We report J -band MOSFIRE spectroscopy of a low-mass ( \text { log } ( M _ { * } / M _ { \odot } ) = 8.62 ^ { +0.10 } _ { -0.06 } ) star-forming galaxy at z = 0.997 showing the detection of [ N II ] and [ S II ] alongside a strong H \alpha line .
We derive a gas-phase metallicity of \text { log } ( \text { O } / \text { H } ) = 7.99 ^ { +0.13 } _ { -0.23 } , placing this object in a region of M _ { * } - Z space that is sparsely populated at this redshift .
Furthermore , many existing metallicity measurements in this M _ { * } - z regime are derived from only [ N II ] /H \alpha ( N2 ) , a diagnostic widely used in high-redshift metallicity studies despite the known strong degeneracy with the ionization parameter and resulting large systematic uncertainty .
We demonstrate that even in a regime where [ N II ] and [ S II ] are at the detection limit and the measurement uncertainty associated with the [ N II ] / [ S II ] ratio is high ( S / N \approx 3 ) , the more sophisticated Dopita et al .
diagnostic provides an improved constraint compared to N2 by reducing the systematic uncertainty due to the ionization parameter .
This approach does not , however , dispel uncertainty associated with stochastic or systematic variations in the nitrogen-to-oxygen abundance ratio .
While this approach improves upon N2 , future progress in extending metallicity studies into this low-mass regime will require larger samples to allow for stochastic variations , as well as careful consideration of the global trends among dwarf galaxies in all physical parameters , not just metallicity .