COSMOS-Web: Unraveling the Evolution of Galaxy Size and Related Properties at $2<z<10$

Lilan Yang; Jeyhan S. Kartaltepe; Maximilien Franco; Xuheng Ding; Mark J. Achenbach; Rafael C. Arango-Toro; Caitlin M. Casey; Nicole E. Drakos; Andreas L. Faisst; Steven Gillman; Ghassem Gozaliasl; Marc Huertas-Company; Shuowen Jin; Daizhong Liu; Georgios Magdis; Richard Massey; John D. Silverman; Takumi S. Tanaka; Si-Yue Yu; Hollis B. Akins; Natalie Allen; Olivier Ilbert; Anton M. Koekemoer; Henry Joy McCracken; Louise Paquereau; Jason Rhodes; Brant E. Robertson; Marko Shuntov; Sune Toft

arXiv · 2504.07185

COSMOS-Web: Unraveling the Evolution of Galaxy Size and Related Properties at $2<z<10$

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Abstract

We measure galaxy sizes from $2 < z < 10$ using COSMOS-Web, the largest-area JWST imaging survey to date, covering $\sim$0.54 deg$^2$. We analyze the rest-frame optical (~5000A) size evolution and its scaling relation with stellar mass ($R_e\propto M_*^\alpha$) for star-forming and quiescent galaxies. For star-forming galaxies, the slope $\alpha$ remains approximately 0.20 at $2 < z < 8$, showing no significant evolution over this redshift range. At higher redshifts, the slopes are $-0.13 \pm 0.15$ and $0.37 \pm 0.36$ for $8 < z < 9$ and $9 < z < 10$, respectively. At fixed galaxy mass, the size evolution for star-forming galaxies follows $R_e \propto (1+z)^{-\beta}$, with $\beta = 1.21 \pm 0.05$. For quiescent galaxies, the slope is steeper $\alpha\sim 0.5$-$0.8$ at $2 < z < 5$, and $\beta=0.81\pm0.26$. 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, $R_{vir}$, and find the median value of $R_e/R_{vir}=2.7\%$. The star formation rate surface density evolves as $\log\Sigma_\text{SFR} = (0.20\pm0.08)\,z+(-0.65\pm0.51)$, and the $\Sigma_\text{SFR}$-$M_*$ relation remains flat at $2 3$ provides new insights into galaxy size and related properties in the rest-frame optical.

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Lilan Yang, Jeyhan S. Kartaltepe, Maximilien Franco, Xuheng Ding, Mark J. Achenbach, Rafael C. Arango-Toro, Caitlin M. Casey, Nicole E. Drakos, Andreas L. Faisst, Steven Gillman, Ghassem Gozaliasl, Marc Huertas-Company, Shuowen Jin, Daizhong Liu, Georgios Magdis, Richard Massey, John D. Silverman, Takumi S. Tanaka, Si-Yue Yu, Hollis B. Akins, Natalie Allen, Olivier Ilbert, Anton M. Koekemoer, Henry Joy McCracken, Louise Paquereau, Jason Rhodes, Brant E. Robertson, Marko Shuntov, Sune Toft. 2025-04-09. COSMOS-Web: Unraveling the Evolution of Galaxy Size and Related Properties at $2<z<10$. https://arxiv.org/abs/2504.07185

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