Reproducing Abell 2744 with the HyperMillennium Simulation

TL;DR

The paper introduces the Hyper Millennium (HM) simulation, an ultra-large dark matter N-body run designed to support next-generation galaxy surveys. It uses a PM-FMM gravity code (PhotoNs-3.7) with GPU acceleration and a mixed-precision strategy, combined with the L-GALAXIES semi-analytic model to populate galaxies and produce JWST-like mock catalogs. Focusing on Abell 2744, the authors select analogues via Procrustes morphometric analysis and mass-ratio criteria, and generate mock projected mass maps and JWST images to compare with UNCOVER lensing reconstructions. After accounting for observational field biases that favor high galaxy surface density, the pixel-based light–mass statistics of the HM analogues align remarkably well with A2744, thereby validating ΛCDM in the extreme cluster regime and demonstrating HM’s utility for realistic high-redshift mock catalogs across a 45 ${ m Gpc^3}$ volume.

Abstract

We present the Hyper Millennium (HM) simulation, an extremely large cosmological simulation designed to support next-generation galaxy surveys. The simulation follows 4.2 trillion dark matter particles in a comoving box of $2.5\ h^{-1}{\rm Gpc}$, with a mass resolution of $3.2 \times 10^8\, {\rm M}_{\odot}$ and a force resolution of $3.0\ h^{-1}{\rm kpc}$. Its combination of scale and resolution is ideal for studying large-scale structures and rare cosmic objects. In this first paper of the HM project, we explore whether the massive galaxy cluster Abell 2744 (A2744) can be reproduced in detail in the simulation. Pixel-based statistics of galaxy number density $N_{\rm gal}$, luminosity density $L_{\rm gal}$, and projected mass density $κ$ show excellent agreement between A2744 and its analogues down to $\sim 50\ {\rm kpc}$, once field-selection biases toward high galaxy surface density are accounted for. This concordance, achieved in one of the most extreme known galaxy environments, is a validation of the underlying $Λ{\rm CDM}$ model in the extreme regime of A2744 and showcases the robustness and accuracy of the HM simulation, which is capable of producing galaxy and mass catalogues of comparable quality out to high redshift across its full comoving volume of $45$ ${\rm Gpc^3}$.

Figures (11)

• Figure 1: Dark matter density slice from the HM simulation at the present epoch ($z = 0.0$). The upper-left panel displays the full simulation box with a side length of 2.5 $h^{-1}$ Gpc. The subsequent panels, arranged counterclockwise, progressively zoom in on a massive dark halo across five levels, from the large-scale structure (625 $h^{-1}$ Mpc) down to sub-halos within the inner regions of dark halos (5 $h^{-1}$ Mpc).
• Figure 2: The power spectrum evolution from the initial redshift ($z = 127$) to the present day ($z = 0$). The solid curves represent the reference predictions from CAMB with HMCode 2016MNRAS.459.1468M. The lower panel shows the ratio of the simulation measurements to the predictions, highlighting any deviations.
• Figure 3: The FOF halo mass functions measured at seven redshifts, from $z = 20.4$ to $z = 0$. The minimum halo, containing 20 particles, corresponds to a mass of $\sim 6.5 \times 10^{9}~h^{-1}\mathrm{M}_\odot$. The solid curves represent the predictions from the fitting model of 2007MNRAS.374....2R. The bottom panel shows the ratio as a function of halo mass, comparing the simulation results with the model predictions.
• Figure 4: A2744 analogue clusters selected from the HM simulation as they would appear at a redshift of $z = 0.308$. A composite-colour image with a field coverage of $12'.5 \times 12'.5$ for each cluster is shown, using the F444W filter for red, F277W for green, and F115W for blue. The yellow contours represent the projected mass distribution, smoothed here with a Gaussian kernel of $\sigma=2^{\prime\prime}$, mimicking the lensing convergence.
• Figure 5: The luminosity function (LF) per unit projected mass for A2744 galaxies within the FOV analysed by Cha_Etal_2024. Filled black dots connected with solid lines indicate the results when all "non-background" galaxies are used, while the green points and lines indicate the result after removing all galaxies with a spectroscopic or photometric redshift inconsistent with $z_{\rm cluster}=0.308$. The pink-shaded regions mark the area spanned by the projected, mass-normalised LFs of our nine simulated analogues of A2744.