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“DARK” GRB 080325 IN A DUSTY MASSIVE GALAXY AT z ∼ 2

2010; IOP Publishing; Volume: 719; Issue: 1 Linguagem: Inglês

10.1088/0004-637x/719/1/378

1538-4357

T. Hashimoto, Kouji Ohta, Kentaro Aoki, Ichi Tanaka, Kiyoto Yabe, N. Kawai, Wako Aoki, Hisanori Furusawa, Takashi Hattori, Masanori Iye, Koji S. Kawabata, Naoto Kobayashi, Yutaka Komiyama, George Kosugi, Yosuke Minowa, Y. Mizumoto, Yuu Niino, K. Nomoto, Junichi Noumaru, Ryusuke Ogasawara, Tae‐Soo Pyo, T. Sakamoto, K. Sekiguchi, Y. Shirasaki, M. Suzuki, Akito Tajitsu, Tadafumi Takata, Toru Tamagawa, Hiroshi Terada, Tomonori Totani, J. Watanabe, Tōru Yamada, A. Yoshida,

Stellar, planetary, and galactic studies

We present optical and near infrared observations of GRB 080325 classified as a "Dark GRB". Near-infrared observations with Subaru/MOIRCS provided a clear detection of afterglow in Ks 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 Av = 2.7 - 10 mag. This large extinction is probably the major reason for optical faintness of GRB 080325. The J - Ks color of the host galaxy, (J - Ks = 1.3 in AB magnitude), is significantly redder than those for typical GRB hosts previously identified. In addition to J and Ks bands, optical images in B, Rc, i', and z' bands with Subaru/Suprime-Cam were obtained at about one year after the burst, and a photometric redshift of the host is estimated to be z_{photo} = 1.9. The host luminosity is comparable to L^{*} at z \sim 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 a large dust extinction (Av = 0.8 mag) attributes to the red nature of the host and that the host galaxy is massive (M_{*} = 7.0 \times 10^{10} Msun) which is one of the most massive GRB hosts previously identified. By assuming that the mass-metallicity relation for star-forming galaxies at z \sim 2 is applicable for the GRB host, this large stellar mass suggests the high metallicity environment around GRB 080325, consistent with inferred large extinction.