Disk Formation in Hierarchical Hydrodynamical Simulations:A Way Out of the Angular Momentum Catastrophe

We report results on the formation of disk-like structures in twocosmological hydrodynamical simulations in a hierarchical clustering scenario,sharing the same initial conditions. In the first one, a simple and genericimplementation of star formation has allowed galaxy-like objects with stellarbulges and extended, populated disks to form. Gas in the disk comes from both,particles that survive mergers keeping in part their angular momentum content,and new gas supply by infall, once the merger process is over, with globalspecific angular momentum conservation. The stellar bulge forms from gas thathas lost most of its angular momentum. In the second simulation, no starformation has been included. In this case, objects consist of an overpopulatedcentral gas concentration, and an extended, underpopulated disk. The centralconcentration forms from particles that suffer an important angular momentumloss in violent events, and it often contains more than 70% of the object'sbaryonic mass. The external disk forms by late infall of gas, that roughlyconserves its specific angular momentum. The difference between these twosimulations is likely to be due to the stabilizing character of the stellarbulge-like cores that form in the first simulation, which diminishes the inflowof gas triggered by mergers and interactions.Comment: 11 pages, 2 figures. Accepted by The Astrophysical Journal Letter