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Astron. Astrophys. 325, 1025-1030 (1997)

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4. Conclusions

This study confirms that spectral indices or equivalent widhts of [FORMULA] and of the other Balmer lines depend on metallicity in SSPs and galaxies and therefore cannot be used as pure age indicator. On the other side, this metallicity dependence can account for variations of the equivalent widths up to certain values (typically 1.5 Å for H [FORMULA] and H [FORMULA] for old SSPs) and above such values age differences need to be taken into account.

Results for galaxy models are shown in Table 2. In spirals the absorption line is partially filled in by the gaseous emission; the separate contributions are given as well. The very metal poor populations are unable to give rise to strong [FORMULA] in the integrated spectrum of galaxies. This confirms that an [FORMULA] as high as those observed in distant cluster galaxies is the signature of an enhanced star formation episode in the last 2 Gyr and cannot be due to metallicity.

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998