The cosmological dependence of galactic specific angular momenta

Hydrodynamical simulations of galaxy formation in spatially flat cold dark matter (CDM) cosmologies with and without a cosmological constant (Lambda) are described. A simple star formation algorithm is employed and radiative cooling is allowed only after redshift z = 1 so that enough hot gas is avai lable to form large, rapidly rotating stellar discs if angular momentum is approximately conserved during collapse. The specific angular momenta of th e final galaxies are found to be sensitive to the assumed background cosmol ogy. This dependence arises from the different angular momenta contained in the haloes at the epoch when the gas begins to collapse and the inhomogene ity of the subsequent halo evolution. In the Lambda-dominated cosmology, th e ratio of stellar specific angular momentum to that of the dark matter hal o (measured at the virial radius) has a median value of similar to 0.24 at z = 0. The corresponding quantity for the Lambda = 0 cosmology is over thre e times lower. It is concluded that the observed frequency and angular mome nta of disc galaxies pose significant problems for spatially flat CDM model s with Lambda = 0 but may be consistent with a Lambda-dominated CDM univers e.