Effects of Angular Momentum on Halo Profiles

TL;DR

This study investigates how adding angular momentum to dark matter halos affects their density profiles, finding that moderate spins preserve the universal profile while high spins cause deviations and often lead to bar structures.

Contribution

It demonstrates that halo density profiles remain universal for moderate spins and explores the impact of high spins on halo structure and bar formation.

Findings

Halos with spin parameter λ ≤ 0.20 retain universal density profiles.

High spins (λ ≥ 0.20) cause noticeable deviations in halo profiles.

Strong bar structures are associated with high-spin halos and resemble radial orbit instability.

Abstract

The near universality of DM halo density profiles provided by N-body simulations has proven to be robust against changes in total mass density, power spectrum, and some forms of initial velocity dispersion. In this letter we study the effects of coherently spinning up an isolated DM-only progenitor on halo structure. Halos with spins within several standard deviations of the simulated mean ($\lambda \lesssim 0.20$) produce profiles with negligible deviations from the universal form. Only when the spin becomes quite large ($\lambda \gtrsim 0.20$) do departures become evident. The angular momentum distribution also exhibits a near universal form, which is also independent of halo spin up to $\lambda \lesssim 0.20$. A correlation between these epidemic profiles and the presence of a strong bar in the virialized halo is also observed. These bar structures bear resemblance to the radial orbit instability in the rotationless limit.