Galaxy-scale lenses with measured time delays can be used to determine the Hubble constant, given an accurate lens model. However, perturbations from structures along the line of sight can introduce errors into the measurement. Using data from a survey towards known lenses in group environments, we generate fiducial lines of sight and insert mock lenses with assumed input physical and cosmological parameters. These parameters can be recovered with ~5-10% scatter when uncertainties in my characterization of the environment are applied. The lenses in groups have larger bias and scatter. We predict how well new time delay lenses from LSST will constrain H_0 and find that an ensemble of 500 quad lenses will recover H_0 with ~2% bias and ~0.3% precision.
On larger scales, galaxy cluster lenses can magnify the earliest galaxies into detectability. While past studies have focused on single massive clusters, we investigate the properties of lines of sight, or "beams", containing multiple cluster-scale halos in projection. Even for beams of similar total mass, those with multiple halos have higher lensing cross sections on average. The optimal configurations for maximizing the cross section are also those that maximize faint z ~ 10 detections. I present a new selection technique to identify beams in wide-area photometric surveys that contain high total masses and often multiple clusters in projection as traced by luminous red galaxies. I apply this technique to the Sloan Digital Sky Survey and present the 200 most promising beams. Several are confirmed spectroscopically to be among the highest mass beams known with some containing multiple clusters. These are among the best fields to search for faint high-redshift galaxies.回上一頁