Probing the Dust‐to‐Gas Ratio ofz> 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 and extinction measurements in B1600+434 and Q2237+0305, 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 )/ N H = (1.4 ± 0.5) × 10 -22 mag cm 2 atoms -1 , 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 -22 mag cm 2 atoms -1 , and the estimated intrinsic dispersion is also consistent with the 30% observed in the Galaxy.