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Astronomy Colloquium (2019 Fall Semester)

* Date
Sept 04 (Wednesday)
* Speaker
Dr. Bomee Lee (Caltech)
* Title
Probing the nature of dark matter through measurements of galaxy shapes
* Abstract
 

Euclid is a 1.2m optical/near-infrared space telescope designed to understand the expansion and growth history of the universe and is scheduled to launch in 2022. Measuring weak gravitational lensing (WL), a powerful probe of the distribution of large scale structure, is one of the primary science goals of Euclid and other future large extragalactic surveys with LSST and WFIRST. In order to reconstruct a three dimensional weak lensing map of dark matter in different redshift bins, it is crucial to constrain both galaxy shapes and photometric redshifts very well. Currently, the WL analysis has primarily been based on optical band imaging, limiting results to z<1; Euclid and LSST will detect cosmic shear with optical imaging over many thousands of square degrees. However, near-infrared (NIR) imaging has never been used for wide-field weak lensing measurement outside of cluster fields. In this talk, I will present advantages to using NIR bands for WL measurements.  First, I will show the advantages of measuring galaxy shapes in the NIR with Euclid-quality images simulated from Hubble Space Telescope (HST) images. Second, I will introduce new color-constrained galaxy templates, which improve the photometric redshifts for future surveys which will only have limited number of bands at the relevant sensitivities. I will conclude with plans for future work. These include the first z > 1 weak lensing map of dark matter distribution in a blank field with the largest set of HST NIR images, which will serve as a critical stepping stone for NIR shear measurements with upcoming space-based WL surveys with Euclid and WFIRST.