Systematic effects on the genus topology of the large-scale structure of the universe

Abstract

The large-scale structure of the universe is a useful cosmological probe of primordial non-Gaussianity and the expansion history of the universe because its topology does not change with time in the linear regime in the standard paradigm of structure formation. However, when the topology of iso-density contour surfaces is measured from observational data, many systematic effects are introduced due to the finite size of pixels used to define the density field, nonlinear gravitational evolution, redshift space distortion, shot noise (discrete sampling), and bias in the distribution of the density field tracers. We study the various systematic effects on the genus curve to a great accuracy by using the Horizon Run 2 simulation of a ΛCDM cosmology. We numerically measure the genus curve from the gravitationally evolved matter and dark matter halo density fields. It is found that all the non-Gaussian deviations due to systematic effects can be modeled by using a few low-order Hermite polynomials from H 0 to H 4. We compare our results with analytic theories whenever possible, and find many new terms in the Hermite series that are making significant contributions to the non-Gaussian deviations. In particular, it is found that the amplitude drop of the genus curve due to the nonlinear gravitational evolution can be accurately modeled by two terms, H 0 and H 2, with both coefficients proportional to , the mean-square density fluctuation. © 2014. The American Astronomical Society. All rights reserved.