Enhanced Sub-kpc Scale Star-formation: Results From A JWST Size Analysis of 341 Galaxies At 5<z<14

Abstract

We present a comprehensive search and analysis of high-redshift galaxies in a suite of nine public JWST extragalactic fields taken in Cycle 1, covering a total effective search area of $\sim 358\mathrm{arcmi}{\mathrm{n}}^2$. Through conservative ($8\sigma$) photometric selection, we identify 341 galaxies at $5<z<14$, with 109 having spectroscopic redshift measurements from the literature, including recent JWST NIRSpec observations. Our regression analysis reveals that the rest-frame UV size-stellar mass relation follows $R_{\mathrm{eff}}\propto M_{\ast }^{0.19\pm 0.03}$, similar to that of star-forming galaxies at $z\sim 3$, but scaled down in size by $\sim 0.7$dex. We find a much slower rate for the average size evolution over the redshift range, $R_{\mathrm{eff}}\propto (1+z{)}^{-0.4\pm 0.2}$, than that derived in the literature. A fraction ($\sim 13\%$) of our sample are marginally resolved even in the NIRCam imaging ($<100$pc), located at $>1.5\sigma$ below the derived size-mass slope. These compact sources exhibit a high star formation surface density ${\Sigma }_{\mathrm{SFR}}>10M_{\odot }\mathrm{y}{\mathrm{r}}^{-1}\mathrm{kp}{\mathrm{c}}^{-2}$, a range in which only $<0.01\%$ of the local star-forming galaxy sample is found. For those with available NIRSpec data, no evidence of ongoing supermassive black hole accretion is observed. A potential explanation for the observed high [OIII]-to-Hbeta ratios could be high shock velocities, likely originating within intense star-forming regions characterized by high ${\Sigma }_{\mathrm{SFR}}$. Lastly, we find that the rest-frame UV and optical sizes of our sample are comparable. Our results are consistent with these early galaxies building up their structures inside-out and yet to exhibit the strong color gradient seen at lower redshift.

Accepted for publication in ApJ

Cited by in corpus (1)

• Galaxy Build-up in the first 1.5 Gyr of Cosmic History: Insights from the Stellar Mass Function at $z\sim 4-9$ from JWST NIRCam Observations