CfA OIR Division Lunch Talks
Wednesday, May 7, 2008, 11:00 am, Pratt Conference Room
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Modelling Hierarchical Galaxy Formation with GalICS

Dr. Bruno Guiderdoni (Observatory of Lyon)

In the current paradigm, galaxies form within Cold Dark Matter structures through dissipative collapse of the baryonic component in the potential wells of the dark matter halo hierarchy, and eventually merge to form bigger objects. I shall discuss an implementation of this scenario though the so-called "hybrid approach", in which dark matter collapse is described by a numerical simulation of a dark matter cosmological volume, and the baryonic processes involved in galaxy formation are modelled in a semi-analytic post-proccesing of the dark matter outputs. The GalICS model (for "Galaxies in Cosmological Simulations") result from a five-year effort that started at the Paris Institute of Astrophysics (Hatton et al. 2003, MNRAS 343, 75), and continued at the Observatory of Lyon. I shall describe the basic features of the model, and show how it reproduces quite nicely some of the basic statistical properties of galaxies in the local universe, as well as their evolution back in time (e.g., Lyman Break Galaxies). The model can be used to generate mock images and catalogues that are useful for preparing observations. As an example of the GalICS approach, I will use this model to show that some ingredients are missing if we are to explain the bimodal distribution of the colours of galaxies, as they appear in the SDSS data. I will explain how new physical ingredients added in the code (i.e., a re-examination of the cooling processes) produce results which are much more in agreement with the data (see e.g., Cattaneo et al. 2008, MNRAS, in press).