Formation and Evolution of Early-Type Galaxies. III Star formation
  history as a function of mass and over-density
  We investigate the influence of the initial proto-galaxies over-densities and
masses on their evolution, to understand whether the internal properties of the
proto-galactic haloes are sufficient to account for the varied properties of
the galactic populations. By means of fully hydrodynamical N-body simulations
performed with the code EvoL we produce twelve self-similar models of
early-type galaxies of different initial masses and over-densities, following
their evolution from z \geq 20 down to z \leq 1. The simulations include
radiative cooling, star formation, stellar energy feedback, a reionizing
photoheating background, and chemical enrichment of the ISM. We find a strong
correlation between the initial properties of the proto-haloes and their star
formation histories. Massive (10^13M\odot) haloes experience a single, intense
burst of star formation (with rates \geq 10^3M\odot/yr) at early epochs,
consistently with observations, with a less pronounced dependence on the
initial over-density; intermediate mass (10^11M\odot) haloes histories strongly
depend on their initial over-density, whereas small (10^9M\odot) haloes always
have fragmented histories, resulting in multiple stellar populations, due to
the "galactic breathing" phenomenon. The galaxy models have morphological,
structural and photometric properties comparable to real galaxies, often
closely matching the observed data; even though some disagreement is still
there, likely a consequence of some numerical choices. We conclude that
internal properties are essentially sufficient to explain many of the observed
features of early type galaxies, particularly the complicated and different
star formation histories shown by haloes of very different mass. In this
picture, nature seems to play the dominant role, whereas nurture has a
secondary importance.
