# The Most Powerful Lenses in the Universe: Quasar Microlensing as a Probe of the Lensing Galaxy **Authors:** David Pooley (Trinity University), Timo Anguita (Universidad Andres, Bello), Saloni Bhatiani (University of Oklahoma), George Chartas (College of, Charleston), Matthew Cornachione (United States Naval Academy), Xinyu Dai, (University of Oklahoma), Carina Fian (Instituto de Astrof\'isica de, Canarias, Universidad de la Laguna), Evencio Mediavilla (Instituto de, Astrof\'isica de Canarias, Universidad de la Laguna), Christopher Morgan, (United States Naval Academy), Ver\'onica Motta (Instituto de F\'isica y, Astronom\'ia, Universidad de Valpara\'iso), Leonidas A. Moustakas (Jet, Propulsion Laboratory, California Institute of Technology), Sampath Mukherjee, (University of Groningen), Matthew J. O'Dowd (Lehman College, City University, of New York), Karina Rojas (Ecole Polytechnique F\'ed\'erale de Lausanne,, LSSTC Data Science Fellow), Dominique Sluse (STAR institute, Universit\'e of, Li\`ege), Georgios Vernardos (University of Groningen), and Rachel Webster, (University of Melbourne) arXiv: 1904.12968 · 2019-05-01 ## TL;DR This paper discusses how optical and X-ray observations of gravitationally lensed quasars can reveal the distribution of matter in lensing galaxies, including stars, black holes, and dark matter sub-halos, especially with upcoming surveys. ## Contribution It proposes a method combining optical and X-ray data to measure the ratio of smooth to clumpy matter in lensing galaxies across a range of redshifts. ## Key findings - Future surveys will discover hundreds of quadruply lensed quasars. - X-ray observations can determine the matter composition in lensing galaxies. - This approach can calibrate the stellar mass-to-light ratio in these galaxies. ## Abstract Optical and X-ray observations of strongly gravitationally lensed quasars (especially when four separate images of the quasar are produced) determine not only the amount of matter in the lensing galaxy but also how much is in a smooth component and how much is composed of compact masses (e.g., stars, stellar remnants, primordial black holes, CDM sub-halos, and planets). Future optical surveys will discover hundreds to thousands of quadruply lensed quasars, and sensitive X-ray observations will unambiguously determine the ratio of smooth to clumpy matter at specific locations in the lensing galaxies and calibrate the stellar mass fundamental plane, providing a determination of the stellar $M/L$. A modest observing program with a sensitive, sub-arcsecond X-ray imager, combined with the planned optical observations, can make those determinations for a large number (hundreds) of the lensing galaxies, which will span a redshift range of $\sim$$0.25