Publications (2)10.21 Total impact
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ABSTRACT: The scaledependent galaxy bias generated by primordial nonGaussianity (PNG) can be used to detect and constrain deviations from standard singlefield inflation. The strongest signal is expected in the local model for PNG, where the amplitude of nonGaussianity can be expressed by a set of parameters (fnl, gnl, ...). Current observational constraints from galaxy clustering on fnl and gnl assume that the others PNG parameters are vanishing. Using two sets of cosmological Nbody simulations where both fnl and gnl are nonzero, we show that this strong assumption generally leads to biased estimates and spurious redshift dependencies of the parameters. Additionally, if the signs of fnl and gnl are opposite, the amplitude of the scaledependent bias is reduced, possibly leading to a false null detection. Finally we show that model selection techniques like the Bayesian evidence can (and should) be used to determine if more than one PNG parameter is required by the data.Monthly Notices of the Royal Astronomical Society 05/2012; 425(1). DOI:10.1111/j.17453933.2012.01305.x · 5.11 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We test thirdorder standard perturbation theory (SPT) as an approximation to nonlinear cosmological structure formation. A novel approach is used to numerically calculate the threedimensional dark matter density field using SPT from the initial conditions of two highresolution cosmological simulations. The calculated density field is compared to the nonlinear dark matter field of the simulations both pointbypoint and statistically. For smoothing scales above 8 Mpc/h it shows a good agreement up to redshift 0. We present a simple fitting formula to relate the linear and nonlinear density contrast that accurately recovers the nonlinear time evolution for 0 <= z <= 10 at the per cent level. To address the problem of biasing between the matter field and the haloes identified in the simulation, we employ the Eulerian local bias model (ELB), including nonlinear bias up to the third order. The bias parameters are obtained by fitting a scatter plot of halo and matter density (both from the simulation and from SPT). Using these bias parameters, we can reconstruct the halo density field. We find that this reconstruction is not able to capture all the details of the halo distribution. We investigate how well the large scale bias can be described by a constant and if it corresponds to the linear bias parameter b_1 of the local bias model. We also discuss how well the halohalo power spectrum and the halomass cross spectrum from the reconstructed halo density field agree with the corresponding statistics from the simulation. The results show that while SPT is an excellent approximation for the matter field for suitably large smoothing scales even at redshift 0, the ELB model can only account for some of the properties of the halo density field.Monthly Notices of the Royal Astronomical Society 01/2011; 415(1). DOI:10.1111/j.13652966.2011.18768.x · 5.11 Impact Factor
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27  Citations  
10.21  Total Impact Points  
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20112012

University of Bonn
 ArgelanderInstitute of Astronomy
Bonn, North RhineWestphalia, Germany
