Difference Between Half-mass Radius and Half-light Radius of Galaxies at 0.2 $<z<$ 2.5 Revealed by JWST/NIRCam Data

Abstract

Using JWST observations in CANDELS fields, we measure the half-light radius ($r_{\mathrm{e},\mathrm{light}}$) and half-mass radius ($r_{\mathrm{e},\mathrm{mass}}$) for 14,333 galaxies with stellar masses $M_{\ast }>10^9{M}_{\odot }$ at redshifts $0.2<z<2.5$. To investigate the difference between $r_{\mathrm{e},\mathrm{light}}$ and $r_{\mathrm{e},\mathrm{mass}}$, we find that $r_{\mathrm{e},\mathrm{light}}$ is larger than $r_{\mathrm{e},\mathrm{mass}}$ for both quiescent galaxies (QGs) and star-forming galaxies (SFGs). Moreover, the difference between these two radii is clearly correlated with galaxy stellar mass, $r_{\mathrm{e},\mathrm{light}}$, and the rest-frame $U-V$ color. When examining the evolution of the $r_{\mathrm{e},\mathrm{mass}}/r_{\mathrm{e},\mathrm{light}}$ ratio, we observe a significant increase for SFGs at $z>1.7$. In contrast, no clear increase is observed for QGs at $z>1$, though a slight decreasing trend is seen between $0.2<z<1.0$. By fitting a linear relationship between galaxy size and stellar mass, we find that the slope for $r_{\mathrm{e},\mathrm{light}}$ is $\sim$ 0.1 to 0.3 dex larger than that for $r_{\mathrm{e},\mathrm{mass}}$. In terms of galaxy size evolution at a fixed stellar mass, the $r_{\mathrm{e},\mathrm{mass}}$ of QGs increases by a factor of $\sim$ 3 to 5 from $z\sim 2.5$ to $z\sim 0.2$. In contrast, the $r_{\mathrm{e},\mathrm{mass}}$ of SFGs increases by a factor of approximately 2 over the same redshift range, with this growth trend closely following that of their $r_{\mathrm{e},\mathrm{light}}$. These results indicate that previous insights into galaxy evolution based on $r_{\mathrm{e},\mathrm{light}}$ remain valid when considering $r_{\mathrm{e},\mathrm{mass}}$, although the specific slopes show some variations.

arXiv comment18 pages, 14 figures, 3 tables; published in The Astrophysical Journal