Horizon Run 4 Simulation: Coupled Evolution of Galaxies and Large-scale Structures of the Universe

TL;DR

The Horizon Run 4 simulation models the coupled evolution of galaxies and large-scale cosmic structures, providing detailed data for testing cosmological theories and revealing deviations in halo mass functions and BAO features.

Contribution

This work presents a high-resolution, large-volume cosmological simulation with detailed halo merger trees and data sets for testing galaxy formation models and cosmological theories.

Findings

Halo mass function deviates from universal form with redshift evolution.

BAO feature in galaxy correlation function broadens and shifts with direction.

Less massive halos form earlier, reaching half their mass at higher redshifts.

Abstract

The Horizon Run 4 is a cosmological $N$-body simulation designed for the study of coupled evolution between galaxies and large-scale structures of the Universe, and for the test of galaxy formation models. Using $6300^3$ gravitating particles in a cubic box of $L_{\rm box} = 3150 ~h^{-1}{\rm Mpc}$, we build a dense forest of halo merger trees to trace the halo merger history with a halo mass resolution scale down to $M_s = 2.7 \times 10^{11} h^{-1}{\rm M_\odot}$. We build a set of particle and halo data, which can serve as testbeds for comparison of cosmological models and gravitational theories with observations. We find that the FoF halo mass function shows a substantial deviation from the universal form with tangible redshift evolution of amplitude and shape. At higher redshifts, the amplitude of the mass function is lower, and the functional form is shifted toward larger values of $\ln (1/\sigma)$. We also find that the baryonic acoustic oscillation feature in the two-point correlation function of mock galaxies becomes broader with a peak position moving to smaller scales and the peak amplitude decreasing for increasing directional cosine $\mu$ compared to the linear predictions. From the halo merger trees built from halo data at 75 redshifts, we measure the half-mass epoch of halos and find that less massive halos tend to reach half of their current mass at higher redshifts. Simulation outputs including snapshot data, past lightcone space data, and halo merger data are available at http://sdss.kias.re.kr/astro/Horizon-Run4/.