A Close Look at Ly$\alpha$ Emitters with JWST/NIRCam at $z\approx3.1$

TL;DR

This study uses JWST/NIRCam observations to analyze 10 Ly$ extalpha$ emitters at $z oughly3.1$, revealing their morphology, strong emission lines, and starbursting nature, which challenges existing scaling relations for low-mass galaxies.

Contribution

First detailed JWST/NIRCam analysis of spectroscopically confirmed Ly$ extalpha$ emitters at $z oughly3.1$, highlighting their unique starbursting dwarf galaxy properties.

Findings

All LAEs detected across NIRCam bands with strong [O III]+H$eta$ emission.

Three LAEs are resolved into pairs, three show asymmetric structures.

Sample exhibits very small sizes, low stellar mass, and very young ages, deviating from typical $z oughly3$ scaling relations.

Abstract

We study 10 spectroscopically confirmed Ly$\alpha$ emitters (LAEs) at $z\approx3.1$ 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 2200\AA--1.2$\mathrm{\mu m}$. 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]+H$\beta$ emission lines (${\rm EW_{rest}}=740$--$6500\,$\AA). The median effective radii, stellar mass, and UV slope of our sample are 0.36$\,$kpc, $3.8\times10^7\,M_\odot$, and --2.48, respectively. The average burst age, estimated by stellar mass over star formation rate, is $<40\,$Myr. These measurements reveal an intriguing starbursting dwarf galaxy population lying off the extrapolations of the $z \sim 3$ scaling relations to the low-mass end: $\sim 0.7$ dex above the star-forming main sequence, $\sim 0.35$ 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.