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We perform a set of non-radiative hydrodynamical simulations of mergingspherical halos in order to understand the angular momentum (AM) properties ofthe galactic halos seen in cosmological simulations. The universal shape of AMdistributions seen in simulations is found to be generically produced as aresult of mergers. The universal shape is such that it has an excess of low AMmaterial and hence cannot explain the exponential structure of disk galaxies. Aresolution to this is suggested by the spatial distribution of low AM materialwhich is found to be in the centre and a conical region close to the axis ofrotation. A mechanism that preferentially discards the material in the centreand prevents the material along the poles from falling onto the disc isproposed as a solution. We implement a simple geometric criteria for selectiveremoval of low AM material and show that in order for 90% of halos to hostexponential discs one has to reject at least 40% of material. Next, we explorethe physical mechanisms responsible for distributing the AM within the haloduring a merger. For dark matter there is an inside-out transfer of AM, whereasfor gas there is an outside-in transfer, which is due to differences betweencollisionless and gas dynamics. We also explain the apparent high spin of darkmatter halos undergoing mergers and show that a criteria stricter than what iscurrently used, would be required to detect such unrelaxed halos. Finally, wedemonstrate that the misalignment of AM between gas and dark matter only occurswhen the intrinsic spins of the merging halos are not aligned with the orbitalAM of the system. The self-misalignment (orientation of AM when measured inradial shells not being constant), which could be the cause of warps andanomalous rotation in disks galaxies, also occurs under similar conditions.

On the origin of the angular momentum properties of gas and dark matter in galactic halos and its implications