James Webb Space Telescope Feed Post

JADES | Enhanced Sub-kpc Scale Star-formation: Results From A JWST Size Analysis of 339 Galaxies At 5 < z < 14

Sources that are classified as compact. (lef t): original image, in the UV band where the size is measured. (middle): galfit single Sersic model image (with Sersic index fixed to 1). (right): residual image. Those with spectroscopic redshift measurements are color-coded its redshift label in cyan. 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 ~358arcmin2. Through conservative (8s) photometric selection, we identify 339 galaxies at 51.5s below the derived size-mass slope. These compact sources exhibit a high star formation surface density SSFR>10M?yr-1kpc-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 SSFR. 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.