The Effects of Non‐Gaussian Initial Conditions on the Structure and Substructure of Cold Dark Matter Halos

Abstract

We study the structure and substructure of halos obtained in N-body simulations for a ÃCDM cosmology with non-Gaussian initial conditions. The initial statistics are lognormal in the gravitational potential field with positive (LN p ) and negative (LN n ) skewness; the sign of the skewness is conserved by the density field, and the power spectrum is the same for all the simulations. Our aim is not to test a given non-Gaussian statistics but to explore the generic effect of positive-and negative-skew statistics on halo properties. From our low-resolution simulations, we find that LN p (LN n ) halos are systematically more (less) concentrated than their Gaussian counterparts. This result is confirmed by our Milky Way-and cluster-sized halos resimulated with high resolution. In addition, they show inner density profiles that depend on the statistics: the innermost slopes of LN p (LN n ) halos are steeper (shallower) than those obtained from the corresponding Gaussian halos. A subhalo population embedded in LN p halos is more susceptible to destruction than its counterpart inside Gaussian halos. On the other hand, subhalos in LN n halos tend to survive longer than subhalos in Gaussian halos. The spin parameter probability distribution of LN p (LN n ) halos is skewed to smaller (larger) values with respect to the Gaussian case. Our results show how the statistics of the primordial density field can influence some halo properties, opening the possibility of constraining, albeit indirectly, the primordial statistics at small scales.

Cosmic shear statistics in cosmologies with non-Gaussian initial conditions

“…As mentioned in , it is possible that this internal structure is different in non‐Gaussian with respect to Gaussian models. For instance, there has been some indication in the literature that the concentration and/or inner logarithmic slope of dark matter haloes in cosmological models with primordial non‐Gaussianity and positive skewness is larger than in the standard ΛCDM cosmology (Avila‐Reese et al 2003). This is intuitively in agreement with the fact that in such models it is easier to have high‐density peaks, which should cross earlier the threshold for collapse, with the corresponding structures having more time to relax and compactify.…”

The case for non-Gaussianity on cluster scales

“…They are expected by Amara & Refregier (2004) to yield constraints at a level similar to those set by current all‐sky CMB maps on very large scales. In addition, both the inner density profiles of large dark matter haloes and the abundance of substructure are sensitive to the sign of the skewness of the primordial gravitational potential field (Avila‐Reese et al 2003). Finally, new measurements of the 2 and n ‐point correlation function of local galaxy clusters of different masses will also set tight constraints.…”

“…Note that more speculative topics such as the periodicity noted by Broadhurst et al (1990), the presence of large regions underdense in galaxies (Frith et al 2003) or the high correlation length of very massive X‐ray clusters could also hint at primordial non‐Gaussianity. Note also that scale‐dependent non‐Gaussianity has been advocated by Avelino & Liddle (2004) and Chen et al (2003) as a possible way to reconcile the high optical depth to reionization with realistic efficiencies for the formation of the first stars, and that its possible impact on the inner profiles of dark‐matter haloes has been addressed by Avila‐Reese et al (2003).…”

What is the largest Einstein radius in the universe?

“…Since the concentrations of dark haloes are correlated with their mass assembly histories (Wechsler et al 2002), primordial non‐Gaussianities should have an impact on the halo concentration parameter as well. Indeed, N ‐body simulations done by Avila‐Reese et al (2003) showed that positive (negative) skewness in the initial density field results in larger (smaller) halo concentrations. We crudely include this effect by modifying the linear overdensity in as follows (Matarrese et al 2000): …”