Damped Lyman-Alpha Absorption in Q0957+561A, B

Abstract

A series of archival IUE low-dispersion spectral observations of the double quasar Q0957 + 561A, B are analyzed. The components of this gravitationally lensed quasar are separated by ~6". Damped Lyα absorption at redshift z_abs_ = 1.3911 with neutral hydrogen column density N(H I) ~ 7 x 10^19^ cm^-2^ is present in the spectra of both the A and B components. Using an accepted model by Young et al. for the gravitational lens, the damped Lyα absorber is inferred to have a minimum size of ~0.5h^-1^_50_ kpc. The standard interpretation is that a damped Lyα absorber represents a galactic or protogalactic H I disk. In the context of this standard model, the absorption-line properties and evidence for Faraday rotation are discussed.