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In order to probe modifications of gravity at cosmological scales, one needs accurate theoretical predictions. N-body simulations are required to explore the non-linear regime of structure formation but are very time consuming. In this work, we release a new public emulator, dubbed e-mantis , that performs an accurate and fast interpolation between the predictions of f (R) modified gravity cosmological simulations, run with ecosmog. We sample a wide 3D parameter space given by the current background scalar field value |$10^{-7}\lt \left|f_{R_0}\right|\lt 10^{-4}$|⁠ , matter density 0.24 < Ωm < 0.39, and primordial power spectrum normalization 0.6 < σ8 < 1.0, with 110 points sampled from a Latin hypercube. For each model we perform pairs of f (R)CDM and ΛCDM simulations covering an effective volume of |$\left(560 \, h^{-1}\, \mathrm{Mpc}\right)^3$| with a mass resolution of ∼2 × 1010 h −1 M ⊙. We build an emulator for the matter power spectrum boost B (k) = P f (R)(k)/ P ΛCDM(k) using a Gaussian process regression method. The boost is mostly independent of h, ns , and Ω b , which reduces the dimensionality of the relevant cosmological parameter space. Additionally, it is more robust against statistical and systematic errors than the raw power spectrum, thus strongly reducing our computational needs. According to our dedicated study of numerical systematics, the resulting emulator has an estimated maximum error of 3 per cent across the whole cosmological parameter space, for scales |$0.03 \ h\, \mathrm{Mpc}^{-1} \lt k \lt 7 \ h\, \mathrm{Mpc}^{-1}$|⁠ , and redshifts 0 < z < 2, while in most cases the accuracy is better than 1 per cent. Such an emulator could be used to constrain f (R) gravity with weak lensing analyses. [ABSTRACT FROM AUTHOR]

Recent determinations of the mean free path of ionizing photons (mfp) in the intergalactic medium (IGM) at z = 6 are lower than many theoretical predictions. In order to gain insight, we investigate the evolution of the mfp in our new massive fully coupled radiation-hydrodynamics cosmological simulation of reionization: Cosmic Dawn III (CoDa III). CoDa III's scale (⁠|$\rm 94^3 \, cMpc^3$|⁠) and resolution (⁠|$\rm 8192^3$| grid) make it particularly suitable to study the IGM during reionization. The simulation was performed with ramses - cudaton on Summit, and used 13 1072 processors coupled to 24 576 GPUs, making it the largest reionization simulation, and largest ever ramses simulation. A superior agreement with global constraints on reionization is obtained in CoDa III over Cosmic Dawn II (CoDa II), especially for the evolution of the neutral hydrogen fraction and the cosmic photoionization rate, thanks to an improved calibration, later end of reionization (z = 5.6), and higher spatial resolution. Analysing the mfp, we find that CoDa III reproduces the most recent observations very well, from z = 6 to z = 4.6. We show that the distribution of the mfp in CoDa III is bimodal, with short (neutral) and long (ionized) mfp modes, due to the patchiness of reionization and the coexistence of neutral versus ionized regions during reionization. The neutral mode peaks at sub-kpc to kpc scales of mfp, while the ionized mode peak evolves from 0.1 Mpc  h −1 at z = 7 to ∼10 Mpc  h −1 at z = 5.2. Computing the mfp as the average of the ionized mode provides the best match to the recent observational determinations. The distribution reduces to a single neutral (ionized) mode at z > 13 (z < 5). [ABSTRACT FROM AUTHOR]

Future galaxy surveys will provide accurate measurements of the matter power spectrum across an unprecedented range of scales and redshifts. The analysis of these data will require one to accurately model the imprint of non-linearities of the matter density field. In particular, these induce a non-Gaussian contribution to the data covariance that needs to be properly taken into account to realize unbiased cosmological parameter inference analyses. Here, we study the cosmological dependence of the matter power spectrum covariance using a dedicated suite of N -body simulations, the Dark Energy Universe Simulation–Parallel Universe Runs (DEUS-PUR) Cosmo. These consist of 512 realizations for 10 different cosmologies where we vary the matter density Ω m , the amplitude of density fluctuations σ8, the reduced Hubble parameter h , and a constant dark energy equation of state w by approximately |$10{{\ \rm per\ cent}}$|⁠. We use these data to evaluate the first and second derivatives of the power spectrum covariance with respect to a fiducial Λ-cold dark matter cosmology. We find that the variations can be as large as |$150{{\ \rm per\ cent}}$| depending on the scale, redshift, and model parameter considered. By performing a Fisher matrix analysis we explore the impact of different choices in modelling the cosmological dependence of the covariance. Our results suggest that fixing the covariance to a fiducial cosmology can significantly affect the recovered parameter errors and that modelling the cosmological dependence of the variance while keeping the correlation coefficient fixed can alleviate the impact of this effect. [ABSTRACT FROM AUTHOR]

