The contributions of matter inside and outside of haloes to the matter power spectrum

Halo-based models have been successful in predicting the clustering of matter. However, 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-virialized matter might contribute significantly to the non-linear clustering signal. Here, we investigate the contribution of haloes to the matter power spectrum as a function of both scale and halo mass by combining a set of cosmological N-body simulations to calculate the contributions of different spherical overdensity regions, Friends-of-Friends (FoF) groups and matter outside haloes to the power spectrum. We find that matter inside spherical overdensity regions of size R-200,R-mean cannot account for all power for 1 less than or similar to k <= 100 h Mpc(-1), regardless of the minimum halomass. At most, it accounts for 95 per cent of the power (k greater than or similar to 20 h Mpc(-1)). For 2 less than or similar to k less than or similar to 10 h Mpc(-1), haloes with mass M-200,M-mean less than or similar to 1011 h(-1) M-circle dot contribute negligibly to the power spectrum, and our results appear to be converged with decreasing halo mass. When haloes are taken to be regions of size R-200,R-crit, the amount of power unaccounted for is larger on all scales. Accounting also for matter inside FoF groups but outside R-200,R-mean increases the contribution of halo matter on most scales probed here by 5-15 per cent. Matter inside FoF groups with M-200,M-mean > 10(9) h(-1) M-circle dot accounts for essentially all power for 3 < k < 100 h Mpc(-1). We therefore expect halo models that ignore the contribution of matter outside R-200,R-mean to overestimate the contribution of haloes of any mass to the power on small scales (k greater than or similar to 1 h Mpc(-1)).