line: profiles;
- galaxies: abundances;
- galaxies: dwarf;
- galaxies: ISM;
- galaxies: individual: I Zw 18;
- ultraviolet: galaxies;
- Astrophysics
- E-Print:
- Accepted for publication in A&