The results of an investigation into the star formation history of elliptical galaxies, and the
subsequent implications for the still controversial issue of their formation and evolution are
presented. New, high signal-to-noise data and new, non-solar metallicity models motivate
the re-investigation of elliptical galaxy formation with synthetic stellar population models,
which has been difficult in the past because of uncertainties in the model spectra and the
effects of age-metallicity degeneracy.
Three different groups of elliptical galaxies, covering a range of redshift and nuclear activity
are investigated. The rest-frame optical spectra of a population of 24 low-redshift (z ≃ 0.2)
AGN host galaxies, together with the high-quality rest-frame ultraviolet spectra of two
high-redshift (z ≃ 1.5) mJy radio galaxies and ultraviolet-to-optical spectra of two lowredshift (z < 0.1) inactive galaxies are compared with a range of simple, near-instantaneous
starburst stellar population model spectra from various authors. With the benefit of nonsolar metallicity models, the attempt is made to reliably determine the ages and metallicities
of the stellar populations of the observed galaxies via continuum fitting.
A simultaneous test of the ability of these models to accurately reproduce the spectra of
real stellar populations is also presented. This is carried out both by testing the models’
ability to recover the correct ages and metallicities of two well-studied F stars and the Sun,
in the regimes where these stars dominate the integrated model flux, and by investigating
the quality of the continuum fits to the observed galaxy spectra.
With high-quality data, and reliable model spectra, it is possible to lift age-metallicity degeneracy, and robustly constrain the ages and metallicities of the galaxies studied. Models
with stellar populations of more than one age and / or metallicity have been constructed,
and this has allowed composite galaxy populations to be disentangled.
The results are consistent with the existence of two classes of elliptical galaxies, one formed at
high redshift, with predominantly passive evolution, and the other formed at lower redshift,
from galaxy-galaxy merging, with associated star formation. The spectroscopic determination of the stellar content of the galaxies studied has enabled their epochs of star formation
to be determined, and hence their formation routes.
The constraints imposed by the reliable identification of old stellar populations at known
redshift favour a A-dominated cosmological model, and strongly reject an Einstein-de Sitter