A density-gradient model for the H II galaxy I Zw 18

Journal Article · Mon Oct 01 04:00:00 EDT 1990 · Astrophysical Journal; (USA)

DOI:https://doi.org/10.1086/169246· OSTI ID:6231283

Campbell, A ^[1]

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1. Carnegie Institution of Washington, Washington, DC (USA)

Most of the lowest-metallicity galactic systems known have emission-line ratios that are not well-fitted by a simple H II region model. These objects are similar to the low-abundance H II galaxy I Zw 18 in that the observed F(3727 A)/F(H-beta) does not agree with the predictions of models that fit F(4363 A)/F(H-beta), and F(4363)/F(4959, 5007), casting doubt on the oxygen abundance estimated from the line ratios. Here, the observed emission-line ratios of I Zw 18 are compared with those of model nebulae incorporating a density gradient. An attempt is made to develop a self-consistent model capable of explaining all existing observations of I Zw 18 and to investigate the possibility that the true oxygen abundance of this object is higher than the very low value obtained from the estimated electron temperature of O(2+). 25 refs.

• OSTI ID: 6231283
• Journal Information: Astrophysical Journal; (USA), Journal Name: Astrophysical Journal; (USA) Vol. 362; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BALMER LINES
CHARGED PARTICLES
CHEMICAL COMPOSITION
COMPARATIVE EVALUATIONS
COSMIC RADIO SOURCES
ELECTRON DENSITY
EMISSION SPECTRA
GALAXIES
H2 REGIONS
IONS
MATHEMATICAL MODELS
OXYGEN IONS
SPECTRA