| Description: | In galaxy formation scenarios, slow dynamical processes, where the galaxies remain in quasi-equilibrium, while continuously accreting matter from cosmic filaments, compete with more violent evolution, triggered by galaxy interactions and mergers. Galaxy disks develop non-axisymmetric waves, such as bars and spirals, to transfer efficiently the angular momentum outwards, and concentrate the mass. Perpendicular bar resonances form pseudo-bulges, which are frequently observed in particular in late-type galaxies. The relative importance of the two formation/evolution scenarios to assemble mass will be discussed. Secular evolution may alleviate the problem of too massive bulge formation in the standard LCDM theory. The observed bar frequency can also quantify the amount of slow gas accretion all along a galaxy life-time. Typically a galaxy would double its mass in about 10 Gyr. Cosmological simulations confirm the importance of accretion.
Image Caption:Montage of an HST image of NGC 1300, a strongly barred galaxy, with numerical simulation snapshots of the evolution of barred spiral galaxies. |
