MINOR MERGERS AND THE SIZE EVOLUTION OF ELLIPTICAL GALAXIES

Using a high resolution hydrodynamical cosmological simulation of the formation of a massive spheroidal galaxy we show that elliptical galaxies can be very compact and massive at high redshift in agreement with recent observations. Accretion of stripped in-falling stellar material increases the size of the system with time and the central concentration is reduced by dynamical friction of the surviving stellar cores. In a specific case of a spheroidal galaxy with a final stellar mass of 1.5×10 11 M ⊙ we find that the effective radius re increases from 0.7±0.2 kpc at z = 3 to re = 2.4 ± 0.4 kpc at z = 0 with a concomitant decrease in the effective density of an order of magnitude and a decrease of the central…