Abstract

Column densities of the highly-ionized species, C IV, N V and O VI, observed in the interstellar medium in the high redshift (z > 2) GRB host galaxies are analyzed using the non-equilibrium (time-dependent) photoionized model. It is found that the ionic ratios measured in the observations cannot be obtained with the photoionization model with super-solar metallicity. The possible ways to explain the observed ionic ratios are discussed.