A Physical Model for the Joint Evolution of Qsos and Spheroids

We present a detailed, physically grounded, model for the early coevolution of spheroidal galaxies and of active nuclei at their centers. The model is based on very simple recipes, that can be easily implemented. The main components and the transfer processes accounted for are depicted in Fig. 1, while we defer to Granato et al. (2004) for a full description. In summary, we start from the diffuse gas within the dark matter halo falling down into the star forming regions at a rate ruled by the dynamic and the cooling times. Part of this gas condenses into stars, at a rate again controlled by the local dynamic and cooling times. But the gas also feels the feedback from supernovae and from active nuclei, heating it and possibly expelling it from the potential well. Also the radiation drag on the cold gas decreases its angular momentum, causing an inflow into a reservoir around the central black hole. Viscous drag then causes the gas to flow from the reservoir into the black hole, increasing its mass and powering the nuclear activity. Among the most novel point of our work with respect to other semi-analytic approaches, we point out the treatment of the evolution of QSO activity in the forming spheroids, and of the resulting effects on galaxy evolution.