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

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_{\ast }^{\hat{I}}\pm$) for star-forming and quiescent galaxies. For star-forming galaxies, the slope $\hat{I}\pm$ 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 $R_e\propto (1+z{)}^{-{\hat{I}}^2}$, with ${\hat{I}}^2=1.21\pm 0.05$. For quiescent galaxies, the slope is steeper $\hat{I}\pm \sim 0.5$-$0.8$ at $2<z<5$, and ${\hat{I}}^2=0.81\pm 0.26$. 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, $R_{vir}$, and find the median value of $R_e/R_{vir}=2.7\%$. The star formation rate surface density evolves as $\log \hat{I}{\pounds }_{\text{SFR}}=(0.20\pm 0.08)z+(-0.65\pm 0.51)$, and the $\hat{I}{\pounds }_{\text{SFR}}$-$M_{\ast }$ relation remains flat at $2<z<10$. Lastly, we identify a threshold in stellar mass surface density $\log \hat{I}{\pounds }_e\sim 9.5$-$10M_{\odot }/kp{c}^2$ 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.

23 pages, 13 figures, submitted