Deep VLT/MUSE optical integral field spectroscopy has recently revealed an abundant population of ultra-faint galaxies (MUV≈−15; 0.01 L⋆) at z=2.9−6.7 due to their strong Lyman-α emission with no detectable continuum. The implied Lyman-α equivalent widths can be in excess of 100-200 Angstrom, challenging existing models of normal star formation and indicating extremely young ages, small stellar masses, and a very low amount of metal enrichment. We use JWST/NIRSpec's microshutter array to follow-up 45 of these galaxies (11h in G235M/F170LP and 7h in G395M/F290LP), as well as 45 lower-equivalent width Lyman-α emitters. Our spectroscopy covers the range 1.7−5.1 micron in order to target strong optical emission lines: Hα, [N II], [O III], and Hβ. Individual measurements as well as stacks reveal line ratios consistent with a metal poor nature (2−40% Z⊙, depending on the calibration). The galaxies with the highest equivalent widths of Lyman-α, in excess of 90 Angstrom, have lower [N II]/Hα (1.9-σ) and [O III]/Hβ (2.2-σ) ratios than those with lower equivalent widths, implying lower gas-phase metallicities at a combined significance of 2.4-σ. This implies a selection based on Lyman-α equivalent width is an efficient technique for identifying younger, less chemically enriched systems.
@article{arxiv.2304.08511,
title = {JWST/NIRSpec Measurements of Extremely Low Metallicities in High Equivalent Width Lyman-$\alpha$ Emitters},
author = {Michael V. Maseda and Zach Lewis and Jorryt Matthee and Joseph F. Hennawi and Leindert Boogaard and Anna Feltre and Themiya Nanayakkara and Roland Bacon and Amy Barger and Jarle Brinchmann and Marijn Franx and Takuya Hashimoto and Hanae Inami and Haruka Kusakabe and Floriane Leclercq and Lucie Rowland and Anthony J. Taylor and Christy Tremonti and Tanya Urrutia and Joop Schaye and Charlotte Simmonds and Eloïse Vitte},
journal= {arXiv preprint arXiv:2304.08511},
year = {2023}
}