Dark matter halos: Velocity anisotropy-density slope relation

作者：Zait Amir^*; Hoffman Yehuda; Shlosman Isaac

来源：Astrophysical Journal, 2008, 682(2): 835-840.

DOI：10.1086/589431

• dark matter
• galaxies : clusters : general
• galaxies : evolution
• galaxies : formation
• galaxies : halos
• galaxies : kinematics and dynamics

Dark matter (DM) halos formed in CDM cosmologies seem to be characterized by a power-law phase-space density profile. The density of the DM halos is often fitted by the NFW profile but a better fit is provided by the Sersic fitting formula. These relations are empirically derived from cosmological simulations of structure formation but have not yet been explained on a first-principle basis. Here we solve the Jeans equation under the assumption of a spherical DM halo in dynamical equilibrium, that obeys a power-law phase-space density and either the NFW-like or the Sersic density profile. We then calculate the velocity anisotropy, beta(r), analytically. Our main result is that for the NFW-like profile the beta-gamma relation is not a linear one ( where gamma is the logarithmic derivative of the density rho[r]). The shape of beta(r) depends mostly on the ratio of the gravitational to kinetic energy within the NFW scale radius R-s. For the Sersic profile a linear beta-gamma relation is recovered, and in particular for the Sersic index of n approximate to 6.0 case the linear fit of Hansen & Moore is reproduced. Our main result is that the phase-space density power law, the Sersic density form, and the linear beta-gamma dependence constitute a consistent set of relations which obey the spherical Jeans equation and as such provide the framework for the dynamical modeling of DM halos.

• 出版日期2008-8-1