AAS Meeting #193 - Austin, Texas, January 1999
Session 70. Star Formation and the ISM in Galaxies
Display, Friday, January 8, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[70.08] Measuring Metal Abundances of Distant Galaxies from Integrated Emission-Line Spectra

R.C. Kennicutt (Steward Obs.), H.A. Kobulnicky (Lick Obs.), J.L. Pizagno (U. Arizona)

The advent of 8--10m class telescopes makes it possible to measure the chemical properties in the ionized gas in high-redshift galaxies using the same techniques that are applied to HII regions in nearby galaxies. We show that spatially integrated emission-line spectra can provide a reliable measurement of the mean metal abundances of distant star-forming galaxies.

Our analysis is based on a set of spatially-resolved spectra of metal-poor galaxies with measured electron temperatures (from [OIII]\lambda4363), published HII region spectra of metal-rich galaxies with internal abundance gradients, and integrated spectra for a subset of these objects. We used these data to synthesize integrated emission-line ratios for the galaxies and study the effects of spatial averaging on the excitation properties and metal abundances inferred from the global spectra. For massive metal-rich galaxies, well-established empirical calibrations based on strong-line ratios provide reliable measures (±0.2 dex) of the mean oxygen abundance for spectra with S/N \ge 8 in the diagnostic emission lines. More accurate abundances can be derived when [OIII]\lambda4363 is detected by applying small corrections (\Delta(O/H) = 0.1 dex) for systematic effects which are introduced by spatial variations in electron temperature and ionization parameter. We provide prescriptions for deriving oxygen abundances from the global emission-line spectra of high-redshift galaxies, and assess the main sources of systematic error in these applications.

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