On the formation of spiral galaxies
The formation of spiral galaxies is a major challenge for cosmological models. These galaxy grow through mergers and accretion of cold gas along cosmic filaments, but the interplay between these mechanisms is still to be understood. For instance, the origin of the different components of the
Milky-Way (its bulge, thick and thin disks and stellar halo) is poorly constrained, and no cosmological simulation so far has been able to explain the existence of galaxies with very low bulge-to-disk mass ratios. I will present some recent results on the formation of thick disks of nearby galaxies, arguing that they most probably were formed at high redshift because of violent disk instabilities following rapid accretion of cold gas. I will also show that the continuous return of gas by evolved stellar
populations (through stellar winds and planetary nabulae) could play a major part in the formation of galaxies with a small bulge and an extended disk.