Redshift-space distortions (RSD) in galaxy redshift surveys generally break both the isotropy and homogeneity of galaxy distribution. While the former aspect is particularly highlighted as a probe of growth of structure induced by gravity, the latter aspect, often quoted as wide-angle RSD but ignored in most of the cases, will become important and critical to account for as increasing the statistical precision in next-generation surveys. However, the impact of wide-angle RSD has been mostly studied using linear perturbation theory. In this paper, employing the Zel'dovich approximation, i.e. first-order Lagrangian perturbation theory for gravitational evolution of matter fluctuations, we present a quasi-linear treatment of wide-angle RSD, and compute the cross-correlation function. The present formalism consistently reproduces linear theory results, and can be easily extended to incorporate relativistic corrections (e.g. gravitational redshift). [ABSTRACT FROM AUTHOR]

The apparent distribution of large-scale structures in the Universe is sensitive to the velocity/potential of the sources as well as the potential along the line of sight through the mapping from real space to redshift space (redshift-space distortions, RSD). Since odd multipoles of the halo cross-correlation function vanish when considering standard Doppler RSD, the dipole is a sensitive probe of relativistic and wide-angle effects. We build a catalogue of ten million haloes (Milky Way size to galaxy-cluster size) from the full-sky light cone of a new 'RayGalGroupSims' N -body simulation which covers a volume of (2.625  h −1 Gpc)3 with 40963 particles. Using ray-tracing techniques, we find the null geodesics connecting all the sources to the observer. We then self-consistently derive all the relativistic contributions (in the weak-field approximation) to RSD: Doppler, transverse Doppler, gravitational, lensing and integrated Sachs–Wolfe. It allows us, for the first time, to disentangle all contributions to the dipole from linear to non-linear scales. At large scale, we recover the linear predictions dominated by a contribution from the divergence of neighbouring line of sights. While the linear theory remains a reasonable approximation of the velocity contribution to the dipole at non-linear scales it fails to reproduce the potential contribution below 30–60  h −1 Mpc (depending on the halo mass). At scales smaller than ∼10  h −1 Mpc, the dipole is dominated by the asymmetry caused by the gravitational redshift. The transition between the two regimes is mass dependent as well. We also identify a new non-trivial contribution from the non-linear coupling between potential and velocity terms. [ABSTRACT FROM AUTHOR]

The environmental dependence of galaxy clustering encodes information about the physical processes governing the growth of cosmic structure. We analyse the baryon acoustic peak as a function of environment in the galaxy correlation function of the Baryon Oscillation Spectroscopic Survey CMASS sample. Dividing the sample into three sub-sets by smoothed local overdensity, we detect acoustic peaks in the six separate autocorrelation and cross-correlation functions of the sub-samples. Fitting models to these correlation functions, calibrated by mock galaxy and dark matter catalogues, we find that the inferred distance scale is independent of environment, and consistent with the result of analysing the combined sample. The shape of the baryon acoustic feature, and the accuracy of density-field reconstruction in the Zeldovich approximation, varies with environment. By up-weighting underdense regions and down-weighting overdense regions in their contribution to the full-sample correlation function, by up to |$50{{\ \rm per\ cent}}$|⁠, we achieve a fractional improvement of a few per cent in the precision of baryon acoustic oscillation fits to the CMASS data and mock catalogues: the scatter in the preferred-scale fits to the ensemble of mocks improves from |$1.45{{\ \rm per\ cent}}$| to |$1.34{{\ \rm per\ cent}}$| (pre-reconstruction) and |$1.03{{\ \rm per\ cent}}$| to |$1.00{{\ \rm per\ cent}}$| (post-reconstruction). These results are consistent with the notion that the acoustic peak is sharper in underdense environments. [ABSTRACT FROM AUTHOR]

