ABUNDANCES IN EXTRAGALACTIC H II REGIONS
Harriet L. Dinerstein
University of Texas at Austin
Abstract. Giant H II regions can be observed out to large
distances. They trace
recent star formation and, through the analysis of their chemical
composition, previous
star formation activity. Systematic effects such as metallicity
gradients across the disks of
spirals and the correlation of metallicity with total galaxy mass offer
important constraints
on galaxy evolution. The helium abundance in regions where the gas has
experienced
little stellar nuclear processing provides an important test of
cosmological theories. Some
of the current uncertainties in interpreting nebular spectra are likely
to be resolved by the
next generation of ground-based, airborne, and spaceborne telescopes.
For a postscript version of the article, click
here.
INTRODUCTION
H II Regions in the Context of the ISM
Environments and Systematics
Internal Structure
Ionizing Clusters
METHODS OF ABUNDANCE DETERMINATION
ABUNDANCE GRADIENTS IN GALACTIC DISKS
The Phenomenon
Trends with Galaxy Type
Elements other than Oxygen
Comparison with the Galactic Abundance Gradient
Comparison with Chemical Evolution Models
ABUNDANCES IN METAL-POOR DWARF GALAXIES
Nomenclature
The "I Zw 18 Problem" and the Mass-Metallicity
Relation
Dwarf Galaxies as Tests of the Simple Model
Dwarf Galaxies and the Extragalactic H II Region
Sequence
Elements other than Oxygen
HELIUM ABUNDANCES AND THE PRIMORDIAL COMPONENT
SOME OUTSTANDING ISSUES
FUTURE PROSPECTS
REFERENCES
