My girlfriend made a presentation summarizing her REU experience. It is about gravitational lensing and the work she did trying to distinguish characteristics of lenses caused by galactic clusters. That is the best summary I can give.

1. Gravitational Lensing in Clusters of Galaxies Stefanie A. Gallegos Dr. Michael Gladders

2. What are gravitational lenses? A gravitational lens is the result of the bending of light from a distant source around a massive object Giant arcs are the result of strong lensing Deviation angle is a function of the mass of the lens (more mass=larger angle) and the observer-lens-source geometry Credit: SDSS Credit: Gemini Credit: Gemini

3. Research Motivation Credit: SDSS Credit: Gemini Lenses are very rare events Can be predicted in detail from simulations Great way to see background universe (objects that are too faint) Help further define cosmological parameters and understand the nature of dark matter

4. Research Goals Credit: Gemini Credit: Gemini Theory suggests that lensing clusters are a biased (concentrated, aligned etc.) subset of all clusters. QUESTION: Do we see any evidence in the galaxy population of lensing clusters to suggest that this is true?

8. Conclusions Magnitude differences between central galaxies of lensing sample vs. comparison sample  Lensing clusters have much more luminous central galaxies! Positional offsets are smaller in lensing clusters  Lensing clusters are more relaxed

10. Future Prospects Shapes, concentration and substructure Cluster mass estimates With this data supporting common characteristics of lensing clusters, it will be easier to identify them in future surveys. Mass to light ratios dark matter halos Credit: KICP Giant Arcs Collaboration Effort