Lyα absorbers in motion: consequences of gravitational lensing for the cosmological redshift drift experiment★

The nature of intermediate-redshift damped Lyα absorbers

We present HST/WFPC2 high-spatial resolution images in the R and B bands of the close environment of the sightlines to seven quasars which spectra show either a damped Lyα absorption line, 21 cm absorption, or a very strong Mg ii/Fe ii absorption system at intermediate redshifts (0.4 ≤ z ≤ 1). Objects down to about 0.3′′, or 2.0 kpc at z = 0.6 (H0 = 50 kms s−1 Mpc−1, q0 = 0), and to a limiting ...

Cosmological Applications of Gravitational Lensing

The last decade has seen an enormous increase of activity in the eld of gravitational lensing, mainly driven by improvements of observational capabilities. I will review the basics of gravitational lens theory, just enough to understand the rest of this contribution, and will then concentrate on several of the main applications in cosmology. Cluster lensing, and weak lensing, will constitute th...

Cosmological Applications of Gravitational Lensing

Metal Lines in Cosmological Models of Lyα Absorbers

The metal absorption lines found in association with Lyα absorbers of moderate to high HI column density contain valuable information about the metallicity and ionization conditions within the absorbers and offer a stronger test of models of the intergalactic medium at z ∼ 3 than HI absorption lines alone. We have developed a method to predict the strengths of metal absorption lines within the ...

Gravitational lensing in galaxy redshift surveys

Gravitationally-lensed quasars are both valuable (individually and statistically) and rare. They are mostly discovered through time-consuming re-imaging of known quasars, but can also be found spectroscopically in galaxy redshift surveys. Q 2237+0305 (Huchra et al. 1985) was found in this manner, but remains the only such discovery. Kochanek (1992) predicted that ∼ 1 in 10 redshifts would yield...