JADES: Insights into the low-mass end of the mass–metallicity–SFR relation at 3 &lt; <i>z</i> &lt; 10 from deep JWST/NIRSpec spectroscopy

Abstract

We analysed the gas-phase metallicity properties of a sample of low-stellar-mass (log M ⋆ / M ⊙ ≲ 9) galaxies at 3 &lt; z &lt; 10 observed with JWST/NIRSpec as part of the JADES programme in its deep GOODS-S tier. By combining this sample with more massive galaxies at similar redshifts from other programmes, we study the scaling relations between stellar mass ( M ⋆ ), oxygen abundance (O/H), and star-formation rate (SFR) for 146 galaxies spanning three orders of magnitude in stellar mass and out to the epoch of early galaxy assembly. We find evidence for a shallower slope at the low-mass end of the mass–metallicity relation (MZR), with 12+log(O/H) = (7.72 ± 0.02) + (0.17 ± 0.03) log( M ⋆ /10 8 M ⊙ ), in good agreement with the MZR probed by local analogues of high-redshift systems, such as the ‘Green Pea’ and ‘Blueberry’ galaxies. The inferred slope is well matched by models including ‘momentum-driven’ supernova (SN) winds, suggesting that feedback mechanisms in dwarf galaxies (and at high z ) might be different from those in place at higher masses. The evolution in the normalisation is observed to be relatively mild compared to previous determinations of the MZR at z ∼ 3 (∼0.1 − 0.2 dex across the explored mass regime). We observe a deviation from the local fundamental metallicity relation (FMR) for our sample at high redshift, especially at z &gt; 6, with galaxies significantly less enriched than predicted given their M ⋆ and SFR (with a median offset in log(O/H) of ∼0.5 dex, significant at ∼5 σ ). These observations are consistent with an enhanced stochasticity in the gas accretion and star-formation history of high-redshift systems, prompting us to reconsider the nature of the relationship between M ⋆ , O/H, and SFR in the early Universe.