POWRE: Dark Matter Halos: Lensing Profiles and Merger Histories

Harvard University, Cambridge MA

Investigators

Abstract

AST-0074728 Cohn The structure in the universe evolves as the universe expands. Small fluctuations present in the very early universe have grown under the influence of gravity and other forces to form all the stars, galaxies, superclusters, etc. that we see around us today. Dr. Cohn will be investigating structure formation by concentrating on the properties of dark matter halos, that is, clustered dark matter. Dr. Cohn will study profiles of dark matter by using data from observed strong gravitational lens systems in the case where the lens is a galaxy. In strong gravitational lensing, the mass of the galaxy has bent the light approaching us from a more distant source so much that we see multiple images of the source. The positions and brightness of the multiple images of the source depend in part on how matter is distributed in the lensing galaxy, and thus these positions and fluxes can be analyzed to find the dark matter structure of the galaxy. The collection of discovered lenses will be used to build up a statistical sample of mass profiles present in the universe at different eras and environments. In addition, if the source varies with time, the images will vary as well. The time delay between the image variations can be used, together with the mass profile for the lensing galaxy, to calculate a fundamental cosmological parameter, the Hubble constant, which characterizes the rate of expansion of the universe today. Dr. Cohn will also study mergers of dark matter halos on larger scales by using numerical simulations. She will simulate the gravitational collapse, and thus the growth of initial small fluctuations, to model and study large structures of the size of galaxy groups and clusters. The focus of these simulations will be to characterize the merging properties of' the clustered dark matter and to quantify the amount and importance of merging in the evolution of these structures. This project is funded by the Division of Astronomical Sciences and the Office of Multidisciplinary Activities in the Mathematical and Physical Sciences Directorate. ***