JWST/MIRI Reveals the True Number Density of Massive Galaxies in the Early Universe

JWST/MIRI Reveals the True Number Density of Massive Galaxies in the Early Universe

Early JWST studies reporting an unexpected abundance of massive galaxies at z  ∼ 5–8 challenge galaxy formation models in the ΛCDM framework. Previous stellar mass ( M _⋆ ) estimates suffered from large uncertainties due to the lack of rest-frame near-infrared data. Using deep JWST/NIRCam and Mid-In...

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Main Authors: Tao Wang, Hanwen Sun, Luwenjia Zhou, Ke Xu, Cheng Cheng, Zhaozhou Li, Yangyao Chen, H. J. Mo, Avishai Dekel, Tiancheng Yang, Yijun Wang, Longyue Chen, Xianzhong Zheng, Zheng Cai, David Elbaz, Y.-S. Dai, J.-S. Huang
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal Letters
Subjects:
Galaxy formation
Early universe
High-redshift galaxies
Cosmology
Online Access:https://doi.org/10.3847/2041-8213/adebe7
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Summary:Early JWST studies reporting an unexpected abundance of massive galaxies at z  ∼ 5–8 challenge galaxy formation models in the ΛCDM framework. Previous stellar mass ( M _⋆ ) estimates suffered from large uncertainties due to the lack of rest-frame near-infrared data. Using deep JWST/NIRCam and Mid-Infrared Instrument (MIRI) photometry from Public Release IMaging for Extragalactic Research, we systematically analyze massive galaxies at z  ∼ 3–8, leveraging rest-frame ≳1 μ m constraints. We find MIRI is critical for robust M _⋆ measurements for massive galaxies at z  > 5: excluding MIRI overestimates M _⋆ by ∼0.4 dex on average for M _⋆  > 10 ^10 M _⊙ galaxies, with no significant effects at lower masses. This reduces number densities of M _⋆  > 10 ^10 M _⊙ (10 ^10.3 M _⊙ ) galaxies by ∼36% (55%). MIRI inclusion also reduces “Little Red Dot” (LRD) contamination in massive galaxy samples, lowering the LRD fraction from ∼32% to ∼13% at M _⋆  > 10 ^10.3 M _⊙ . Assuming pure stellar origins, LRDs exhibit M _⋆  ∼ 10 ^9–10.5 M _⊙ with MIRI constraints, rarely exceeding 10 ^10.5 M _⊙ . Within standard ΛCDM, our results indicate a moderate increase in the baryon-to-star conversion efficiency ( ϵ ) toward higher redshifts and masses at z  > 3. For the most massive z  ∼ 8 galaxies, ϵ  ∼ 0.3, compared to ϵ  ≲ 0.2 for typical galaxies at z  < 3. This result is consistent with models where high gas densities and short free-fall times suppress stellar feedback in massive high- z halos.
ISSN:2041-8205

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