James Webb Space Telescope Feed Post

A Close Look at Lya Emitters with JWST/NIRCam at z~3.1

A false-color image zooming in on the source UDS-154. The RGB color composite combines F115W (blue), F200W (green) and F356W (red), matching the real color in restframe. Angular scales are indicated both on the original and on the zoomed-in frame. Abstract: We study 10 spectroscopically confirmed Lya emitters (LAEs) at z˜3.1 in the UDS field, covered by JWST/NIRCam in the PRIMER program. All LAEs are detected in all NIRCam bands from F090W to F444W, corresponding to restframe 2200Å--1.2µm. Based on morphological analysis of the F200W images, three out of the 10 targets are resolved into pair-like systems with separations of <0.9'', and another three show asymmetric structures. We then construct the spectral energy distributions (SEDs) of these LAEs. All sources, including the pairs, show similar SED shapes, with a prominent flux excess in the F200W band, corresponding to extremely strong [O III]+Hß emission lines (EWrest=740--6500Å). The median effective radii, stellar mass, and UV slope of our sample are 0.36kpc, 3.8×107M?, and --2.48, respectively. The average burst age, estimated by stellar mass over star formation rate, is <40Myr. These measurements reveal an intriguing starbursting dwarf galaxy population lying off the extrapolations of the z~3 scaling relations to the low-mass end: ~0.7 dex above the star-forming main sequence, ~0.35 dex below the mass--size relation, and bluer in the UV slope than typical high-z galaxies at similar UV luminosities. We speculate that these numbers may require a larger main sequence scatter or tail in the dwarf galaxy regime towards the starburst outliers.