Merging Histories on Angular Momentum Distribution of Dark Matter Haloes

E ects of merging histories of protoobjects on angular momentum distribution of present dark matter haloes are analysed. In a analysis of the angular momentum distributions by analytical methods (e.g., Heavens & Peacock 1989, Catelan & Theuns 1996), they have assumed that initially haloes are homogeneous ellipsoids and that the growth of the angular momentum halts at the maximum expansion time of the haloes. However, more realistically, the maximum expansion time of a halo cannot be determined uniquely because each protoobject of the halo has each maximum expansion time in the hierarchical clustering scenario. So merging histories of haloes may a ect the angular momentum of the haloes. Using the merger tree model proposed by Rodrigues & Thomas (1996), which includes the information of spatial correlations of density uctuations owing to a grid-based realisation of density uctuations, we investigate e ects of the merging histories on the angular momentum distribution of dark matter haloes. We nd that the merger e ect does not strongly a ect the nal angular momentum distribution. Moreover, we investigate contribution of the orbital angular momentum to the total angular momentum when two or more pre-existing haloes merge each other. We nd that the contribution is important especially in the case that merger occurs many times.