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5. CONCLUSIONS

In the standard model, classical bulges are thought to be formed essentially in galaxy mergers, which are very frequent in the hierarchical scenario of galaxy formation. In addition, a small classical bulge is also formed in the first Gyr of the galaxy lifes, during the clumpy phase, where their disk is gas dominated. Later on, pseudo-bulges formed out of bar resonances are adding their contribution to the classical bulges.

In the frame of MOND, bulges are hardly formed in early times, in the clumpy phase of galaxy formation, since the dynamical friction without dark matter halos is not efficient enough to drive clumps towards the center, before they are destroyed or reduced by stellar feedback and shear forces. Classical bulges can form later, through hierarchical merging, with a frequency which is smaller than what occurs in the analogous Newtonian systems with dark matter. They however form with comparable frequency through secular evolution, by vertical resonances with bars. It is therefore expected that the contribution of pseudo-bulges with respect to classical bulges is higher in MOND. Globally, bulges are expected less frequent and less massive, which might be more compatible with observations of local galaxies (Weinzirl et al. 2009, Kormendy et al. 2010). These tendencies have to be confirmed with more simulations. A complete cosmological context is however not yet possible, given the uncertainties of the modified gravity models in the early universe.

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