CfA Colloquium: October 3, 2002

Speaker: Paul Schechter (MIT)

Title: The Milli- and Micro-lensing of Macrolensed Quasars

Abstract: The 0th, 1st and 2nd derivatives of a "Fermat potential" give the three D's of gravitational lensing: delay, deflection and distortion. Observations of these delays, deflections and distortions make it possible to model the gravitational potentials of the intervening galaxies which produce multiple images of distant quasars. Simple models for lensing potentials that successfully reproduce image positions to high accuracy fail ABYSMALLY in reproducing the flux ratios of the multiple images, suggesting the presence of small scale structure within the lensing galaxies. It has been argued that the flux ratio anomalies observed at radio wavelengths signal the presence of CDM mini-halos. We argue that the yet larger anomalies observed at optical wavelengths can result from microlensing by stars, but ONLY if a substantial fraction of the projected mass is in a smooth, dark component.

Reference for students: astro-ph/0204425
Schechter, P.L. and Wambsganss, J. 2002, "Quasar Microlensing at High Magnification and the Role of Dark Matter: Enhanced Fluctuations and Suppressed Saddlepoints"