We present optical and near infrared observations of Swift GRB 080325 classified as a “ Dark GRB ” .
Near-infrared observations with Subaru/MOIRCS provided a clear detection of afterglow in K _ { 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 _ { V } = 2.7 - 10 mag .
This large extinction is probably the major reason for optical faintness of GRB 080325 .
The J - K _ { s } color of the host galaxy , ( J - K _ { s } = 1.3 in AB magnitude ) , is significantly redder than those for typical GRB hosts previously identified .
In addition to J and K _ { s } bands , optical images in B , R _ { c } , 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 ( A _ { V } = 0.8 mag ) attributes to the red nature of the host and that the host galaxy is massive ( M _ { * } = 7.0 \times 10 ^ { 10 } M _ { \odot } ) 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 .