Galaxy formation - the role of tidal torques and dissipational infall

Galaxies are assumed to form by the gravitational collapse of density peaks in an Omega = 1 universe dominated by cold dark matter. Protogalaxies are torqued up by tidal interactions with the surrounding density field. The rms specific angular momentum acquired through tidal torques has the form h proportional to M exp 4/3 around a density peak. The dimensionless angular momentum parameter has the value 0.09 for a 3 sigma density peak on the scale 10 to the 9th solar masses and is weakly anticorrelated with initial peak height. The baryonic portion of the collapsed structures are able to cool efficiently through bremsstrahlung. If the dissipating baryons form a rotationally supported disk, adiabatically compressing the surrounding dark matter, then the resulting structures have flat rotation curves. A 3 sigma peak on a mass scale of 10 to the 9th solar masses has a rotation velocity of about 220 km/s after dissipation; the baryonic component is dynamically dominant at radii less than about 4 kpc. 27 references