Day 824

Tuesday.

1501.05950
The contributions of matter inside and outside of haloes to the matter power spectrum
van Daalen, Schaye

Halo-based models have been successful in predicting the clustering of matter, but the validity of the postulate that the clustering is fully determined by matter inside haloes remains largely untested, and it is not clear a priori whether non-virialised matter might contribute significantly to the NL clustering signal.  Investigate the contribution of haloes to the matter PS as a function of both sale and halo mass by combining a set of cosmo N-body sims to calculate the contributions of different spherical overdensity regions, FoF groups and matter outside haloes to the PS.  Find that matter inside spherical overdensity regions of size R200m cannot account for all power for 1<k<100 h/Mpc, regardless of the minimum halo mass.  At most, it accounts for 95% of the power (k>20 h/Mpc).  For 2<k<10 h/Mpc, haloes with mass M200m<1e11 Msunh contribute negligibly to the PS, and the results appear to be converged with decreasing halo mass.  When haloes are taken to be regions of size R020c, the amount of power unaccounted for is larger on all scales.  Accounting also for matter inside for groups but outside R200m increases the contribution of halo matter on most scales probed here by 5-15%.  Matter inside FoF groups with M200m>1e9 Msun/h accounts for essentially all power for 3<k<100 h/Mpc.  Therefore expect halo models that ignore the contribution of matter outside R200m to overestimate the contribution of haloes of any mass to the power on small scales (k>1 h/Mpc).