JADES-GS-z14-1: A Compact, Faint Galaxy at z ≈ 14 with Weak Metal Lines from Extremely Deep JWST MIRI, NIRCam, and NIRSpec Observations

JWST has shed light on galaxy formation and metal enrichment within 300 Myr of the Big Bang. While luminous galaxies at z > 10 often show significant [O III] λλ4959, 5007 emission lines, it remains unclear whether such features are prevalent among fainter, more typical galaxies due to observational limits. We present deep imaging and spectroscopy of JADES-GS-z14-1 at z_spec = 13.86⁺_{0.05 _}^0.04, currently the faintest spectroscopically confirmed galaxy at z ≈ 14. It serendipitously received 70.7 hr of MIRI/F770W imaging in the JWST Advanced Deep Extragalactic Survey (JADES), the deepest MIRI exposure for any high-redshift galaxy to date. Nonetheless, we detect only tentative F770W emission of 7.9 ± 2.8 nJy at 2.8σ significance, constraining the total equivalent width of [O III] λλ4959, 5007 + Hβ to 520⁺_{380 _}⁴⁰⁰ Å, weaker than most z > 10 galaxies with MIRI detections. This source is unresolved across 16 NIRCam bands, implying a physical radius ≲50 pc. NIRSpec/PRISM spectroscopy totaling 56 hr reveals no rest-frame ultraviolet emission lines above 3σ. Stellar population synthesis suggests a stellar mass ∼4 × 10⁷ M_☉ and a star formation rate ∼2 M_☉ yr⁻¹. The absence of strong metal emission lines despite intense star formation suggests a gas-phase metallicity below 10% solar and potentially a high escape fraction of ionizing photons. These deep observations provide rare constraints on faint, early galaxies, tracing the onset of chemical enrichment and ionization in the early Universe.