Jounghun Lee, Gerard Lemson
We utilize the Millennium-II simulation databases to study the spin bias of dark subhalos in the Local Group-like environments. Selecting the group-size halos with total mass comparable to that of the Local Group (LG) from the friends-of-friends halo catalog and locating their subhalos from the substructure catalog, we determine the most massive (main) and second to the most massive (submain) ones among the subhalos hosted by each selected halo. When the dimensionless spin parameter ($\lambda$) of each subhalo is derived from its specific angular momentum and circular velocity maximum, a clear signal of strong correlation is detected between the spin parameters of the subhalos and the main-to-submain mass ratios of their host halos at $z=0$: The higher main-to-submain mass ratio a host halo has, the higher mean spin parameter its subhalos have. It is also found that the correlation becomes weaker at higher redshifts, diminishing to negligible level at $z=1$. Our interpretation of this result is that the strong anisotropic stress in the host halo with high main-to- submain mass ratio should be responsible for the bias of its subhalos toward the high spin parameters and that the spin bias becomes stronger at lower redshits when dark energy plays a role of enhancing the anisotropic stress. A cosmological implication of our result is also discussed.
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http://arxiv.org/abs/1303.0674
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