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

We analysed the gas-phase metallicity properties of a sample of low-stellar-mass ($\mathrm{log}_{10}(M_{\ast}/M_{\odot}) \leq 9$ ) galaxies at $3 < z < 10$ 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 ($M_{\ast}$ ), oxygen abundance ($\mathrm{O/H}$ ), 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 $12 + \mathrm{log}_{10}(\mathrm{O/H}) = (7.72 \pm 0.02) + (0.17 \pm 0.03)\,\mathrm{log}_{10}(M_{\ast}/10^{8}\,M_{\odot})$ ), 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 $\mathrm{high}-z$ ) 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 $z \sim 3$ ($\sim 0.1-0.2\ \mathrm{dex}$ across the explored mass regime). We observe a deviation from the local fundamental metallicity relation (FMR) for our sample at high redshift, especially at $z > 6$ , with galaxies significantly less enriched than predicted given their $M_{\ast}$ and SFR (with a median offset in $\mathrm{log}_{10}(\mathrm{O/H})$ of $\sim 0.5\ \mathrm{dex}$ , significant at $\sim 5\sigma$ ). 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 $M_{\ast}$ , $\mathrm{O/H}$ , and SFR in the early Universe.

Astronomy & Astrophysics, Volume 684, id.A75, 22 pages