(Proposal ID) S15A-036

(PI) Niino, Yuu

(Proposal Title)
 The complete metallicity measurements of long GRB host galaxies at z < 0.5

(Abstract)
We propose to obtain spectra of long gamma-ray burst (GRB) host galaxies at 
redshifts < 0.5 and measure their metallicities, to understand the nature of 
long GRB progenitor stars. Although many GRB host galaxies were 
spectroscopically studied in the past few years, the targets of the 
observations were selected non-uniformly by various researchers. Despite the 
increasing number of the spectroscopic sample, the non-uniform selection of 
the targets makes it difficult to discuss the metallicity distribution of the 
long GRB host galaxies quantitatively. There are ~ 20 long GRBs with known 
redshift < 0.5 and sufficient localization to identify their host galaxies, 
and 1/3 of them are without sufficient spectroscopic observation deep enough 
to determine metallicity of the host galaxy. We aim to measure metallicity of 
all GRB host galaxies with known redshift < 0.5. The sample enables us to 
discuss the metallicity distribution function of the long GRB host galaxies 
in a quantitative way for the first time.