A universal angular momentum profile for dark matter haloes [GA]


The angular momentum distribution in dark matter haloes and galaxies is a key ingredient in understanding their formation. Especially, the internal distribution of angular momenta is closely related to the formation of disk galaxies. In this article, we use haloes identified from a high-resolution simulation, the Bolshoi simulation, to study the spatial distribution of specific angular momenta, $j(r,\theta)$. We show that by stacking haloes with similar masses to increase the signal-to-noise ratio, the profile can be fitted as a simple function, $j(r,\theta)=j_s \sin^2(\theta/\theta_s) (r/r_s)^2/(1+r/r_s)^4 $, with three free parameters, $j_s, r_s$, and $\theta_s$. Specifically, $j_s$ correlates with the halo mass $M_\mathrm{vir}$ as $j_s\propto M_\mathrm{vir}^{2/3}$, $r_s$ has a weak dependence on the halo mass as $r_s \propto M_\mathrm{vir}^{0.040}$, and $\theta_s$ is independent of $M_\mathrm{vir}$. This profile agrees with that from a rigid shell model, though its origin is unclear. Our universal specific angular momentum profile $j(r,\theta)$ is useful in modelling haloes’ angular momenta. Furthermore, by using an empirical stellar mass – halo mass relation, we can infer the averaged angular momentum distribution of a dark matter halo. This is supported by the agreement between the maximum specific angular momentum predicted by our profile and those from observational data of disk galaxies.

Read this paper on arXiv…

S. Liao, J. Chen and M. Chu
Fri, 2 Dec 16

Comments: 10 pages, 7 figures, submitted to ApJ