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Astron. Astrophys. 335, 855-866 (1998)

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On the trend of [Mg/Fe] among giant elliptical galaxies

Francesca Matteucci 1, 2, Raffaella Ponzone 1, 2 and Brad K. Gibson 3

1 Dipartimento di Astronomia, Università di Trieste, Via G.B. Tiepolo, 11, I-34131 Trieste, Italy
2 SISSA/ISAS, Via Beirut 2-4, I-34014 Trieste, Italy
3 Mt. Stromlo and Siding Spring Observatories, Australian National University, Weston Creek, ACT 2611, Australia

Received 17 February 1998 / Accepted 16 March 1998


We revisit the problem of the flat slope of the [FORMULA] versus [FORMULA] relationship found for nuclei of elliptical galaxies (Faber et al. 1992; Worthey et al. 1992; Carollo et al. 1993; Davies et al. 1993), indicating that the Mg/Fe ratio should increase with galactic luminosity and mass. We transform the abundance of Fe, as predicted by classic wind models and alternative models for the chemical evolution of elliptical galaxies, into the metallicity indices [FORMULA] and [FORMULA], by means of the more recent index calibrations and show that none of the current models for the chemical evolution of elliptical galaxies is able to reproduce exactly the observed slope of the [FORMULA] versus [FORMULA] relation, although the existing spread in the data makes this comparison quite difficult. In other words, we can not clearly discriminate between models predicting a decrease (classic wind model) or an increase of such a ratio with galactic mass. The reason for this resides in the fact that the available observations show a large spread due mostly to the errors in the derivation of the [FORMULA] index. In our opinion this fact prevents us from drawing any firm conclusion on the behaviour of Mg and Fe in these galaxies. Moreover, as already shown by other authors, one should be careful in deriving trends in the real abundances just from the metallicity indices, since these latter depend also on other physical parameters than the metallicity. This is an important point since abundance ratios have been proven to represent strong constraints for galaxy formation mechanisms.

Key words: nuclear reactions, nucleosynthesis, abundances – galaxies: elliptical and lenticular, cD – galaxies: evolution – galaxies: abundances

Send offprint requests to: F. Matteucci

© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998