  The effects of merging histories of proto-objects on the angular momentum
distributions of the present-time dark matter haloes are analysed. An
analytical approach to the analysis of the angular momentum distributions
assumes that the haloes are initially homogeneous ellipsoids and that the
growth of the angular momentum of the haloes halts at their maximum expansion
time. However, the maximum expansion time cannot be determined uniquely,
because in the hierarchical clustering scenario each progenitor, or subunit, of
the halo has its own maximum expansion time. Therefore the merging history of
the halo may be important in estimating its angular momentum. Using the merger
tree model by Rodrigues & Thomas, which takes into account the spatial
correlations of the density fluctuations, we have investigated the effects of
the merging histories on the angular momentum distributions of dark matter
haloes. It was found that the merger effects, that is, the effects of the
inhomogeneity of the maximum expansion times of the progenitors which finally
merge together into a halo, do not strongly affect the final angular momentum
distributions, so that the homogeneous ellipsoid approximation happens to be
good for the estimation of the angular momentum distribution of dark matter
haloes. This is because the effect of the different directions of the angular
momenta of the progenitors cancels out the effect of the inhomogeneity of the
maximum expansion times of the progenitors.
