Mock galaxy catalogs using the quick particle mesh method

Sophisticated analysis of modern large-scale structure surveys requires mock catalogs. Mock catalogs are used to optimize survey design, test reduction and analysis pipelines, make theoretical predictions for basic observables and propagate errors through complex analysis chains. We present a new method, which we call "quick particle mesh", for generating many large-volume, approximate mock catalogs at low computational cost. The method is based on using rapid, low-resolution particle mesh simulations that accurately reproduce the large-scale dark matter density field. Particles are sampled from the density field based on their local density such that they have N-point statistics nearly equivalent to the halos resolved in high-resolution simulations, creating a set of mock halos that can be populated using halo occupation methods to create galaxy mocks for a variety of possible target classes.Comment: 13 pages, 16 figures. Matches version accepted by MNRAS. Code available at http://github.com/mockFactor

Tests of redshift-space distortions models in configuration space for the analysis of the BOSS final data release

Observations of redshift-space distortions in spectroscopic galaxy surveys offer an attractive method for observing the build-up of cosmological structure, which depends both on the expansion rate of the Universe and our theory of gravity. In preparation for analysis of redshift-space distortions from the Baryon Oscillation Spectroscopic Survey (BOSS) final data release we compare a number of analytic and phenomenological `streaming' models, specified in configuration space, to mock catalogs derived in different ways from several N-body simulations. The galaxies in each mock catalog have properties similar to those of the higher redshift galaxies measured by BOSS but differ in the details of how small-scale velocities and halo occupancy are determined. We find that all of the analytic models fit the simulations over a limited range of scales while failing at small scales. We discuss which models are most robust and on which scales they return reliable estimates of the rate of growth of structure: we find that models based on some form of resummation can fit our N-body data for BOSS-like galaxies above $30\,h^{-1}$Mpc well enough to return unbiased parameter estimates.Comment: 12 pages, 11 figures, matches version accepted by MNRA

Our Non-Gaussian Universe: Higher Order Correlation Functions in the Sloan Digital Sky Survey

Modern galaxy surveys, such as the Sloan Digital Sky Survey (SDSS), provide a wealth of information about large scale structure, galaxy evolution and cosmology. Even if initial density fluctuations were extremely Gaussian, gravitational collapse predicts the growth of non-Gaussianities in the galaxy distribution. Higher order clustering statistics, such as the three-point correlation function (3PCF), are necessary to probe the non-Gaussian structure and shape information in these distributions. We measure the clustering of spectroscopic galaxies in the SDSS Main Galaxy Sample, focusing on the shape or configuration dependence of the 3PCF in redshift and projected space. This work constitutes the largest observational dataset ever used to investigate the 3PCF, and the only known projected measurement for SDSS galaxies.The 3PCF exhibits extreme sensitivity to systematic effects such as sky completeness, binning scheme and insufficient error resolution. We show these systematics can dramatically affect our results, which are not consistently accounted for in comparable analyses.We find significant configuration dependence of the 3PCF on intermediate to large scales (3-27 Mpc/h), in agreement with predictions from LCDM and disagreement with the hierarchical ansatz. Below 6 Mpc/h, the redshift space 3PCF shows reduced power and weak configuration dependence in comparison with projected measurements. Our results indicate that redshift distortions, and not galaxy bias, can make the 3PCF appear consistent with the hierarchical ansatz.Compared to the lower order 2PCF, the 3PCF shows a weaker dependence on luminosity with no significant dependence on scales above 9 Mpc/h. On scales less than 9 Mpc/h, the 3PCF shows a greater dependence on color than on luminosity.We conclude that galaxies remain a biased tracer of the mass with a stronger bias associated with greater luminosity. Using a thorough error analysis in the linear regime 9-27 Mpc/h, we show bright galaxies are a biased realization of mass clustering at greater than 4.5 sigma in redshift space and 2.5 sigma in projected space. The strong degeneracy between linear and quadratic bias terms naturally explains the weak luminosity dependence of the 3PCF. Contrary to some claims, we find linear bias is sufficient to explain galaxy-mass bias of our samples