No Tension: JWST Galaxies at z > 10 Consistent with Cosmological Simulations

Summary

Abstract

McCaffrey and collaborators compare galaxies observed above redshift 10 by the JWST JADES and CEERS surveys with galaxies from the Renaissance Simulations. After accounting for the additional growth expected beyond the simulations’ ending redshifts, the most massive simulated galaxies have stellar masses and star-formation rates consistent with the observations. The results show that the current JWST measurements can be explained within the standard ΛCDM model.

1. Introduction

• JWST has identified several galaxies above redshift 10 with surprisingly large stellar masses and active star formation.
• These measurements raised questions about whether galaxies could grow quickly enough within the standard ΛCDM model.
• The study uses high-resolution simulations to follow the early assembly of galaxies too small for larger cosmological simulations to resolve.

2.1 Renaissance Simulations

• Renaissance models galaxy formation in dense, average-density, and underdense regions of a ΛCDM universe.
• Its high resolution follows galaxies from stellar masses near 10⁴ solar masses to a few times 10⁷ solar masses.
• The simulations include Population III and Population II star formation, radiation, supernova feedback, chemistry, and metal enrichment.

2.2 Extrapolating Stellar Mass

• Some simulation regions end at higher redshifts than the observed galaxies, so their stellar masses are projected forward in time.
• The authors use a range of specific star-formation rates measured directly from Renaissance to estimate the possible future growth.

3.1 Most Massive Galaxies

• The most massive galaxies in the Rarepeak and Normal regions are consistent with the stellar masses measured by JADES and CEERS.
• The simulated star-formation rates are also generally consistent with the observed galaxies.
• The galaxies are rare but remain within the abundance expected in a ΛCDM universe.

3.2 Full Galaxy Population

• Renaissance follows a large population of smaller galaxies that remain below the current JWST detection limit.
• These galaxies connect smoothly with more massive galaxies from other simulations and with the JADES and CEERS observations.
• The comparison suggests that the observed galaxies are the bright end of a much larger early galaxy population.

3.3 Stellar Mass and Halo Mass

• Star formation is inefficient in small halos below the atomic-cooling threshold and is strongly affected by stellar feedback.
• Once halos reach approximately 10⁸ solar masses, atomic cooling increases their ability to form stars.
• The average star-formation efficiency rises to a few percent as halos approach 10⁹ solar masses.

4. Discussion and Conclusions

• The simulated galaxies reproduce the stellar masses and star-formation rates of the currently confirmed JADES and CEERS galaxies.
• Renaissance resolves the early stages of galaxy assembly that are missing from simulations covering larger volumes.
• The authors find no clear conflict between these JWST observations and standard ΛCDM galaxy formation.

Best Figures

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