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Scientific Seminars

[Astro] The rise and fall of spectroscopy in weak lensing experiments

by William Hartley (Geneva University)


Abstract: A measurement of the parameters that governing the expansion history of the universe via weak gravitational lensing requires two key ingredients: a two-point function of galaxy shape measurements and the redshift distributions of the galaxy samples involved in the analysis. As weak lensing surveys grew in statistical precision, the demand for improved redshift estimates also grew. Teams supplemented, or even replaced, the largely model-based methods of obtaining redshifts favour of directly utilising the highly accurate measurements possible via spectroscopy. In recent years, the importance of systematic effects in the use of spectroscopic data has become apparent, leading to a decline in their use. I will provide an overview of the evolving use of spectroscopy as weak lensing methodology and surveys have developed, focussing on a subtle but critical selection effect that all but forbids their role in the Dark Energy Survey. I will then discuss how spectroscopy may yet find a central role in the weak lensing experiments of the near future