Angular Momentum Profiles of Warm Dark Matter Halos

We compare the specific angular momentum profiles of virialized dark halos incold dark matter (CDM) and warm dark matter (WDM) models using high-resolutiondissipationless simulations. The simulations were initialized using the sameset of modes, except on small scales, where the power was suppressed in WDMbelow the filtering length. Remarkably, WDM as well as CDM halos arewell-described by the two-parameter angular momentum profile of Bullock et al.(2001), even though the halo masses are below the filtering scale of the WDM.Although the best-fit shape parameters change quantitatively for individualhalos in the two simulations, we find no systematic variation in profile shapesas a function of the dark matter type. The scatter in shape parameters issignificantly smaller for the WDM halos, suggesting that substructure and/ormerging history plays a role producing scatter about the mean angular momentumdistribution, but that the average angular momentum profiles of halos originatefrom larger-scale phenomena or a mechanism associated with the virializationprocess. The known mismatch between the angular momentum distributions of darkhalos and disk galaxies is therefore present in WDM as well as CDM models. OurWDM halos tend to have a less coherent (more misaligned) angular momentumstructure and smaller spin parameters than do their CDM counterparts, althoughwe caution that this result is based on a small number of halos.Comment: 5 pages, 1 figure, Submitted to ApJ