Density profiles of dark matter haloes: diversity and dependence on environment

We study the outer density profiles of dark matter haloes predicted by a generalized secondary infall model and observed in a dissipationless cosmological simulation of a low-density flat cold dark matter model with the cosmological constant. We find substantial systematic variations in shapes and concentrations of the halo profiles as well as a strong correlation of the profiles with the environment in which the haloes are embedded. In the N-body simulation, the average outer slope of the density profiles, beta (rho proportional to r(-beta)), of isolated haloes is beta approximate to 2.9, and 68 per cent of these haloes have values of beta between 2.5 and 3.8. Haloes in dense environments of clusters are more concentrated and exhibit a broad distribution of beta with an average value higher than the average beta for isolated haloes. For haloes located within half the virial radius of the cluster from the centre values beta approximate to 4 are very common. Contrary to what one may expect, the haloes contained within groups and galaxy systems are less concentrated and have flatter outer density profiles than the isolated haloes: the distribution of beta peaks at approximate to 2.3-2.7. The slope beta weakly anticorrelates with the halo mass M-h. The concentration decreases with M-h, but its scatter is roughly equal to the whole variation of this parameter in the galaxy halo mass range. The mass and circular velocity of the haloes are strongly correlated, M-h proportional to Vm alpha, with alpha approximate to 3.3 and approximate to 3.5 for the isolated haloes and haloes in clusters, respectively. For M-h approximate to 10(12) h(-1) M-circle dot the rms deviations from these relations are Delta log M-h = 0.12 and 0.18, respectively. Approximately 30 per cent of the haloes are contained within larger haloes or have massive companions within three virial radii. The companions are allowed to have masses larger than similar to 0.3 times the mass of the current halo. The remaining 70 per cent of the haloes are isolated objects. We find that the distribution of beta as well as the concentration-mass and M-h-V-m relations for the isolated haloes agree very well with the predictions of our seminumerical approach, which is based on a generalization of the secondary infall model and on the extended Press-Schechter formalism.