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

Abstract

Recent JWST/NIRSpec observations have 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 ($\log ({\mathrm{M}}_{\star }/{\mathrm{M}}_{\odot })\lesssim 9$) 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 $\sim 700$ [OIII]$\lambda 4363$ emitters with $\log ({\mathrm{M}}_{\star }/{\mathrm{M}}_{\odot })\lesssim 9$ at $z\sim 0$. We find no evidence of the FMR below $\log ({\mathrm{M}}_{\star }/{\mathrm{M}}_{\odot })\lesssim 9$ through any method, suggesting that slowly-evolving, quasi-steady state gas reservoirs are not yet established. We simultaneously find a weak positive correlation between metallicity and star formation, and that these systems are gas-rich with substantial diversity in effective yields ($y_{\mathrm{eff}}$) spanning $\sim 3\mathrm{dex}$. We demonstrate increasing $y_{\mathrm{eff}}$ correlates with decreasing FMR offsets, which in the context of the analytical and non-equilibrium gas models of Dalcanton et al. (2007), indicates a scenario where star formation bursts rapidly return and eject metals from the ISM before subsequent gas-balancing. Pristine infall diluting the ISM metal-content cannot lead to the $y_{\mathrm{eff}}$ diversity we measure, and thus is not the primary process behind FMR deviations. Our results suggest low-${\mathrm{M}}_{\star }$ systems, regardless of redshift, depart from a steady-state gas reservoir shaping the canonical FMR, in which metallicity variations are primarily driven by star formation and enriched outflows. With this characterization, we demonstrate $z\gtrsim 3$ [OIII]$\lambda 4363$ systems are indeed more metal-poor than $z\sim 0$ counterparts ($\Delta 12+\log (O/H)=0.3\mathrm{dex}$) at fixed ${\mathrm{M}}_{\star }$.

20 pages, 7 figures, submitted to the Astrophysical Journal

Cited by in corpus (1)

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