Revisiting the mass–metallicity relation and the fundamental metallicity relation of dwarf galaxies at cosmic noon with NIRISS

ABSTRACT We extend the stellar-mass gas-phase metallicity relation (MZR) at $z = 1.1\mathrm{ -}3.4$ down to the extremely low-mass regime using 183 galaxies with $\log (M_*/M_\odot) = 6.3\mathrm{ -}10.2$, based on deep JWST/NIRISS slitless spectroscopy from the NGDEEP program. The derived MZR is in excellent agreement with our previous result from 50 galaxies in the GLASS-JWST sample, underscoring the robustness and universality of this relation. Together, these data sets constitute the largest sample of dwarf galaxies yet obtained with NIRISS. The observed MZR slope, $\beta \simeq 0.24\pm 0.03$, remains constant across nearly four orders of magnitude in stellar mass. Analytical modelling of the metal-loading factor of outflows ($\zeta _\rm {out}$) indicates that, at $M_*\lesssim 10^8M_\odot$, $\zeta _\rm {out}$ becomes progressively less dominant than the gas fraction ($\mu _\rm {gas}$) in regulating the MZR slope. Using this enlarged NIRISS sample, we further test the existence of the fundamental metallicity relation (FMR). We find no robust evidence for an additional star formation rate (SFR) dependence beyond the MZR, nor any reduction in metallicity scatter when SFR is included. Examination of systematic uncertainties in $12+\log ({\rm O/H})$, $M_*$ and SFR suggests that the MZR slope ($\beta \sim 0.22$) is robust, and that different assumptions about the strong-line calibrations or star formation history of the galaxies change the slope by less than 1$\sigma$. At the current depth of the NIRISS data, evidence for an FMR among high-redshift dwarf galaxies remains inconclusive, highlighting the need for larger samples and deeper observations.