Chemical evolution of local galaxies in a hierarchical model
  We investigate the chemical properties of local galaxies within a
cosmological framework in the hierarchical picture of galaxy formation. To this
aim, we use a hierarchical semi-analytic model which includes the contribution
from (i) low and intermediate mass stars, (ii) type Ia Supernovae (SNe) and
(iii) massive stars. - Abridged - We compare our predictions with available
observations in the Milky Way (MW), in local dwarf galaxies and in local
ellipticals. For Milky-Way-like galaxies, we can successfully reproduce the
[O-Fe] vs [Fe/H] relation observed in disc stars and the stellar metallicity
distribution (SMD). For dwarf galaxies, the stellar metallicity vs mass
relation is reproduced by assuming that a substantial fraction of the heavy
elements is lost through metal-enhanced outflows and a type Ia SN realization
probability lower than the one of MW-like galaxies. - Abridged - In
ellipticals, the observations indicate higher [alpha/Fe] values in larger
galaxies. - Abridged - Our results computed with a standard Salpeter initial
mass function (IMF) indicate a flat [alpha/Fe]-sigma relation. However, we
suggest a possible solution to this problem and show how, by assuming a star
formation-dependent IMF with a slope x=1.35 in systems with star formation
rates < 100 M_sun/yr and slightly flatter (i.e. with x=1) in object with
stronger star formation, the observed correlation between [alpha/Fe] and sigma
can be accounted for on a large velocity dispersion range. Fundamental roles
are played also by interaction-triggered starbursts and AGN.
