'DARK' GRB 080325 IN A DUSTY MASSIVE GALAXY AT z {approx} 2
- 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)
- National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan)
- Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568 (Japan)
We present optical and near-infrared observations of Swift GRB 080325 classified as a 'dark gamma-ray burst (GRB)'. Near-infrared observations with Subaru/MOIRCS provided a clear detection of afterglow in the K{sub s} band, although no optical counterpart was reported. The flux ratio of rest-wavelength optical to X-ray bands of the afterglow indicates that the dust extinction along the line of sight to the afterglow is A{sub V} = 2.7-10 mag. This large extinction is probably the major reason for the optical faintness of GRB 080325. The J - K{sub s} color of the host galaxy, (J - K{sub s} = 1.3 in AB magnitude), is significantly redder than those for typical GRB hosts previously identified. In addition to J and K{sub s} bands, optical images in B, R{sub c} , i', and z' bands with Subaru/Suprime-Cam were obtained at about 1 year after the burst, and a photometric redshift of the host is estimated to be z {sub photo} = 1.9. The host luminosity is comparable to L* at z {approx} 2 in contrast to the sub-L* property of typical GRB hosts at lower redshifts. The best-fit stellar population synthesis model for the host shows that the red nature of the host is attributed to a large dust extinction (A{sub V} = 0.8 mag), and that the host galaxy is massive (M* = 7.0 x 10{sup 10} M {sub sun}), which makes it one of the most massive GRB hosts yet identified. By assuming that the mass-metallicity relation for star-forming galaxies at z {approx} 2 is applicable for the GRB host, this large stellar mass suggests the high-metallicity environment around GRB 080325, consistent with inferred large extinction.
- OSTI ID:
- 21455009
- Journal Information:
- Astrophysical Journal, Vol. 719, Issue 1; Other Information: DOI: 10.1088/0004-637X/719/1/378; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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