COSMOS-Web: Galaxy Size and Surface Brightness Evolution at Rest Frame 1.22 μm Since z = 3

July 2026 • 2026ApJ..1005L..13Y

Authors • Yu, Si-Yue • Faisst, Andreas L. • Fang, Taotao • Toni, Greta • Moscardini, Lauro • Franco, Maximilien • Samir, Rasha M. • Hirschmann, Michaela • Zhang, Xiaoxia • Leroy, Gavin

Abstract • We present the evolution of galaxy size and surface brightness in the rest-frame J band (1.22 μm), tracing the stellar mass distribution, over 0.5 ≤ z ≤ 3, using a sample of 15,420 galaxies with stellar masses M_⋆ = 10¹⁰─10^11.5M_⊙ from the JWST COSMOS-Web survey. The rest-frame J-band effective radius (R_e,J) is obtained from previous measurements and mapped from the available JWST/NIRCam filters, while the surface brightness (μ_J) is corrected for dust extinction and cosmological dimming. At a characteristic mass of M_⋆ = 5 × 10¹⁰M_⊙, star-forming galaxies (SFGs) exhibit a size evolution of R_e,J ∝ (1 + z)^β with β = −0.92 ± 0.04, falling between previously reported shallower and steeper measurements. Quiescent galaxies evolve more rapidly, with β = −1.34 ± 0.05, consistent with earlier studies. Among SFGs, lower-mass systems (10¹⁰─10^10.5M_⊙) show slower (β = −0.66 ± 0.02) size evolution compared to their higher-mass counterparts. Furthermore, the surface brightness brightens toward higher redshifts, scaling as μJ∝−2.5log(1+z)γ . We find γ = 3.07 ± 0.08 for SFGs and γ = 3.70 ± 0.08 for quiescent galaxies. We also find that massive SFGs (M_⋆ > 10^10.5 M_⊙) exhibit similar μ_J values at fixed redshift, independent of mass. Finally, we demonstrate that the observed surface brightness evolution is driven by the combined evolution of galaxy luminosity and size.

Links

• ELECTR https://doi.org/10.3847/2041-8213/ae77f8
• PREPRINT http://arxiv.org/abs/2605.31415