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ABSTRACT We study the concentration of dark matter haloes and its evolution in N-body simulations of the standard Λ cold dark matter (ΛCDM) cosmology. The results presented in this paper are based on four large N-body simulations with ∼10 billion particles each: the Millennium-I and -II, Bolshoi and MultiDark simulations. The MultiDark (or BigBolshoi) simulation is introduced in this paper. This suite of simulations with high mass resolution over a large volume allows us to compute with unprecedented accuracy the concentration over a large range of scales (about six orders of magnitude in mass), which constitutes the state of the art of our current knowledge on this basic property of dark matter haloes in the ΛCDM cosmology. We find that there is consistency among the different simulation data sets, despite the different codes, numerical algorithms and halo/subhalo finders used in our analysis. We confirm a novel feature for halo concentrations at high redshifts: a flattening and upturn with increasing mass. The concentration c( M, z) as a function of mass and the redshift and for different cosmological parameters shows a remarkably complex pattern. However, when expressed in terms of the linear rms fluctuation of the density field σ( M, z), the halo concentration c(σ) shows a nearly universal simple U-shaped behaviour with a minimum at a well-defined scale at σ∼ 0.71. Yet, some small dependences with redshift and cosmology still remain. At the high-mass end (σ < 1), the median halo kinematic profiles show large signatures of infall and highly radial orbits. This c-σ( M, z) relation can be accurately parametrized and provides an analytical model for the dependence of concentration on halo mass. When applied to galaxy clusters, our estimates of concentrations are substantially larger - by a factor up to 1.5 - than previous results from smaller simulations, and are in much better agreement with results of observations. [ABSTRACT FROM AUTHOR]

We present a general analytical formalism to calculate accurately several statistics related to underdense regions in the Universe. The statistics are computed for dark matter halo and galaxy distributions both in real space and redshift space at any redshift. Using this formalism, we found that void statistics for galaxy distributions can be obtained, to a very good approximation, assuming galaxies to have the same clustering properties as haloes above a certain mass. We deduced a relationship between this mass and that of haloes with the same accumulated number density as the galaxies. We also found that the dependence of void statistics on redshift is small. For instance, the number of voids larger than (defined to not contain galaxies brighter than ) change less than 20 per cent between and 0. However, the dependence of void statistics on σ8 and Γ is considerably larger, making them appropriate to develop tests to measure these parameters. We have shown how to efficiently construct several of these tests and discussed in detail the treatment of several observational effects. The formalism presented here along with the observed statistics extracted from current and future large galaxy redshift surveys will provide an independent measurement of the relevant cosmological parameters. Combining these measurements with those found using other methods will contribute to reduce their uncertainties. [ABSTRACT FROM AUTHOR]

The unconditional mass function (UMF) of dark matter haloes has been determined accurately in the literature, showing excellent agreement with high-resolution numerical simulations. However, this is not the case for the conditional mass function (CMF). Here, we propose a simple analytical procedure to derive the CMF by rescaling the UMF to the constrained environment using the appropriate mean and variance of the density field at the constrained point. This method introduces two major modifications with respect to the standard rescaling procedure. First of all, rather than using in the scaling procedure the properties of the environment averaged over all the conditioning regions, we implement the rescaling locally. We show that for high masses this modification may lead to substantially different results. Secondly, we modify the (local) standard rescaling procedure in such a manner as to force normalization, in the sense that when one integrates the CMF over all possible values of the constraint multiplied by their corresponding probability distribution, the UMF is recovered. In practice, we do this by replacing in the standard procedure the value (the linear density contrast for collapse) by certain adjustable effective parameter . In order to test the method, we compare our prescription with the results obtained from numerical simulations in voids. We find that when our modified rescaling is applied locally to any existing numerical fit of the UMF, and the appropriate value for is chosen, the resulting CMF is, in all cases, in very good agreement with the numerical results. Based on these results, we finally present a very accurate analytical fit to the (accumulated) CMF obtained with our procedure, as a function of the parameters that describe the conditioning region (size and mean linear density contrast), the redshift and the relevant cosmological parameters (σ8 and Γ). This analytical fit may be useful for any theoretical treatment of the large-scale structure, and has been already used successfully in regard with the statistic of voids. [ABSTRACT FROM AUTHOR]

Using the high-resolution cosmological N-body simulation MareNostrum universe we study the orientation of shape and angular momentum of galaxy-size dark matter haloes around large voids. We find that haloes located on the shells of the largest cosmic voids have angular momenta that tend to be preferentially perpendicular to the direction that joins the centre of the halo and the centre of the void. This alignment has been found in spiral galaxies around voids using galaxy redshift surveys. We measure for the first time the strength of this alignment, showing how it falls off with increasing distance to the centre of the void. We also confirm the correlation between the intensity of this alignment and the halo mass. The analysis of the orientation of the halo main axes confirms the results of previous works. Moreover, we find a similar alignment for the baryonic matter inside dark matter haloes, which is much stronger in their inner parts. [ABSTRACT FROM AUTHOR]