THE STATE AND PROPERTIES OF THE INTERSTELLAR MEDIUM IN GRB HOST GALAXIES

摘要

Spectroscopic studies of GRB host galaxies can provide us with information about the environment of the GRB and allow to study high-redshift galaxies otherwise inaccessible for a closer investigation. Emission line measurements of low redshift hosts seem to confirm the picture that GRBs only occur in metal-poor dwarf galaxies or at least metal-poor regions of larger galaxies and metallicity seems to be an important ingredient for the collapsar-model to work. Afterglow spectra of high-redshift hosts, however, show a generally higher metallicity, a higher density of neutral hydrogen and different properties of metal absorption lines compared to e.g. QSO absorbers. Distance indicators lead to the conclusion that most of the absorbing material observed is far away from the GRB site tracing the normal ISM in the host galaxies.