AAS 205th Meeting, 9-13 January 2005
Session 147 Groups and Clusters of Galaxies
Poster, Thursday, January 13, 2005, 9:20am-4:00pm, Exhibit Hall

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[147.18] Improvements in Galaxy Shape Measurements by Simultaneously Fitting Individual Exposures

C. Roat, D. Wittman, A.J. Tyson (UC Davis)

A new technique is presented for fitting the shapes of galaxies that have been imaged in multiple exposures. Instead of the traditional approach of co-adding several exposures to produce a single image for measurements, this method simultaneously analyzes all individual exposures to determine the galaxy shape and size that best fits all images of a particular galaxy. This process effectively uses knowledge about the point spread function of individual exposures, taking advantage of the detailed information present in highly resolved images, while still extracting the limited information available in images with poorer resolution. This is important for lensing surveys with a range of seeing conditions.

The simultaneous fit is performed using a maximum likelihood technique that combines the likelihoods calculated from each individual exposure. The RooFit Toolkit for Data Modeling, based on the ROOT data analysis framework, is used as the engine for the fitting procedure. Improvement in measurement error is characterized by its dependence on the size, the shape, and the signal to noise ratio of the galaxy, as well as on the seeing conditions in which the exposures were taken. The final figure of merit for a lensing survey is the inverse shear variance per square arcminute, which scales as the effective density of usable sources, neff. The improvement in neff is quantified for realistic galaxy size and seeing distributions using images from the Deep Lens Survey and simulated images for the Large Synoptic Survey Telescope as testbeds.

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© 2004. The American Astronomical Society.