December
2025
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2025ApJS..281...68Y
Authors
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Yang, Lilan
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Kartaltepe, Jeyhan S.
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Franco, Maximilien
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Ding, Xuheng
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Achenbach, Mark J.
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Arango-Toro, Rafael C.
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Casey, Caitlin M.
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Drakos, Nicole E.
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Faisst, Andreas L.
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Gillman, Steven
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Gozaliasl, Ghassem
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Huertas-Company, Marc
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Jin, Shuowen
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Liu, Daizhong
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Magdis, Georgios
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Massey, Richard
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Silverman, John D.
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Tanaka, Takumi S.
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Yu, Si-Yue
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Akins, Hollis B.
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Allen, Natalie
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Ilbert, Olivier
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Koekemoer, Anton M.
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McCracken, Henry Joy
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Paquereau, Louise
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Rhodes, Jason
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Robertson, Brant E.
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Shuntov, Marko
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Toft, Sune
Abstract
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We measure galaxy sizes from 2 < z < 10 using COSMOS-Web, the largest-area JWST imaging survey to date, covering ∼0.54 deg2. We analyze the rest-frame optical (∼5000 Å) size evolution and its scaling relation with stellar mass ( Re∝M*α ) for star-forming and quiescent galaxies. For star-forming galaxies, the slope α remains approximately 0.20 at 2 < z < 8, showing no significant evolution over this redshift range. At higher redshifts, the slopes are −0.13 ± 0.15 and 0.37 ± 0.36 for 8 < z < 9 and 9 < z < 10, respectively. At fixed galaxy mass, the size evolution for star-forming galaxies follows Re ∝ (1 + z)−1.21±0.05. For quiescent galaxies, the size─mass relation is steeper with α ∼ 0.5─0.8 at 2 < z < 5, and size evolves as Re ∝ (1 + z)−0.81±0.26. We find that the size−mass relation is consistent between UV and optical at z < 8 for star-forming galaxies. However, we observe a decrease in the slope from UV to optical at z > 8, with a tentative negative slope in the optical at 8 < z < 9, suggesting a complex interplay between intrinsic galaxy properties and observational effects such as dust attenuation. We discuss the ratio between galaxies' half-light radius and underlying halos' virial radius, Rvir, and find the median value of Re/Rvir = 2.7%. The star formation rate surface density evolves as log(ΣSFR/(M⊙/yr/kpc2))= (0.20 ± 0.08)z + (−0.65 ± 0.51), and the ΣSFR─M* relation remains flat at 2 < z < 10. Lastly, we identify a threshold in stellar mass surface density log(Σe/(M⊙/kpc2))∼9.5−10 marking the transition to compact, quenched galaxies from extended, star-forming progenitors. In summary, our findings show that the extensive COSMOS-Web dataset at z > 3 provides new insights into galaxy size and related properties in the rest-frame optical.
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