JWST/NIRSpec Measurements of Extremely Low Metallicities in High Equivalent Width Lyα Emitters
Feltre, Anna; Bacon, Roland; Inami, Hanae; Brinchmann, Jarle; Maseda, Michael V.; Hennawi, Joseph F.; Franx, Marijn; Nanayakkara, Themiya; Hashimoto, Takuya; Boogaard, Leindert; Simmonds, Charlotte; Leclercq, Floriane; Schaye, Joop; Kusakabe, Haruka; Matthee, Jorryt; Urrutia, Tanya; Lewis, Zach; Barger, Amy; Rowland, Lucie; Taylor, Anthony J.; Tremonti, Christy; Vitte, Eloïse
United States, Switzerland, Netherlands, Germany, Italy, Australia, France, Portugal, Japan, United Kingdom, Chile
Abstract
Deep Very Large Telescope/MUSE optical integral field spectroscopy has recently revealed an abundant population of ultra-faint galaxies (M UV ≈ -15; 0.01 L ⋆) at z = 2.9-6.7 due to their strong Lyα emission with no detectable continuum. The implied Lyα equivalent widths can be in excess of 100-200 Å, 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 Lyα emitters. Our spectroscopy covers the range 1.7-5.1 micron in order to target strong optical emission lines: Hα, [O III], Hβ, and [N II]. 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 Lyα, in excess of 90 Å, have lower [N II]/Hα (1.9σ) and [O III]/Hβ (2.2σ) ratios than those with lower equivalent widths, implying lower gas-phase metallicities at a combined significance of 2.4σ. This implies a selection based on Lyα equivalent width is an efficient technique for identifying younger, less chemically enriched systems.