SIMBAD references

We address the problem of the formation and evolution of elliptical galaxies (from dwarf to normal/giant systems). In particular, by means of N -body-tree-SPH simulations, incorporating cooling, star formation, energy feedback and chemical evolution, we intend to explore whether the formation of elliptical galaxies from the monolithic collapse of baryons inside non-rotating, virialized haloes of dark matter leads to results compatible with the main body of observational data on these systems. We show that this scenario can indeed reproduce the basic structural properties of observed elliptical galaxies of different mass.

We study the star formation history and the chemical enrichment of the models, showing that the duration, strength and shape of the star formation rate as a function of time depend strongly on the galaxy mass and the initial density. More precisely, massive elliptical galaxies, independent of their initial density, show a single burst of star formation, whereas the low-mass ones have a varied star formation history. It is early and monolithic in the high initial density systems, and irregular and intermittent in the low-density ones.

The occurrence of galactic winds is also analysed, and we conclude that in general all galaxies are able to eject part of their gas content into the intergalactic medium. However, the percentage of the ejected material increases with decreasing galaxy mass.

Our models are used to interpret the fundamental plane (mass-to-light ratio versus mass relationship), the mass-to-light ratio versus central velocity dispersion, the colour-magnitude relation and the mass-radius relationships of elliptical galaxies from dwarfs to giants. For each relationship in question the agreement between observations and theory is remarkable.

Based on this, we endeavour to speculate on a unified scheme for the formation of stellar aggregates going from globular clusters to normal/giant elliptical galaxies in which initial density, type of star formation (single initial episode or recurrent bursts of activity) and galactic winds are the key ingredients. Finally, we draw some conclusions concerning the long-standing question as to whether the hierarchical or the monolithic scheme for the formation of galaxies (ellipticals) ought to be preferred.