Strong‐Lensing Time Delay: A New Way of Measuring Cosmic Shear

Abstract

The phenomenon of cosmic shear, or distortion of images of distant sources unaccompanied by magnification, is an effective way of probing the content and state of the foreground universe, because light rays do not have to pass through matter clumps in order to be sheared. It is shown that the delay in the arrival times between two simultaneously emitted photons that appear to be arriving from a pair of images of a strongly lensed cosmological source contains not only information about the Hubble constant, but also the long-range gravitational effect of galactic-scale mass clumps located away from the light paths in question. This is therefore also a method of detecting shear. Data on time delays among a sample of strongly lensed sources can provide crucial information about whether extra dynamics beyond gravity and dark energy are responsible for the global flatness of space. If the standard ÃCDM model is correct, there should be a large dispersion in the value of H 0 as inferred from the delay data by (the usual procedure of ) ignoring the shear from all other mass clumps except the strong lens itself. The fact that there has not been any report of a significant deviation from the h ¼ 0:7 mark during any of the H 0 determinations by this technique may already be pointing to the absence of the random effect discussed here.

New multiple AGN systems with subarcsec separation: Confirmation of candidates selected via the novel GMP method

“…Variability and time lag. given the small projected separation (0.25 ), in the case of lensing, the time delay between components A and B is 2 days at most (Lieu 2008). For intrinsic variability to be at the origin of the differences above, this timescale must be larger than (or of the same order of) the size of the broad-line emitting region (BLR).…”

Gravitational lenses as cosmic rulers: $\mathsf{\Omega_{m}}$, $\mathsf{\Omega_{\Lambda}}$ from time delays and velocity dispersions

“…Nevertheless, like for any cosmic ruler, there is a range of possible systematic uncertainties which must be addressed before it can be used for precision cosmology. Several factors affect the lensing configuration, the velocity dispersion, and the time delays to various degrees: velocity anisotropy, total massprofile shape (Schwab et al 2009) and the detailed density structures (mass profiles of dark and luminous matter, ellipticities) of the lenses (Tonry 1983), mass along the line of sight to the QSO (Lieu 2008) and in the environment of the lenses, such as groups and clusters (Metcalf 2005) (the mass-sheet degeneracy (Saha 2000;Falco et al 1985;Williams & Saha 2000;Oguri 2007)) and substructure (Dalal & Kochanek 2002;Macciò & Miranda 2006;Macciò 2006;Xu 2009). These factors are of the order of our assumed measurement uncertainties.…”

A New Channel for Detecting Dark Matter Substructure in Galaxies: Gravitational Lens Time Delays

“…We have drawn the preliminary conclusion that uncertainties in the angular structure of the lens potential can be dealt with, using additional flux ratios data and/or independent constraints on the shapes of galaxy mass distributions. Other potential concerns may include the environment of the lens galaxy (Keeton & Zabludoff 2004), and (sub)structure along the line of sight (Keeton 2003;Chen et al 2003;Metcalf 2005a,b;Lieu 2008). For all of these issues, the important point is again that non-local features in the lens potential affect the images in some coordinated way, whereas substructure affects the images differently.…”