Galaxy clustering in standard and non-standard cosmologies

We study the formation, evolution and clustering of galaxies in standard and modified gravity universes and prepare synthetic catalogues for future galaxy surveys, such as DESI. To do this, we have run and analysed N-body and hydrodynamical simulations of different gravity models. In the first part, we focus our attention on two of the most representative and popular families of modified gravity models: the Hu & Sawicki f(R) gravity and the normal-branch Dvali-Gabadadze-Porrati (nDGP) braneworld model. We use mock galaxy catalogues constructed from a halo occupation distribution (HOD) prescription with the HOD parameters in the modified gravity models tuned to match with the number density and the real-space clustering of BOSS-CMASS galaxies to analyse the marked correlation function in three variants of the f(R) gravity model and to measure galaxy clustering in redshift space in both f(R) and nDGP models. In addition, we introduce the first set of full-hydrodynamical simulations of galaxy formation in the nDGP model using a new modified version of the AREPO code and the IllustrisTNG galaxy formation model. In the second half, we explore if there is an optimal way to select a galaxy sample in order to measure the baryon acoustic oscillation (BAO) scale, which is used as a standard ruler to constrain the cosmic expansion. Also, we present a covariance and clustering analysis of DESI-like luminous red galaxies (LRGs). For the latter, the mock catalogues are built with a novel technique using the semi-analytical model of galaxy formation GALFORM and a large number of halo catalogues generated using the Parallel-PM N-body GLAM code

MGLENS: Modified gravity weak lensing simulations for emulation-based cosmological inference

We present MGLENS, a large series of modified gravity lensing simulations tailored for cosmic shear data analyses and forecasts in which cosmological and modified gravity parameters are varied simultaneously. Based on the FORGE and BRIDGE N-body simulation suites presented in companion papers, we construct 100 × 5000 deg2 of mock Stage-IV lensing data from two 4D Latin hypercubes that sample cosmological and gravitational parameters in f(R) and nDGP gravity, respectively. These are then used to validate our inference analysis pipeline based on the lensing power spectrum, exploiting our implementation of these modified gravity models within the COSMOSIS cosmological inference package. Sampling this new likelihood, we find that cosmic shear can achieve 95 per cent CL constraints on the modified gravity parameters of log10[fR0 ] 0.09, after marginalizing over intrinsic alignments of galaxies and including scales up to = 5000. We also investigate the impact of photometric uncertainty, scale cuts, and covariance matrices. We finally explore the consequences of analysing MGLENS data with the wrong gravity model, and report catastrophic biases for a number of possible scenarios. The Stage-IV MGLENS simulations,the FORGE and BRIDGE emulators and the COSMOSIS interface modules will be made publicly available upon journal acceptance

Towards testing the theory of gravity with DESI: summary statistics, model predictions and future simulation requirements

Shortly after its discovery, General Relativity (GR) was applied to predict the behavior of our Universe on the largest scales, and later became the foundation of modern cosmology. Its validity has been verified on a range of scales and environments from the Solar system to merging black holes. However, experimental confirmations of GR on cosmological scales have so far lacked the accuracy one would hope for -- its applications on those scales being largely based on extrapolation and its validity sometimes questioned in the shadow of the unexpected cosmic acceleration. Future astronomical instruments surveying the distribution and evolution of galaxies over substantial portions of the observable Universe, such as the Dark Energy Spectroscopic Instrument (DESI), will be able to measure the fingerprints of gravity and their statistical power will allow strong constraints on alternatives to GR. In this paper, based on a set of N-body simulations and mock galaxy catalogs, we study the predictions of a number of traditional and novel estimators beyond linear redshift distortions in two well-studied modified gravity models, chameleon f(R) gravity and a braneworld model, and the potential of testing these deviations from GR using DESI. These estimators employ a wide array of statistical properties of the galaxy and the underlying dark matter field, including two-point and higher-order statistics, environmental dependence, redshift space distortions and weak lensing. We find that they hold promising power for testing GR to unprecedented precision. The major future challenge is to make realistic, simulation-based mock galaxy catalogs for both GR and alternative models to fully exploit the statistic power of the DESI survey and to better understand the impact of key systematic effects. Using these, we identify future simulation and analysis needs for gravity tests using DESI