Inverted initial conditions: Exploring the growth of cosmic structure and voids

We present and test a method that dramatically reduces variance arising from the sparse sampling of wavemodes in cosmological simulations. The method uses two simulations which are fixed (the initial Fourier mode amplitudes are fixed to the ensemble average power spectrum) and paired (with initial modes exactly out of phase). We measure the power spectrum, monopole and quadrupole redshift-space correlation functions, halo mass function and reduced bispectrum at z = 1. By these measures, predictions from a fixed pair can be as precise on non-linear scales as an average over 50 traditional simulations. The fixing procedure introduces a non-Gaussian correction to the initial conditions; we give an analytic argument showing why the simulations are still able to predict the mean properties of the Gaussian ensemble. We anticipate that the method will drive down the computational time requirements for accurate large-scale explorations of galaxy bias and clustering statistics, enabling more precise comparisons with theoretical models, and facilitating the use of numerical simulations in cosmological data interpretation.

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“…The second of the pair of simulations is then generated by transforming θ i → π + θ i (Pontzen et al 2016).…”

Section: Numerical Simulationsmentioning

confidence: 99%

“…(i) use a fixed input power spectrum, meaning that we enforcê P L = P L when generating the initial conditions; (ii) are paired, so that a hierarchy of effects due to chance phase correlations can be cancelled (Pontzen et al 2016). …”

Section: Introductionmentioning

confidence: 99%

Cosmological N-body simulations with suppressed variance

Angulo

Pontzen

2016

Monthly Notices of the Royal Astronomical Society: Letters

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“…In [29], the Zel'dovich approximation was used to derive the cross-spectrum between two numerical simulations with inverted initial conditions. Here, we closely follow their approach to derive an expression for unequal time correlators of the matter power spectrum.…”

Section: Zel'dovich Approximationmentioning

confidence: 99%

“…Following a similar derivation to that of Appendix A of Ref. [29], we arrive at the following expression for the unequal time correlator in the Zel'dovich approximation,…”

Section: Zel'dovich Approximationmentioning

confidence: 99%

Unequal time correlators and the Zel’dovich approximation

Chisari

Pontzen

2019

Phys. Rev. D

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The modeling of cosmological observables is based on the statistics of the matter density, velocity and gravitational fields in the Universe as a function of time. Typically, calculations are restricted to "equal time" correlations, where any given fields are evaluated at the same redshift. For some applications, it is necessary to make accurate predictions of "unequal time correlators", where the fields considered are evaluated at different redshifts. In this work, we show that the Zel'dovich approximation provides an accurate (< 10%) analytical prescription to model unequal time correlators, which we validate against numerical N-body simulations. The Zel'dovich approximation introduces a scale-dependent exponential suppression of unequal time correlators, which depends on cosmology and the redshifts of the fields considered. Comparing the Zel'dovich case to previous approximations, we show that it can yield accurate predictions for wavenumbers that extend well into the nonlinear regime. However, we also show that correlations over such scales are typically suppressed by the geometry of the lightcone, and thus should normally be negligible for cosmology with galaxy surveys. We discuss potential exceptions, such as intrinsic galaxy alignments, where unequal time correlators could play a role in the modeling of the observables. * elisa.chisari@physics.ox.ac.uk † a.pontzen@ucl.ac.uk 1 http://www.lsst.org 2 sci.esa.int/euclid/ 3 http://WFIRST.gsfc.nasa.gov

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confidence: 99%

Comparing galaxy clustering in Horizon-AGN simulated light-cone mocks and VIDEO observations

Hatfield

Laigle

Jarvis

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Hydrodynamical cosmological simulations have recently made great advances in reproducing galaxy mass assembly over cosmic time -as often quantified from the comparison of their predicted stellar mass functions to observed stellar mass functions from data. In this paper we compare the clustering of galaxies from the hydrodynamical cosmological simulated lightcone Horizon-AGN, to clustering measurements from the VIDEO survey observations. Using mocks built from a VIDEO-like photometry, we first explore the bias introduced into clustering measurements by using stellar masses and redshifts derived from SED-fitting, rather than the intrinsic values. The propagation of redshift and mass statistical and systematic uncertainties in the clustering measurements causes us to underestimate the clustering amplitude. We find then that clustering and halo occupation distribution (HOD) modelling results are qualitatively similar in Horizon-AGN and VIDEO. However at low stellar masses Horizon-AGN underestimates the observed clustering by up to a factor of ∼3, reflecting the known excess stellar mass to halo mass ratio for Horizon-AGN low mass haloes, already discussed in previous works. This reinforces the need for stronger regulation of star formation in low mass haloes in the simulation. Finally, the comparison of the stellar mass to halo mass ratio in the simulated catalogue, inferred from angular clustering, to that directly measured from the simulation, validates HOD modelling of clustering as a probe of the galaxy-halo connection.

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Inverted initial conditions: Exploring the growth of cosmic structure and voids

Cited by 66 publications

References 51 publications

Cosmological N-body simulations with suppressed variance

Cosmological N-body simulations with suppressed variance

Unequal time correlators and the Zel’dovich approximation

Comparing galaxy clustering in Horizon-AGN simulated light-cone mocks and VIDEO observations

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