The Dust - To - Gas Ratio of z > 0 Galaxies Through Gravitational Lenses

We report the detection of differential gas column densities in three gravitational lenses, MG 0414+0534, HE 1104−1805, and PKS 1830−211. Combined with the previous differential column density measurements in B 1600+434 and Q 2237+0305 and the differential extinction measurements of these lenses, we probe the dust-to-gas ratio of a small sample of cosmologically distant normal galaxies. We obtain an average dust-to-gas ratio of E(B−V )/NH= (1.4± 0.5)× 10 mag cm atoms with an estimated intrinsic dispersion in the ratio of ≃ 40%. This average dust-to-gas ratio is consistent with the average Galactic value of 1.7 × 10 mag cm atoms and the estimated intrinsic dispersion is also consistent with the 30% observed in the Galaxy. Subject headings: dust-to-gas ratio