Showing papers by "Anatoly Klypin published in 2021"

The mass function dependence on the dynamical state of dark matter haloes

Abstract: Context. Galaxy clusters are luminous tracers of the most massive dark matter haloes in the Universe. To use them as a cosmological probe, a detailed description of the properties of dark matter haloes is required.Aims. We characterize how the dynamical state of haloes impacts the dark matter halo mass function at the high-mass end (i.e., for haloes hosting clusters of galaxies).Methods. We used the dark matter-only MultiDark suite of simulations and the high-mass objects M > 2.7 × 1013 M ⊙ h −1 therein. We measured the mean relations of concentration, offset, and spin as a function of dark matter halo mass and redshift. We investigated the distributions around the mean relations. We measured the dark matter halo mass function as a function of offset, spin, and redshift. We formulated a generalized mass function framework that accounts for the dynamical state of the dark matter haloes.Results. We confirm the recent discovery of the concentration upturn at high masses and provide a model that predicts the concentration for different values of mass and redshift with one single equation. We model the distributions around the mean values of concentration, offset, and spin with modified Schechter functions. We find that the concentration of low-mass haloes shows a faster redshift evolution compared to high-mass haloes, especially in the high-concentration regime. We find that the offset parameter is systematically smaller at low redshift, in agreement with the relaxation of structures at recent times. The peak of its distribution shifts by a factor of ∼1.5 from z = 1.4 to z = 0. The individual models are combined into a comprehensive mass function model, which predicts the mass function as a function of spin and offset. Our model recovers the fiducial mass function with ∼3% accuracy at redshift 0 and accounts for redshift evolution up to z ∼ 1.5.Results. This new approach accounts for the dynamical state of the halo when measuring the halo mass function. It offers a connection with dynamical selection effects in galaxy cluster observations. This is key toward precision cosmology using cluster counts as a probe.

Building a digital twin of a luminous red galaxy spectroscopic survey: galaxy properties and clustering covariance

Abstract: CH-A acknowledges support from the Mexican National Council of Science and Technology (CONACYT) through grant No. 286513/438352 and from the Excellence Cluster ORIGINS which is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy-EXC-2094-390783311. FP and AK thank the support of the Spanish Ministry of Science funding grant PGC2018-101931-B-I00. FP gratefully acknowledges the ICC at Durham for their warm hospitality and support during my summer visit of 2018, where this work was initiated. This work used the DiRAC@Durham facility managed by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk).The equipment was funded by BEIS capital funding via STFC capital grants ST/K00042X/1, ST/P002293/1, ST/R002371/1, and ST/S002502/1, Durham University and STFC operations grant ST/R000832/1. DiRAC is part of the National e-Infrastructure. We thank New Mexico State University (USA) and Instituto de Astrofisica de Andalucia CSIC (Spain) for hosting the Skies & Universes site (www.skiesanduniverses.org) for cosmological simulation products.

Fast full N-body simulations of generic modified gravity: conformal coupling models

Abstract: We present MG-GLAM, a code developed for the very fast production of full $N$-body cosmological simulations in modified gravity (MG) models. We describe the implementation, numerical tests and first results of a large suite of cosmological simulations for three classes of MG models with conformal coupling terms: the $f(R)$ gravity, symmetron and coupled quintessence models. Derived from the parallel particle-mesh code GLAM, MG-GLAM incorporates an efficient multigrid relaxation technique to solve the characteristic nonlinear partial differential equations of these models. For $f(R)$ gravity, we have included new variants to diversify the model behaviour, and we have tailored the relaxation algorithms to these to maintain high computational efficiency. In a companion paper, we describe versions of this code developed for derivative coupling MG models, including the Vainshtein- and K-mouflage-type models. MG-GLAM can model the prototypes for most MG models of interest, and is broad and versatile. The code is highly optimised, with a tremendous speedup of a factor of more than a hundred compared with earlier $N$-body codes, while still giving accurate predictions of the matter power spectrum and dark matter halo abundance. MG-GLAM is ideal for the generation of large numbers of MG simulations that can be used in the construction of mock galaxy catalogues and the production of accurate emulators for ongoing and future galaxy surveys.

