Simulations of Galaxy Formation: Feedback and the early formation of compact spheroids by disc instabilities.
Any successful model of galaxy formation needs to explain the low rate of star formation in the small progenitors of today’s galaxies. This inefficiency is necessary for reproducing the low stellar-to-virial mass fractions. A possible driver of this low efficiency is the radiation pressure exerted by ionizing photons from massive stars. The effect of radiation pressure in cosmological, zoom-in galaxy formation simulations is modelled as a non-thermal pressure that acts only in dense and optically thick star-forming regions. The main effect of radiation pressure is to regulate and limit the high values of gas density and the amount of gas available for star formation. By using these simulations, I will address the early formation of compact spheroids by violent disc instabilities (VDI). Due to the inefficiency of star formation, this process is gas rich, so the dissipation naturally leads to compact spheroids. These VDI-driven spheroids, much like merger-driven spheroids, have steep surface density profiles, consistent with a classical, de-Vaucouleurs profile at all times.