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A Universal Angular Momentum Profile for Dark Matter Halos

2017; IOP Publishing; Volume: 844; Issue: 1 Linguagem: Inglês

10.3847/1538-4357/aa79fb

1538-4357

Shihong Liao, Chen Jianxiong, M. C. Chu,

Remote Sensing in Agriculture

Abstract The angular momentum distribution in dark matter halos and galaxies is a key ingredient in understanding their formation. Specifically, the internal distribution of angular momenta is closely related to the formation of disk galaxies. In this article, we use halos identified from a high-resolution simulation, the Bolshoi simulation, to study the spatial distribution of specific angular momenta, <?CDATA $j(r,\theta )$?> . We show that by stacking halos with similar masses to increase the signal-to-noise ratio, the profile can be fitted as a simple function, <?CDATA $j{(r,\theta )={j}_{s}{\sin }^{2}{(\theta /{\theta }_{s})(r/{r}_{s})}^{2}/(1+r/{r}_{s})}^{4}$?> , with three free parameters, <?CDATA ${j}_{s},{r}_{s}$?> , and <?CDATA ${\theta }_{s}$?> . Specifically, j s correlates with the halo mass M vir as <?CDATA ${j}_{s}\propto {M}_{\mathrm{vir}}^{2/3}$?> , r s has a weak dependence on the halo mass as <?CDATA ${r}_{s}\propto {M}_{\mathrm{vir}}^{0.040}$?> , and <?CDATA ${\theta }_{s}$?> is independent of M vir . This profile agrees with that from a rigid shell model, though its origin is unclear. Our universal specific angular momentum profile <?CDATA $j(r,\theta )$?> is useful in modeling the angular momenta of halos. Furthermore, by using an empirical stellar mass–halo mass relation, we can infer the average angular momentum distribution of a dark matter halo. The specific angular momentum–stellar mass relation within a halo computed from our profile is shown to share a similar shape as that from the observed disk galaxies.