The star formation rate and metallicity of the host galaxy of the dark GRB 080325 at z = 1.78
- National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Department of Astronomy, California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
- Department of Astronomy, Kyoto University, Kyoto 606-8502 (Japan)
- Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720 (United States)
- Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan)
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 obtained spectrum provides a clear detection of Hα emission and marginal [Nii]λ6584. The host is a massive (M{sub *} ∼ 10{sup 11} M{sub ⊙}), dusty (A{sub V}∼1.2) star-forming galaxy at z = 1.78. The extinction-corrected star formation rate (SFR) calculated from the Hα luminosity (35.6–47.0 M{sub ⊙} yr{sup −1}) is typical among GRB host galaxies (and star-forming galaxies generally) at z > 1; however, the specific SFR is lower than for normal star-forming galaxies at redshift ∼1.6, in contrast to the high specific SFR measured for many of other GRB hosts. The metallicity of the host is estimated to be 12 + log(O/H){sub KK04} = 8.88. We emphasize that this is one of the most massive host galaxies at z >1 for which metallicity is measured with emission-line diagnostics. The metallicity is fairly high among GRB hosts, 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 likely cannot be 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 star formation rate. Thus, we conclude that metallicity is important to the mechanism that produced this GRB.
- OSTI ID:
- 22883005
- Journal Information:
- Astrophysical Journal, Vol. 806, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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