A THEORETICAL INVESTIGATION OF GAMMA-RAY BURST HOST GALAXIES

Long-duration gamma-ray bursts (LGRBs) are believed to be linked with star formation. We adopt a galactic evolution model, in which the star formation process inside the virialized dark halo at a given redshift can be achieved. In this paper, gamma-ray burst (GRB) host galaxies are assumed to be star-forming galaxies within small dark halos. The star formation rates (SFRs) in the host galaxies of LGRBs at different redshifts have been derived from our model with a galactic evolutionary time at about a few times 107 yr, and a dark halo mass of about 5 x 1011 Msun. The related stellar masses, luminosities, and metallicities of these hosts are estimated as well. We further calculate the X-ray and optical absorption of GRB afterglow emission. From our model calculation, at higher redshift, the SFR of a host galaxy is larger, and the absorption in the X-ray and optical bands of a GRB afterglow is stronger, when the dust and metal components are locally released, surrounding the GRB environment. These model predictions are compared with Swift and other observational data. At lower redshift z < 1, as the merger and interaction of some host galaxies are involved, one monolithic physical process is not sufficient to fully explain all kinds of observed phenomena.