PI: Eric Agol, University of Washington, firstname.lastname@example.org
Address: Department of Astronomy, Box 351580, Seattle, WA 98195, USA
CoI: Christopher S. Kochanek, The Ohio State University
Title: Searching for Substructure
Abstract: We propose to measure the mid-IR flux ratios of the quasar images in six gravitational lenses using NIRI, Michelle and TReCS. Mid-IR measurements are the key to understanding why gravitational lenses show peculiar flux ratios compared to the expectations from plausible models for the primary lens galaxy. Mid-IR fluxes are unaffected by propagation effects in the lens galaxy (e.g. extinction for the optical or scattering for the radio), or small-scale perturbations to the gravitational field (i.e. microlensing due to stars). If the flux ratio anomalies seen in the radio/optical persist in the mid-IR, then they must be due to low mass satellites/CDM substructure in the lens galaxy rather than a propagation effect. If the flux ratio anomalies seen in the optical vanish in the mid-IR, then they are due to microlensing by the stars and we can estimate the relative surface densities of stars and dark matter near the images. For the systems where the anomalies are due to microlensing we will use the reappearance of the anomaly going from the mid-IR to the near-IR to study the structure of quasar accretion disks.
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