An Analytical Approach to the Spin-Distribution of Dark Halos

Abstract

We derive the distribution of the dimensionless specific angular momentum of dark matter halos, $P(j)$, in the framework of the standard tidal torque theory, and explain the characteristic shape of $P(j)$ commonly observed in N-body simulations. A scalar quantity (shear scalar), $r$, is introduced for measuring the effective strength of the tidal torque force acting upon the halo from the surrounding matter. It is found that the ubiquitous and broad shape of $P(j)$ can mostly be attributed to the unique property of the shear scalar $r$, and also that $P(j)$ is insensitve to the underlying collapse dynamics. Our result demonstrates that although the shape of $P(j)$ is ubiquitous and close to log-normal, the distribution is not exactly log-normal but decays exponentially at the high angular momentum end, and drops slowly as a power-law with an index 2 at the low angular momentum end.

14 pages including two figures, submitted to ApJ Lett

References in corpus (7)

• An excursion set model of hierarchical clustering: Ellipsoidal collapse and the moving barrier
• The origin of angular momentum in dark matter halos
• Testing Tidal-Torque Theory: I. Spin Amplitude and Direction
• Testing Tidal-Torque Theory: II. Alignment of Inertia and Shear and the Characteristics of Proto-haloes
• Modeling Angular-Momentum History in Dark-Matter Halos
• The Angular Momentum Distribution within Halos in Different Dark Matter Models
• Bias and Conditional Mass Function of Dark Halos Based on the Nonspherical Collapse Model

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