Astroseminar - Alexandra Amon - VIA ZOOM

 Alexandra Amon, based at Princeton University, is primarily interested in understanding the evolution and composition of the Universe, including its dark components. She is an expert in weak lensing, working very closely with data and has a keen interest in the intersection with large-scale structure surveys. She co-leads the weak lensing team in the Dark Energy Survey (DES) and is focused on developing techniques further for the upcoming Rubin Observatory LSST.  She has previously held postdoctoral fellowships at Cambridge University and Stanford University, and obtained her PhD from the University of Edinburgh.

Title: Weak lensing with a billion galaxies: new opportunities, challenges and strategies

Abstract: Weak gravitational lensing provides an immense opportunity to test the standard cosmological model and to probe astrophysics. Over the last decade, it has matured as a high-precision tool with on-going surveys like the Dark Energy Survey, which has imaged 5000 sq degrees and 100M galaxies. Intriguingly, weak lensing surveys have consistently reported a mild cosmological tension:  low values of the clustering amplitude parameter  (S_8) compared to that predicted by Planck primary Cosmic Microwave Background. In this talk, I will highlight the unique potential of lensing to test of the non-linear regime of the cosmological model, to constrain  baryonic effects like AGN feedback, and to measure the halo masses of galaxies . On the eve of Rubin Observatory’s Legacy Survey of Space and Time (LSST), which will measure weak lensing with billions of galaxies, the challenge is clear: systematics must be controlled to make the most of the next epic decade of data. I will present on-going efforts to calibrate observations, in particular, the photometric redshifts of the galaxy sample, and to understand and mitigate astrophysical systematic effects.  Finally, I will demonstrate new approaches for testing the scale-dependence of cosmological observations, understanding baryonic feedback, and measuring the masses of dwarf galaxies using lensing data in tandem with spectroscopic surveys like the Dark Energy Spectroscopic Instrument (DESI).