The metallicity properties of long-GRB hosts

The recently-discovered Fundamental Metallicity Relation (FMR), which is the tight dependence of metallicity on both mass and SFR, proves to be a very useful tool to study the metallicity properties of various classes of galaxies. We have used the FMR to study the galaxies hosting long-GRBs. While the GRB hosts have lower metallicities than typical galaxies of the same mass, i.e., they are below the mass-metallicity relation, they are fully consistent with the FMR. This shows that the difference with the mass-metallicity relation is due to higher than average SFRs, and that GRBs with optical afterglows do not preferentially select low-metallicity hosts among the star-forming galaxies.