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Gravitational Lensing as a Cosmological Probe

Final Report Summary - GLENCO (Gravitational Lensing as a Cosmological Probe)

The GLENCO project has been developing new methods for simulating, detecting and studying gravitational lensing. The gravitation lensing is in turn used to study things ranging from the structure of quasars to the evolution of the energy density of the universe. A major effort has been put into developing powerful computer tools that make gravitational lensing simulations easier and more realistic and allow us to extract scientific information from gravitational lensing. Our code GLAMER incorporates novel techniques for lensing simulations making it possible to preform simulations with stars, halos, analytic galaxy models or from the output of large scale cosmological simulations or with any combination of these. This simulation platform has allowed us to investigate how theories that explain dark energy can be distinguished with weak lensing data from future imaging surveys of the sky like the Euclid satellite and LSST (Large Synaptic Survey Telescope). It has also enabled us to investigate how invisible structures within the distribution of dark matter affect the images of strongly lensed galaxies and quasars which has important implications for the properties of dark matter. We have also been doing simulations of strong lenses for the purpose of training and testing methods for finding and analyzing such objects in future these surveys. This simulation effort has provided a large number of high quality lensing simulations of all kinds to the research community .

To extract scientific information form strong gravitational lenses (ones where the images of background galaxy is highly distorted and there are multiple images of a single object) requires a lens modeling code. This has been another focus of our work. We developed a unique tool called LENSED which utilizes the speed of massively parallel GPUs (graphics processing units) to make unprecedentedly detailed models of “Einstein ring” lenses – lenses where the image of the background galaxy is distorted into arcs or a nearly complete ring by the gravity of a foreground object. This has allowed us to extract new information about the distribution of dark matter in several cases and there will be many more to come. For the first time we have been able to measure the steepness of the dark matter mass profile at a radius well beyond the visible galaxy. This is a valuable and unique confirmation of the standard dark matter theory, cold dark matter or CDM.

The GLENCO team has also developed new a technique for measuring weak lensing at high redshifts using low frequency radio observations. Our new method should make it possible to measure the lensing power spectrum at redshifts of 1 to 5 in future 21 cm observations without having to resolve the individual galaxies using the planned Square Kilometer Array (SKA) telescopes. This relies on a mode of observation known as 21 cm intensity mapping. Indications are that this will be one of the few ways to probe dark energy at redshifts beyond one.