A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: Implications for H₀

Abstract

Strong gravitational lensing provides an independent measurement of the Hubble parameter (H 0 ). One remaining systematic is a bias from the additional mass due to a galaxy group at the lens redshift or along the sightline. We quantify this bias for more than 20 strong lenses that have well-sampled sightline mass distributions, focusing on the convergence κ and shear γ. In 23% of these fields, a lens group contributes 1% convergence bias; in 57%, there is a similarly significant line-of-sight group. For the nine time-delay lens systems, H 0 is overestimated by 11 2 3 -+ % on average when groups are ignored. In 67% of fields with total 0.01  k , line-of-sight groups contribute 2 ´more convergence than do lens groups, indicating that the lens group is not the only important mass. Lens environment affects the ratio of four (quad) to two (double) image systems; all seven quads have lens groups while only 3 of 10 doubles do, and the highest convergences due to lens groups are in quads. We calibrate the γ-κ relation: log 1.94 0.34 log tot tot) with an rms scatter of 0.34 dex. Although shear can be measured directly from lensed images, unlike convergence, it can be a poor predictor of convergence; for 19% of our fields, κ is 2  g. Thus, accurate cosmology using strong gravitational lenses requires precise measurement and correction for all significant structures in each lens field.

Milliarcsecond X-ray astrometry to resolve inner regions of AGN at $z>1$ using gravitational lensing

“…Chandra observations of CLASS B0712+472 were carried out on 2003 December 17 (Ob-sID 4199) for 97.7 ks live time (Fassnacht et al 2008), for the purpose of studying a foreground group of galaxies at z = 0.29. See also Momcheva et al (2015); Wilson et al (2017), for other data on these groups, concurring that the group at z = 0.29 had a minimal effect on the lensed images as reported by Fassnacht & Lubin (2002). Fassnacht et al (2008) reported X-ray detection of three images out of the four, with images A and B blended together due to their small angular separation of about 0.…”

Cosmograil

“…A prior on M/L is given by the enclosed mass within the Einstein radius, tightly constrained by the visible arc in the lens images. McCully et al (2017) find, using flexion-shift calculations, that the nearby group plays an important role; it is thus explicitly modeled using a NFW profile, using priors based on the position and velocity dispersion measured by Wilson et al (2017). To assess the importance of the lens modeling on our microlensing time delay estimates, we also perform our analysis using the parameters proposed in Table 1 of Morgan et al (2008) for a stellar fraction f M/L of 0.7 and 0.8 and find similar results.…”

Price of shifting the Hubble constant

“…In the case of strong lensing time delays, the determination of the time delay distance requires a determination of the density profile of the lens and the line of sight [39], but there are several potentially dangerous degeneracies in the construction of the lens model [40,41] from the observed source positions. To break these degeneracies in the determination of the lens profile, one generally uses the line of sight velocity dispersion.…”