AR_final file_2018-19

quads to date and paves the way for a variety of studies. To illustrate the scientific content of the sample, they have investigated the alignment be- tween the mass and light distribution in the deflec- tors. The position angles of these distributions are well-aligned, except when there is strong external shear. However, they find no correlation between the ellipticity of the light and mass distributions. It is also shown that the observed flux-ratios be- tween the images depart significantly from the pre- dictions of simple smooth models. The departures are strongest in the bluest band, consistent with mi- crolensing being the dominant cause in addition to millilensing. Future research will exploit this rich data set in combination with ground-based spec- troscopy and time delays to determine quantities such as the Hubble constant, the free streaming length of dark matter, and the normalization of the initial stellar mass function. Search for lensed quasars in Pan- STARRS1 Anupreeta More and collaborators have carried out a systematic search for gravitationally lensed quasars in Pan-STARRS1. The final sample of can- didates comprises of 91 systems. They have also rediscovered 25 lensed quasars and quasar pairs. Amongst the independently discovered quads is 2M1134 2103, for which they have obtained spec- troscopy for the first time, finding a redshift of 2.77 for the quasar. There is evidence for microlensing due to stars from the lensing galaxy in at least one image. They have performed detailed mass mod- elling of this system using archival imaging data. It is found that the unusal configuration of lensed images can be explained due to a faint companion galaxy (4 arcsec away), and a galaxy group/cluster (30 arcsec away). Constraining the mass density of free- floating black holes Strong gravitational lensing of active galactic nu- clei, at radio wavelengths, can result in razor-thin arcs, with angular widths of less than a milli- arcsecond, if observed at the resolution achiev- able with very long baseline interferometry (VLBI). Such razor-thin arcs provide a unique window on the coarseness of the matter distribution between a distant source in the background and observer on Earth. Anupreeta More , Surhud More and collaborators investigate to what extent such razor- thin arcs can constrain the number density and mass function of free-floating black holes, defined as black holes that do not, or no longer, reside at the centre of a galaxy. These black holes can be either primordial in origin or arise as by-products of the evolution of supermassive black holes in galactic nuclei. When sufficiently close to the line of sight, free-floating black holes cause kink-like distortions in the arcs, which are visually detectable in the VLBI images as long as the black hole mass exceeds 1000 solar masses. Using a crude estimate for the detectability of such distortions, they analytically compute constraints on the matter density of free- floating black holes resulting from non-detections of distortions along a realistic, fiducial arc, and find them to be comparable to those from quasar milli- lensing. They also use predictions from a large hy- drodynamical simulation for the demographics of free-floating black holes that are not primordial in origin and show that their predicted mass density is roughly four orders of magnitude below the con- straints achievable with a single razor-thin arc. Environments and line-of-sight struc- tures of lensing galaxies Anupreeta More and collaborators have inves- tigated the local and line-of-sight overdensities of strong gravitational lens galaxies using wide-area multiband imaging from the Hyper Suprime-Cam Subaru Strategic Program. They present 41 new definite or probable lens candidates discovered in Data Release 2 of the survey. Using a combined sample of 87 galaxy-scale lenses out to a lens red- shift of ∼ 0 . 8, they compare galaxy number counts in lines of sight toward known and newly discov- ered lenses in the survey to those of a control sam- ple consisting of random lines of sight. They also compare the local overdensity of lens galaxies to a sample of “twin” galaxies that have a similar red- ( 68 )