Constraining primordial non-Gaussianity with moments of the large-scale density field

Abstract

We use cosmological N-body simulations to investigate whether measurements of the moments of large-scale structure can yield constraints on primordial non-Gaussianity. We measure the variance, skewness, and kurtosis of the evolved density field from simulations with Gaussian and three different non-Gaussian initial conditions: a local model with fNL = 100, an equilateral model with fNL = −400, and an orthogonal model with fNL = −400. We show that the moments of the dark matter density field differ significantly between Gaussian and non-Gaussian models. We also make the measurements on mock galaxy catalogues that contain galaxies with clustering properties similar to those of luminous red galaxies. We find that, in the case of skewness and kurtosis, galaxy bias reduces the detectability of non-Gaussianity. However, in the case of the variance, galaxy bias greatly amplifies the detectability of non-Gaussianity. In all cases, we find that redshift distortions do not significantly affect the detectability. When we restrict our measurements to volumes equivalent to the Sloan Digital Sky Survey II or Baryon Oscillation Spectroscopic Survey samples, the probability of detecting a departure from the Gaussian model is high by using measurements of the variance, but very low by using only skewness and kurtosis. We estimate that in order to detect an amount of non-Gaussianity that is consistent with recent cosmic microwave background constraints using skewness or kurtosis, we would need a galaxy survey that is much larger than any planned future survey. However, future surveys should be large enough to place meaningful constraints using galaxy variance measurements.