Measuring Mass Distributions in Moderate-Redshift Galaxies Through Gravitational Lensing

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Dr Fassnacht will use strong gravitational lensing, the bending of light as it passes close to a massive object, to study the mass distributions of massive elliptical galaxies, probing back to times when the cosmos was roughly half as old as it is now. The velocity dispersion of the stars in the foreground 'lensing' galaxy will be measured using multislit spectrographs on the Keck telescopes in the optical and in the near-infrared. Uncommitted slits will be used to measure redshifts of galaxies lying nearby on the sky, to study any group or cluster surrounding the lens. Hubble Space Telescope images will be used to measure the weak lensing distortions for galaxies whose light passes 100kpc or more from the central lens, probing the massive dark halo of the lensing galaxy. Finally, adaptive optics imaging on the Keck telescopes will be used to search for faint companions to the lens galaxy. Brightness ratios for the images are often discrepant from what would be expected for a smooth elliptical lens, suggesting that companions may be present. Dr Fassnacht has already used this technique to find a faint companion to one lens galaxy. A graduate student and undergraduate researchers will participate in the research. Dr Fassnacht will continue his program of public-outreach talks, and he will introduce astronomy to an existing program at UC Davis for high school students.