## Scientific Purpose

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 $L_\mathrm{box} = 3150 h^{-1}\mathrm{Mpc}$, we build a dense forest of halo merger trees to trace the halo merger history with a halo mass resolution scale down to $M_\text{s} = 2.7 \times 10^{11} h^{-1} M_\odot$. 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 μ 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.

## Authors

- Juhan Kim at CAC of Korea Institute for Advanced Study (KIAS; email contact: kjhan _at_ kias.re.kr)
- Changbom Park at KIAS
- Benjamin L'Huillier at KIAS (corresponding author: lhuillier _at_ kias.re.kr)
- Sungwook E. Hong at KIAS

## Cosmological model of the Horizon Runs (HR's)

All the HR's share the same cosmology.

### Cosmological parameters of the HR's

Cosmological model | $\Omega_{m,0}$ | $\Omega_{b,0}$ | $\Omega_{\Lambda,0}$ | $n_\mathrm{s}$ | $H_0$ (km/s/Mpc) | $\sigma_8$ |
---|---|---|---|---|---|---|

$\Lambda$CDM WMAP5 | 0.26 | 0.044 | 0.74 | 0.96 | 72 | 1/1.26 |

### Simulations specifics

Simulations Name | HR1 | HR2 | HR3 | HR4 |
---|---|---|---|---|

Box Size ($h^{-1}\mathrm{Mpc}$) | 6592 | 7200 | 10815 | 3150 |

Number of CDM particles | $4120^3$ | $6000^3$ | $7210^3$ | $6300^3$ |

Starting redshift | 23 | 32 | 27 | 100 |

Initial power spectrum generator | Eisenstein & Hu (1998) | CAMB Source | CAMB Source | CAMB Source |

Initial displacement | Zel'dovich | Zel'dovich | Zel'dovich | 2LPT |

## Outputs from the simulation

The data are available upon request. Please contact directly Juhan Kim (kjhan _at_ kias.re.kr)

- Snapshot data at $z= 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 1,$ and $4$
- All-sky past lightcone data out to $z=1.5$
- Merger trees of FoF halos from $z = 16$ to $0$, with their gravitationally most bound member particles