The Horizon Run 5 Cosmological Hydrodynamic Simulation: Probing Galaxy Formation from Kilo- to Giga-parsec Scales (2006.01039v3)

Abstract: Horizon Run 5 (HR5) is a cosmological hydrodynamical simulation which captures the properties of the Universe on a Gpc scale while achieving a resolution of 1kpc. Inside the simulation box we zoom-in on a high-resolution cuboid region with a volume of $1049\times119\times127\,{\rm cMpc}^3$.The sub-grid physics chosen to model galaxy formation includes radiative heating/cooling, UV background, star formation, supernova feedback, chemical evolution tracking the enrichment of oxygen and iron, the growth of supermassive black holes and feedback from active galactic nuclei (AGN) in the form of a dual jet-heating mode. For this simulation we implemented a hybrid MPI-OMP version of RAMSES, specifically targeted for modern many-core many thread parallel architectures. In addition to the traditional simulation snapshots, light-cone data was generated on the fly. For the post-processing, we extended the Friends-of-Friend (FoF) algorithm and developed a new galaxy finder PGalF to analyse the outputs of HR5. The simulation successfully reproduces observations, such as the cosmic star formation history and connectivity of galaxy distribution, We identify cosmological structures at a wide range of scales, from filaments with a length of several cMpc, to voids with a radius of ~100 cMpc. The simulation also indicates that hydrodynamical effects on small scales impact galaxy clustering up to very large scales near and beyond the baryonic acoustic oscillation (BAO) scale. Hence, caution should be taken when using that scale as a cosmic standard ruler: one needs to carefully understand the corresponding biases. The simulation is expected to be an invaluable asset for the interpretation of upcoming deep surveys of the Universe.

• The paper introduces HR5, a comprehensive simulation that integrates multi-scale hydrodynamics and subgrid physics to model galaxy formation accurately.
• The simulation employs a hybrid MPI-OpenMP RAMSES code, resolving structures from 1 kpc up to 1049 Mpc to validate key observational phenomena.
• The study warns of potential BAO measurement biases and provides a robust framework for interpreting upcoming deep cosmological surveys.

Examination of the Horizon Run 5 Cosmological Hydrodynamical Simulation

The paper presented by Lee et al. details the Horizon Run 5 (HR5) simulation, a comprehensive cosmological hydrodynamical simulation that investigates universe formation dynamics from kiloparsec to gigaparsec scales, extending our understanding of both galactic and cosmic web formation. By employing a massive simulation box with 1049 Mpc on a side and a resolution reaching down to 1 kpc, the research addresses the complexities of large-scale structures while capturing small-scale galaxy formation physics.

Simulation Design and Subgrid Physics

HR5 implements a hybrid MPI-OpenMP version of the RAMSES code to efficiently manage computational resources and accurately model the universe's evolution. This setup leverages modern multi-core systems, a fundamental step for running extensive simulations. The sub-grid physics encompass a variety of processes essential for galaxy formation: radiative heating/cooling, reionization, star formation, supernova feedback, chemical evolution, and growth and feedback from supermassive black holes (SMBH). The AGN feedback uses a dual jet-heating mode, which addresses different states of black hole activity, contributing to realistic modeling of galactic center activities.

Outcomes and Validation

The simulation replicates numerous observational results like the cosmic star formation history and stellar mass functions. Significantly, the paper emphasizes that the inclusion of hydrodynamical effects, particularly on small scales, influences galaxy clustering at scales comparable to baryonic acoustic oscillations (BAO). Consequently, using the BAO scale as a consistent cosmic standard ruler warrants caution as biases might occur.

Galaxy and Structure Analysis

A novel aspect lies in not only focusing on large-scale structures but also examining the detailed formation and evolution of galaxies, including dwarf systems, within a self-consistent cosmological framework. The simulation demonstrates significant variance from pure N-body simulations in terms of small-scale structures, likely due to hydrodynamical factors and differences in simulation methodologies. The research incorporates a robust galaxy finder to analyze the galaxies formed in the simulation efficiently.

Implications for Observational Cosmology and Computational Techniques

From a practical standpoint, HR5 aids in interpreting forthcoming deep surveys of the universe, providing a comprehensive simulation-based context to compare observational data. The insight into bias formation on various scales aids in addressing potential discrepancies between simulated and observed cosmic features.

Theoretically, HR5's capabilities point to the necessity and value of incorporating multi-scale hydrodynamics in simulations to bridge the gap between small galactic scales and large cosmic web structures. It underscores the importance of accurate sub-grid physics modeling in attaining reliable simulation outcomes which align closely with empirical data.

Future research directions should explore the astrophysical processes at both ends of the scale spectrum, particularly focusing on refining sub-grid feedback models and achieving higher resolutions computationally practicable.

Conclusion

The HR5 simulation serves as an extensive dataset that integrates a wide array of physical processes needed to simulate galaxy and cosmic web evolution accurately. Its results emphasize the delicate interplay between hydrodynamics, stellar processes, and large-scale cosmic structure formation, offering a critical tool for the theoretical and observational cosmology communities to explore diverse aspects of universe evolution.