An Investigation into the Low-mass Fundamental Metallicity Relation in the Local and High- z Universe

Journal article

Recent JWST/NIRSpec observations revealed high-z star-forming galaxies depart from the fundamental metallicity relation (FMR), yet the z = 0 FMR has not been well-characterized in the low-mass regime ( log(M⋆/M⊙)≲9 ) for an appropriate comparison of low- and high-z systems. We attempt to rectify this limitation through a meta-analysis, providing a local, observational comparison for future high-z FMR studies. We analyzed common FMR fitting methods for ∼4000 [O III] λ4363 emitters, with the majority being below log(M⋆/M⊙)=9 at z ∼ 0 where the canonical FMR has not been well explored. We find no evidence of the canonical FMR in this low-mass regime through any method, suggesting that slowly evolving, quasi-steady state gas reservoirs are not yet established in these systems. We find a weak positive correlation between metallicity and star formation, and that these systems are gas-rich with substantial diversity in effective yields (yeff) spanning ∼1.5 dex. We demonstrate that increasing yeff correlates with decreasing FMR offsets, which, combined with the nonequilibrium gas models of Dalcanton et al., suggests that star formation bursts rapidly return and eject metals from the ISM before subsequent gas balancing. Pristine infall cannot lead to the yeff diversity we measure, and thus is not the primary process behind FMR deviations. With this characterization, we demonstrate z ≳ 2 [O III] λ4363 systems are indeed more metal-poor than z ∼ 0 counterparts ( Δ12+log(O/H)=0.3dex ) at fixed M⋆.

Authors: Laseter, IH; Maseda, MV; Bunker, AJ; Cameron, AJ; Curti, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: The Astrophysical Journal
• Volume: 1007
• Issue: 1
• Pages: 26-26
• Publication date: 2026-08-03
• DOI: 10.3847/1538-4357/ae7d25
• EISSN: 1538-4357
• ISSN: 0004-637X
• Language: English
• Keywords: Interstellar medium; Universe; Equation of state; Star (game theory); Metallicity; Galaxy