On the spin parameter of dark-matter haloes

• Verfasst von: Steinmetz, Matthias [VerfasserIn]
• Verfasst von: Bartelmann, Matthias [VerfasserIn]
• Titel: On the spin parameter of dark-matter haloes
• Verf.angabe: Matthias Steinmetz and Matthias Bartelmann
• Umfang: 9 S.
• Fussnoten: Gesehen am 29.09.2017
• Titel Quelle: Enthalten in: Royal Astronomical Society: Monthly notices of the Royal Astronomical Society
• Jahr Quelle: 1995
• Band/Heft Quelle: 272(1995), 3, S. 570-578
• ISSN Quelle: 1365-2966
• DOI: doi:10.1093/mnras/272.3.570
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1563980134

Abstract

The study by White on the growth of angular momentum in dark haloes is extended towards a more detailed investigation of the spin parameter $$\lambda\equiv L\sqrt{E}/GM^{2.5}$$. Starting from the Zel'dovich approximation to structure formation, a dark halo is approximated by a homogeneous ellipsoid with the inertial tensor of the (highly irregular) Lagrangian region $$\Upsilon$$ from which the dark halo forms. Within this approximation, an expression for the spin parameter can be derived, which depends on the geometry of $$\Upsilon$$,the cosmological density parameter Ω0, the overdensity of the dark halo, and the tidal torque exerted on it. For Gaussian random fields, this expression can be evaluated statistically. As a result,we derive a probability distribution of the spin parameter which gives $$\lambda\simeq0.07_{-0.05}^{+0.04}$$, consistent with numerical investigations. This probability distribution steeply rises with increasing spin parameter, reaching its maximum at $$\lambda\simeq0.025$$. The 10 (50, 90) percentile values are λ = 0.02 (0.05, 0.11, respectively). There is a weak anticorrelation of the spin parameter with the peak height ν of the density fluctuation field, $$\lambda\propto v^{-0.29}$$. The dependence on Ω0 and the variance σ of the density-contrast field is very weak; there is only a marginal tendency for the spin parameter to be slightly larger for late-forming objects in an open universe. Due to the weak dependence on σ, our results should be quite generally applicable and independent of the special type of the fluctuation spectrum.