DARK MATTER HALOS IN THE STANDARD COSMOLOGICAL MODEL: RESULTS FROM THE BOLSHOI SIMULATION

Abstract

We present the first results from the new Bolshoi N-body cosmological LCDM\nsimulation that uses cosmological parameters favored by current observations.\nThe Bolshoi simulation was done in a volume 250Mpc on a side using 8billion\nparticles with mass and force resolution adequate to follow subhalos down to a\ncompleteness limit of Vcirc=50km/ s circular velocity. Using excellent\nstatistics of halos and subhalos (10M at every moment and 50M over the whole\nhistory) we present accurate approximations for statistics such as the halo\nmass function, the concentrations for distinct halos and subhalos, abundance of\nhalos as function of their circular velocity, the abundance and the spatial\ndistribution of subhalos. We find that at high redshifts the concentration\nfalls to a minimum of about 3.8 and then rises slightly for higher values of\nhalo mass. We find that while the Sheth-Tormen approximation for the mass\nfunction of halos found by spherical overdensity is accurate at low redshifts,\nit over-predicts the abundance of halos by nearly an order of magnitude by\nz=10. We find that the number of subhalos scales with the circular velocity of\nthe host halo as Vhost**0.5, and that subhalos have nearly the same radial\ndistribution as dark matter particles at radii 0.3-2 times the host halo virial\nradius. The subhalo velocity function n(>V) behaves as V**(-3). We give\nnormalization of this relation for different masses and redshifts. Finally, we\nuse an abundance-matching procedure to assign r-band luminosities to dark\nmatter halos as a function of halo Vcirc, and find that the luminosity-velocity\nrelation is in remarkably good agreement with the observed Tully-Fisher\nrelation for galaxies in the range 50-200km/s.\n