Fast full $N$-body simulations of generic modified gravity: derivative coupling models

Abstract: We present MG-GLAM, a code developed for the very fast production of full $N$-body cosmological simulations in modified gravity (MG) models. We describe the implementation, numerical tests and first results of a large suite of cosmological simulations for two broad classes of MG models with derivative coupling terms -- the Vainshtein- and Kmouflage-type models -- which respectively features the Vainshtein and Kmouflage screening mechanism. Derived from the parallel particle-mesh code GLAM, MG-GLAM incorporates an efficient multigrid relaxation technique to solve the characteristic nonlinear partial differential equations of these models. For Kmouflage, we have proposed a new algorithm for the relaxation solver, and run the first simulations of the model to understand its cosmological behaviour. In a companion paper, we describe versions of this code developed for conformally-coupled MG models, including several variants of $f(R)$ gravity, the symmetron model and coupled quintessence. Altogether, MG-GLAM has so far implemented the prototypes for most MG models of interest, and is broad and versatile. The code is highly optimised, with a tremendous (over two orders of magnitude) speedup when comparing its running time with earlier $N$-body codes, while still giving accurate predictions of the matter power spectrum and dark matter halo abundance. MG-GLAM is ideal for the generation of large numbers of MG simulations that can be used in the construction of mock galaxy catalogues and accurate emulators for ongoing and future galaxy surveys.

Evolution of skewness and kurtosis of cosmic density fields

Abstract: Aims. We investigate the evolution of the one-point probability distribution function (PDF) of the dark matter density field and the evolution of its moments for fluctuations that are Gaussian in the linear regime.Methods. We performed numerical simulations of the evolution of the cosmic web for the conventional ΛCDM model. The simulations covered a wide range of box sizes L = 256 − 4000 h −1 Mpc, mass, and force resolutions, and epochs from very early moments z = 30 to the present moment z = 0. We calculated density fields with various smoothing lengths to determine the dependence of the density field on the smoothing scale. We calculated the PDF and its moments variance, skewness, and kurtosis. We determined the dependence of these parameters on the evolutionary epoch z , on the smoothing length R t , and on the rms deviation of the density field σ using a cubic-cell and top-hat smoothing with kernels 0.4 h −1 Mpc ≤ R t ≤ 32 h −1 Mpc.Results. We focus on the third (skewness S ) and fourth (kurtosis K ) moments of the distribution functions: their dependence on the smoothing scale R t , the amplitude of the fluctuations σ , and the redshift z . Moments S and K , calculated for density fields at different cosmic epochs and smoothed with various scales, characterise the evolution of different structures of the web. Moments calculated with small-scale smoothing (R t ≈ (1 − 4) h −1 Mpc) characterise the evolution of the web on cluster-type scales. Moments found with strong smoothing (R t ≳ (5 − 15) h −1 Mpc) describe the evolution of the web on supercluster scales. During the evolution, the reduced skewness S 3 = S /σ and reduced kurtosis S 4 = K /σ 2 present a complex behaviour: at a fixed redshift, curves of S 3 (σ ) and S 4 (σ ) steeply increase with σ at σ ≲ 1 and then flatten out and become constant at σ ≳ 2. When we fixed the smoothing scale R t , the curves at large σ started to gradually decline after reaching the maximum at σ ≈ 2. We provide accurate fits for the evolution of S 3, 4 (σ , z ). Skewness and kurtosis approach constant levels at early epochs S 3 (σ )≈3 and S 4 (σ )≈15.Conclusions. Most of the statistics of dark matter clustering (e.g. halo mass function or concentration-mass relation) are nearly universal: they mostly depend on the σ with a relatively modest correction to apparent dependence on the redshift. We find just the opposite for skewness and kurtosis: the dependence of the moments on the evolutionary epoch z and smoothing length R t is very different. Together, they uniquely determine the evolution of S 3, 4 (σ ). The evolution of S 3 and S 4 cannot be described by current theoretical approximations. The often used lognormal distribution function for the PDF fails to even qualitatively explain the shape and evolution of S 3 and S 4 .