A Universal Density Profile from Hierarchical Clustering
Abstract
We use highresolution Nbody simulations to study the equilibrium density profiles of dark matter halos in hierarchically clustering universes. We find that all such profiles have the same shape, independent of the halo mass, the initial density fluctuation spectrum, and the values of the cosmological parameters. Spherically averaged equilibrium profiles are well fitted over two decades in radius by a simple formula originally proposed to describe the structure of galaxy clusters in a cold dark matter universe. In any particular cosmology, the two scale parameters of the fit, the halo mass and its characteristic density, are strongly correlated. Lowmass halos are significantly denser than more massive systems, a correlation that reflects the higher collapse redshift of small halos. The characteristic density of an equilibrium halo is proportional to the density of the universe at the time it was assembled. A suitable definition of this assembly time allows the same proportionality constant to be used for all the cosmologies that we have tested. We compare our results with previous work on halo density profiles and show that there is good agreement. We also provide a stepbystep analytic procedure, based on the PressSchechter formalism, that allows accurate equilibrium profiles to be calculated as a function of mass in any hierarchical model.
 Publication:

The Astrophysical Journal
 Pub Date:
 December 1997
 DOI:
 10.1086/304888
 arXiv:
 arXiv:astroph/9611107
 Bibcode:
 1997ApJ...490..493N
 Keywords:

 Cosmology: Theory;
 Cosmology: Dark Matter;
 Galaxies: Halos;
 Methods: Numerical;
 Astrophysics
 EPrint:
 typos in eqs A5 and A14 corrected. In press in the ApJ, Dec 1, 1997. Full PS file with figures can be obtained from http://penedes.as.arizona.edu/~jfn/preprints/dprof.ps.gz