Astron. Astrophys. 343, 720-732 (1999)

Astron. Astrophys. 343, 720-732 (1999)

The metallicity distribution and the G-dwarf problem in elliptical galaxies

L. Angeletti and P. Giannone

Istituto Astronomico, Università `La Sapienza', Via Lancisi 29, I-00161 Roma, Italy

Received 12 May 1998 / Accepted 22 November 1998

Abstract

We investigate distributions of the stellar metallicity Z which can solve the local (within the effective radius) and/or the global G-dwarf problem in elliptical galaxies. We represent an elliptical galaxy with the spherical and isotropic model by Hernquist (1990) and relate the Z dispersion to the stellar binding energy [FORMULA] . Such a Z- relation may be a single-valued function Z(), or an -dependent Z spectrum for each value of in its proper range. In this preliminary paper we only consider a stellar component of one age, thus disregarding a superposition of several independent Z- relations. Moreover, we adopt an exploratory approach with the aid of a few simple Z- [FORMULA] relations, and take into account the observed colours and metallicity radial gradients together with the and correlations. We find that some of the adopted Z- relations fit reasonably well the observed correlations and, at the same time, can solve the local and/or the global G-dwarf problem. In particular, the `Simple Model' can remove the local G-dwarf problem but not the global one, whereas the `Best Accretion Model' by Lynden-Bell (1975) can avoid both problems. Furthermore, our results suggest a viable approach to the formulation of a flexible Z- [FORMULA] relation, either as a single-valued Z() or an -dependent Z spectrum, that can solve the G-dwarf problem and agree with all the major observational evidences. We confirm that the mean metallicities, as inferred from the Single Stellar Populations and observed colours or spectral indices (e.g. [FORMULA] ), may be underestimated by up to a factor of two, owing to the stellar metallicity spread in real ellipticals.