Fast and realistic large-scale structure from machine-learning-augmented random field simulations

Abstract

Producing thousands of simulations of the dark matter distribution in the Universe with increasing precision is a challenging but critical task to facilitate the exploitation of current and forthcoming cosmological surveys. Many inexpensive substitutes to full $N$-body simulations have been proposed, even though they often fail to reproduce the statistics of the smaller, non-linear scales. Among these alternatives, a common approximation is represented by the lognormal distribution, which comes with its own limitations as well, while being extremely fast to compute even for high-resolution density fields. In this work, we train a generative deep learning model, mainly made of convolutional layers, to transform projected lognormal dark matter density fields to more realistic dark matter maps, as obtained from full $N$-body simulations. We detail the procedure that we follow to generate highly correlated pairs of lognormal and simulated maps, which we use as our training data, exploiting the information of the Fourier phases. We demonstrate the performance of our model comparing various statistical tests with different field resolutions, redshifts and cosmological parameters, proving its robustness and explaining its current limitations. When evaluated on 100 test maps, the augmented lognormal random fields reproduce the power spectrum up to wavenumbers of $1h{\mathrm{Mpc}}^{-1}$, and the bispectrum within 10%, and always within the error bars, of the fiducial target simulations. Finally, we describe how we plan to integrate our proposed model with existing tools to yield more accurate spherical random fields for weak lensing analysis.

16 pages, 11 figures. Matches MNRAS published version, which includes more tests with e.g. varying cosmological parameters

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• KiDS-Legacy: Covariance validation and the unified OneCovariance framework for projected large-scale structure observables
• Psi-GAN: A power-spectrum-informed generative adversarial network for the emulation of large-scale structure maps across cosmologies and redshifts
• Secondary halo bias through cosmic time II: Reconstructing halo properties using clustering information
• Deep learning approach for identification of HII regions during reionization in 21-cm observations -- III. image recovery
• Neural style transfer of weak lensing mass maps
• Generative modeling of convergence maps based on predicted one-point statistics
• Conditional variational autoencoders for cosmological model discrimination and anomaly detection in cosmic microwave background power spectra