JWST/NIRSpec Measurements of Extremely Low Metallicities in High Equivalent Width Ly Emitters

Deep Very Large Telescope/MUSE optical integral field spectroscopy has recently revealed an abundant population of ultra-faint galaxies (M-UV approximate to -15; 0.01 L-star) at z = 2.9-6.7 due to their strong Ly alpha emission with no detectable continuum. The implied Ly alpha 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 (11 hr in G235M/F170LP and 7 hr in G395M/F290LP), as well as 45 lower-equivalent width Ly alpha emitters. Our spectroscopy covers the range 1.7-5.1 micron in order to target strong optical emission lines: H alpha, [O III], H beta, and [N II]. Individual measurements as well as stacks reveal line ratios consistent with a metal-poor nature (2%-40% Z(circle dot), depending on the calibration). The galaxies with the highest equivalent widths of Ly alpha, in excess of 90 angstrom, have lower [N II]/H alpha (1.9 sigma) and [O III]/H beta (2.2 sigma) ratios than those with lower equivalent widths, implying lower gas-phase metallicities at a combined significance of 2.4 sigma. This implies a selection based on Ly alpha equivalent width is an efficient technique for identifying younger, less chemically enriched systems.