SIMBIG: A Forward Modeling Approach To Analyzing Galaxy Clustering

ChangHoon Hahn, Michael Eickenberg, Shirley Ho, Jiamin Hou, Pablo Lemos, Elena Massara, Chirag Modi, Azadeh Moradinezhad Dizgah, Bruno Régaldo-Saint Blancard, Muntazir M. Abidi

Submitted on 1 November 2022


We present the first-ever cosmological constraints from a simulation-based inference (SBI) analysis of galaxy clustering from the new SIMBIG forward modeling framework. SIMBIG leverages the predictive power of high-fidelity simulations and provides an inference framework that can extract cosmological information on small non-linear scales, inaccessible with standard analyses. In this work, we apply SIMBIG to the BOSS CMASS galaxy sample and analyze the power spectrum, P(k), to kmax=0.5h/Mpc. We construct 20,000 simulated galaxy samples using our forward model, which is based on high-resolution QUIJOTE N-body simulations and includes detailed survey realism for a more complete treatment of observational systematics. We then conduct SBI by training normalizing flows using the simulated samples and infer the posterior distribution of ΛCDM cosmological parameters: Ωm,Ωb,h,ns,σ8. We derive significant constraints on Ωm and σ8, which are consistent with previous works. Our constraints on σ8 are 27% more precise than standard analyses. This improvement is equivalent to the statistical gain expected from analyzing a galaxy sample that is 60% larger than CMASS with standard methods. It results from additional cosmological information on non-linear scales beyond the limit of current analytic models, k>0.25h/Mpc. While we focus on P in this work for validation and comparison to the literature, SIMBIG provides a framework for analyzing galaxy clustering using any summary statistic. We expect further improvements on cosmological constraints from subsequent SIMBIG analyses of summary statistics beyond P.


Comment: 9 pages, 5 figures

Subject: Astrophysics - Cosmology and Nongalactic Astrophysics


The \simbig~forward model produces simulated galaxy samples with the same survey geometry and observational systematics as the observed BOSS CMASS SGC galaxy sample. We present the 3D distribution of the galaxies from three different viewing angles. The colormap represents the redshift of the galaxies. In the top set of panels, we present the distribution of galaxies in the CMASS sample. In the bottom, we present the distribution of a simulated galaxy sample, generated from our forward model. The \simbig~galaxy samples are constructed from {\sc Quijote} $N$-body dark matter simulations using an HOD model that populates dark matter halos identified using the {\sc Rockstar} algorithm. The 3D distributions illustrate that our forward model is able to generate galaxy distributions that are difficult to statistically distinguish from observations. For more comparisons of the 3D distributions, we refer readers to \href{}{\faGlobe}.