We present a sample of nine high resolution cosmological simulations in the mass range of M _ { vir } = 7 \times 10 ^ { 11 } -4 \times 10 ^ { 12 } M _ { \odot } starting from \Lambda CDM initial conditions .
Our simulations include primordial radiative cooling , photoionization , star formation , supernova II feedback , but exclude supernova driven winds and AGN feedback .
The simulated galaxies assemble in two phases , with the initial growth dominated by compact ( r < r _ { eff } ) in situ star formation fueled by cold , low entropy gas streams resulting in a very similar mean assembly redshift of z _ { f,ins } \sim 2.5 for the in situ stellar component in all galaxies .
The late growth is dominated by accretion of old stars formed in subunits outside the main galaxy ( r > r _ { eff } ) resulting in an assembly redshift of z _ { f,acc } \sim 0.5 - 1.5 with much larger scatter .
We find a positive correlation between the fraction of accreted stars and the final mass of our galaxies .
We show that gravitational feedback strongly suppresses late star formation in massive galaxies contributing to the observed galaxy color bimodality .
The accretion of stellar material is also responsible for the observed size growth of early-type galaxies .
In addition , we find that the dark matter fractions within the stellar half-mass radii continuously increase towards lower redshift from about f _ { DM } \sim 0.05 at z \sim 3 to f _ { DM } \sim 0.1 - 0.3 at z = 0 .
Furthermore , the logarithmic slope of the total density profile is nearly isothermal at the present-day ( \gamma ^ { \prime } \sim 1.9 - 2.2 ) .
Finally , the input of gravitational heating lowers the central dark matter densities in the galaxies , with the effect being smaller compared to simulations without supernova feedback .