The upcoming generation of galaxy surveyswill probe the distribution ofmatter in the Universe with unprecedented accuracy. Measurements of the matter power spectrum at different scales and red shifts will provide stringent constraints on the cosmological parameters. However, on non-linear scales this will require an accurate evaluation of the covariance matrix. Here, we compute the covariance matrix of the three-dimensional matter density power spectrum for the concordance ΛCDM cosmology from an ensemble of N-body simulations of the Dark Energy Universe Simulation - Parallel Universe Runs (DEUS-PUR). This consists of 12 288 realizations of a (656 h-1 Mpc)3 simulation box with 2563 particles. We combine this set with an auxiliary sample of 96 simulations of the same volume with 10243 particles. We find the N-body mass resolution effect to be an important source of systematic errors on the covariance at high redshift and small intermediate scales. We correct for this effect by introducing an empirical statistical method which provide an accurate determination of the covariance matrix over a wide range of scales including the baryon oscillations interval. Contrary to previous studies that used smaller N-body ensembles, we find the power spectrum distribution to significantly deviate from expectations of a Gaussian random density field at k ≳ 0.25 h Mpc-1 and z < 0.5. This suggests that for the finite-volume surveys, an unbiased estimate of the ensemble-averaged band power at these scales and red shifts may require a more careful assessment of non-Gaussian errors than previously considered. [ABSTRACT FROM AUTHOR]

ABSTRACT The universality of the halo mass function is investigated in the context of dark energy cosmologies. This widely used approximation assumes that the mass function can be expressed as a function of the matter density Ωm and the root-mean-square linear density fluctuation σ only, with no explicit dependence on the properties of dark energy or redshift. In order to test this hypothesis, we run a series of 15 high-resolution N-body simulations for different cosmological models. These consist of three Λ cold dark matter cosmologies' best-fitting Wilkinson Microwave Anisotropy Probe 1-, 3- and 5-yr data, which are used for model comparison, and three toy models characterized by a Ratra-Peebles quintessence potential with different slopes and amounts of dark energy density. These toy models have very different evolutionary histories at the background and linear levels, but share the same σ8 value. For each of these models, we measure the mass function from catalogues of haloes identified in the simulations using the Friend-of-Friend (FoF) algorithm. We find redshift-dependent deviations from a universal behaviour, well above numerical uncertainties and of non-stochastic origin, which are correlated with the linear growth factor of the investigated cosmologies. Using the spherical collapse as guidance, we show that such deviations are caused by the cosmology dependence of the non-linear collapse and virialization process. For practical applications, we provide a fitting formula of the mass function accurate to 5 per cent for all investigated cosmologies. We also derive an empirical relation between the FoF linking parameter and the virial overdensity which can account for most of the deviations from an exact universal behaviour. Overall, these results suggest that measurements of the halo mass function at z= 0 can provide additional constraints on dark energy since it carries a fossil record of the past cosmic evolution. [ABSTRACT FROM AUTHOR]

Quintessence has been proposed to account for dark energy (DE) in the Universe. This component causes a typical modification of the background cosmic expansion, which, in addition to its clustering properties, can leave a potentially distinctive signature on large-scale structures. Many previous studies have investigated this topic, particularly in relation to the non-linear regime of structure formation. However, no careful pre-selection of viable quintessence models with high precision cosmological data was performed. Here we show that this has led to a misinterpretation (and underestimation) of the imprint of quintessence on the distribution of large-scale structures. To this purpose, we perform a likelihood analysis of the combined Supernova Ia UNION data set and Wilkinson Microwave Anisotropy Probe 5-yr data to identify realistic quintessence models. These are specified by different model parameter values, but still statistically indistinguishable from the vanilla Λ cold dark matter (ΛCDM). Differences are especially manifest in the predicted amplitude and shape of the linear matter power spectrum though these remain within the uncertainties of the Sloan Digital Sky Survey data. We use these models as a benchmark for studying the clustering properties of dark matter haloes by performing a series of high-resolution N-body simulations. In this first paper, we specifically focus on the non-linear matter power spectrum. We find that realistic quintessence models allow for relevant differences of the dark matter distribution with respect to the ΛCDM scenario well into the non-linear regime, with deviations of up to 40 per cent in the non-linear power spectrum. Such differences are shown to depend on the nature of DE, as well as the scale and epoch considered. At small scales ( , depending on the redshift), the structure formation process is about 20 per cent more efficient than in ΛCDM. We show that these imprints are a specific record of the cosmic structure formation history in DE cosmologies and therefore cannot be accounted for in standard fitting functions of the non-linear matter power spectrum. [ABSTRACT FROM AUTHOR]