The Star Formation Rate and Metallicity of the Host Galaxy of the Dark Grb 080325 at Z=1.78
Hashimoto Tetsuya1*, Ohta Koji2
1Institute of Astronomy, National Tsing Hua University, Hsinchu, Taiwan
2Department of Astronomy, Kyoto University, Kyoto, Japan
* presenting author:Tetsuya Hashimoto, email:tetsuya@phys.nthu.edu.tw
We present near-infrared spectroscopy of the host galaxy of the dark gamma-ray burst (GRB) 080325
using Subaru/Multi-Object Infrared Camera and Spectrograph. The host is a massive dusty star-forming
galaxy at z = 1.78. The metallicity is fairly high (12+log(O/H)=8.88 based on KK04 calibration)
among GRB hosts in contrast to the theoretical low-metallicity requirement, however, this is still
lower than the metallicity of normal star-forming galaxies of the same mass at z ~1.6. The metallicity
offset from normal star-forming galaxies is close to a typical value of other GRB hosts and indicates
that GRB host galaxies are uniformly biased toward low metallicity over a wide range of redshifts and
stellar masses. The low-metallicity nature of the GRB 080325 host is unlikely attributed to the fundamental metallicity relation of star-forming galaxies because it is a metal-poor outlier from the relation and has a low specific SFR. Thus, we conclude that low metallicity is important to the mechanism that produced this GRB.


Keywords: Galaxy, GRB