Concentration, Spin and Shape of Dark Matter Haloes as a Function of the Cosmological Model: WMAP1, WMAP3 and WMAP5 results

Abstract

We investigate the effects of changes in the cosmological parameters between the WMAP 1st, 3rd, and 5th year results on the structure of dark matter haloes. We use a set of simulations that cover 5 decades in halo mass ranging from the scales of dwarf galaxies (V_c ~30 km/s) to clusters of galaxies (V_c ~ 1000 km/s). We find that the concentration mass relation is a power law in all three cosmologies. However the slope is shallower and the zero point is lower moving from WMAP1 to WMAP5 to WMAP3. For haloes of mass log(M_200/Msun) = 10, 12, and 14 the differences in the concentration parameter between WMAP1 and WMAP3 are a factor of 1.55, 1.41, and 1.29, respectively. As we show, this brings the central densities of dark matter haloes in good agreement with the central densities of dwarf and low surface brightness galaxies inferred from their rotation curves, for both the WMAP3 and WMAP5 cosmologies. We also show that none of the existing toy models for the concentration-mass relation can reproduce our simulation results over the entire range of masses probed. In particular, the model of Bullock et al (B01) fails at the higher mass end (M > 1e13 Msun), while the NFW model of Navarro, Frenk & White (1997) fails dramatically at the low mass end (M < 1e12 Msun). We present a new model, based on a simple modification of that of B01, which reproduces the concentration-mass relations in our simulations over the entire range of masses probed (1e10 Msun < M < 1e15 Msun). Haloes in the WMAP3 cosmology (at a fixed mass) are more flatted compared to the WMAP1 cosmology, with a medium to long axis ration reduced by ~10 %. Finally, we show that the distribution of halo spin parameters is the same for all three cosmologies.