Program: GN-2018A-FT-213

Long duration gamma-ray bursts (LGRBs), i.e. those GRBs associated with the deaths of massive stars, show a strong preference for low-metallicity environments. Indeed, our previous work shows that LGRBs are formed roughly thirty times more frequently per unit star formation below a metallicity of 1/3 solar than above 1/3 solar. However, the uncertainties on these rates are large and because our present sample is inhomogenous, some biases remain. Here we propose to finish an essentially complete sample of host metallicities out to z = 0.5. The full sample will nearly double the number of published host metallicities in this range. This will largely eliminate systematic uncertainties, as our sample will contain all known LGRBs with z< 0.47 and be complete down to host absolute magnitudes of M_V ~ -18 out to z<0.5. Because we are using significant archival data, as well as data we have obtained in the South using the VLT, we can complete our sample with about 8.5 hours of Gemini North time.