[Paper Review] Confirmation of the standard cosmological model from red massive galaxies $\sim600$ Myr after the Big Bang

Francisco Prada, Peter Behroozi+3 more|arXiv (Cornell University)|Apr 24, 2023

Galaxies: Formation, Evolution, Phenomena12 citations

TL;DR

This note argues that standard cosmology, via the Uchuu-UM galaxy formation model, explains JWST/HST results and UV luminosity functions at z~8–10 and challenges claims of anomalously massive red galaxies reported by Labbé et al. by attributing high stellar masses to potential systematics and dust effects.

ABSTRACT

In their recent study, Labbé et al. used multi-band infrared images captured by the James Webb Space Telescope (JWST) to discover a population of red massive galaxies that formed approximately 600 million years after the Big Bang. The authors reported an extraordinarily large density of these galaxies, with stellar masses exceeding $10^{10}$ solar masses, which, if confirmed, challenges the standard cosmological model as suggested by recent studies. However, this conclusion is disputed. We contend that during the early epochs of the universe the stellar mass-to-light ratio could not have reached the values reported by Labbé et al. A model of galaxy formation based on standard cosmology provides support for this hypothesis, predicting the formation of massive galaxies with higher ultraviolet (UV) luminosity, which produce several hundred solar masses of stars per year and containing significant dust. These forecasts are consistent with the abundance of JWST/HST galaxies selected photometrically in the rest-frame UV wavelengths and with the properties of the recent spectroscopically-confirmed JWST/HST galaxies formed during that era. Discrepancies with Labbé et al. may arise from overestimation of the stellar masses, systematic uncertainties, absence of JWST/MIRI data, heavy dust extinction affecting UV luminosities, or misidentification of faint red AGN galaxies at closer redshifts. The current JWST/HST results, combined with a realistic galaxy formation model, provide strong confirmation of the standard cosmology.

Motivation & Objective

• Motivate that the high stellar-mass densities reported at z~8 by Labbé et al. can be reconciled with standard cosmology.
• Demonstrate that an empirical galaxy formation model (Uchuu-UM) reproduces observed UV luminosity functions and SFR densities.
• Show that discrepancies with Labbé et al. may arise from mass estimation systematics, dust extinction, or misidentification of red AGN.
• Validate predictions using UniverseMachine-based galaxy catalogs linked to Uchuu N-body simulations across z=0–20.

Proposed method

• Use Uchuu-UM galaxy catalogs generated with UniverseMachine applied to Shin-Uchuu and Uchuu1000-PL18 simulations.
• Compare model UV luminosity functions to JWST and HST measurements at z=8, 9, 10 (rest-frame UV).
• Compute evolution of cosmic UV luminosity and SFR density for galaxies down to M_UV = -17 and compare to JWST data.
• Examine stellar-mass density evolution and contrast Uchuu-UM predictions with Labbé et al.’s z~8 masses above 1e10 M_sun.
• Assess potential systematics: JWST/MIRI data impact on mass estimates and dust extinction effects.

Experimental results

Research questions

• RQ1 Do Uchuu-UM predictions reproduce the observed rest-frame UV luminosity functions at z≈8–10?
• RQ2 Is the high stellar-mass density reported by Labbé et al. at z≈8 tenable within standard cosmology when accounting for dust and data-systematics?
• RQ3 How does the cosmic UV luminosity/SFR density evolution predicted by Uchuu-UM compare with JWST measurements from z≈7–14?
• RQ4 What are the implications of potential systematic effects (e.g., MIRI data, dust extinction, AGN contamination) on inferred high-z stellar masses?

Key findings

• Uchuu-UM accurately reproduces JWST and HST rest-frame UV luminosity functions across z=8–10, both with and without internal dust extinction.
• The model's UV/SFR density evolution is in good agreement with JWST observations over z≈7–14.
• Spectroscopically-confirmed JWST/HST galaxies at z≈8.5 are well explained by Uchuu-UM in terms of SFR–stellar mass and stellar-mass–UV luminosity relations.
• Labbé et al.’s red massive galaxies show ~50x higher stellar mass for a given UV luminosity than Uchuu-UM would predict, suggesting possible mass estimation systematics or extreme dust/extinction scenarios.
• If Labbé et al.’s masses are accepted, the results would imply extreme efficiency or rare events, not required by current JWST data when using a realistic model.
• Overall, the combination of JWST/HST results and Uchuu-UM supports the standard cosmological model rather than challenging it.