We derive direct measurement gas-phase metallicities of 7.4 < 12 + \log ( O / H ) < 8.4 for 14 low-mass Emission Line Galaxies ( ELGs ) at 0.3 < z < 0.8 identified in the Faint Infrared Grism Survey ( FIGS ) .
We use deep slitless G102 grism spectroscopy of the Hubble Ultra Deep Field ( HUDF ) , dispersing light from all objects in the field at wavelengths between 0.85 and 1.15 microns .
We run an automatic search routine on these spectra to robustly identify 71 emission line sources , using archival data from VLT/MUSE to measure additional lines and confirm redshifts .
We identify 14 objects with 0.3 < z < 0.8 with measurable O [ iii ] \lambda 4363 Å emission lines in matching VLT/MUSE spectra .
For these galaxies , we derive direct electron-temperature gas-phase metallicities with a range of 7.4 < 12 + \log ( O / H ) < 8.4 .
With matching stellar masses in the range of 10 ^ { 7.9 } M _ { \odot } < M _ { \star } < 10 ^ { 10.4 } M _ { \odot } , we construct a mass-metallicity ( MZ ) relation and find that the relation is offset to lower metallicities compared to metallicities derived from alternative methods ( e.g. , R _ { 23 } , O3N2 , N2O2 ) and continuum selected samples .
Using star formation rates ( SFR ) derived from the H \alpha emission line , we calculate our galaxies ’ position on the Fundamental Metallicity Relation ( FMR ) , where we also find an offset toward lower metallicities .
This demonstrates that this emission-line-selected sample probes objects of low stellar masses but even lower metallicities than many comparable surveys .
We detect a trend suggesting galaxies with higher Specific Star Formation ( SSFR ) are more likely to have lower metallicity .
This could be due to cold accretion of metal-poor gas that drives star formation , or could be because outflows of metal-rich stellar winds and SNe ejecta are more common in galaxies with higher SSFR .