We present a recalibration of the luminosity-metallicity relation for gas-rich , star-forming dwarfs to magnitudes as faint as M _ { R } \sim -13 .
We use the metallicity calibrations to calibrate the relation for all of the data in this analysis .
In metallicity-luminosity space we find two sub-populations within a sample of high-confidence SDSS DR8 star-forming galaxies ; 52 % are metal-rich giants and 48 % are metal-medium galaxies .
Metal-rich dwarfs classified as tidal dwarf galaxy ( TDG ) candidates in the literature are typically of metallicity 12 + log ( O/H ) = 8.70 \pm 0.05 , while SDSS dwarfs fainter than M _ { R } = -16 have a mean metallicity of 12 + log ( O/H ) = 8.28 \pm 0.10 , regardless of their luminosity , indicating that there is an approximate floor to the metallicity of low luminosity galaxies .
Our hydrodynamical simuations predict that TDGs should have metallicities elevated above the normal luminosity-metallicity relation .
Metallicity can therefore be a useful diagnostic for identifying TDG candidate populations in the absence of tidal tails .
At magnitudes brighter than M _ { R } \sim -16 our sample of 53 star-forming galaxies in 9 H i gas-rich groups is consistent with the normal relation defined by the SDSS sample .
At fainter magnitudes there is an increase in dispersion in metallicity of our sample , suggestive of a wide range of H i content and environment .
In our sample we identify three ( 16 % of dwarfs ) strong TDG candidates ( 12 + log ( O/H ) > 8.6 ) , and four ( 21 % ) very metal poor dwarfs ( 12 + log ( O/H ) < 8.0 ) , which are likely gas-rich dwarfs with recently ignited star formation .