Cosmological systematics beyond nuisance parameters: form-filling functions

T. D. Kitching, A. Amara, F. B. Abdalla, B. Joachimi, A. Refregier, Thomas Kitching

Research output: Contribution to journalArticlepeer-review

Abstract

In the absence of any compelling physical model, cosmological systematics are often misrepresented as statistical effects and the approach of marginalizing over extra nuisance systematic parameters is used to gauge the effect of the systematic. In this article, we argue that such an approach is risky at best since the key choice of function can have a large effect on the resultant cosmological errors. As an alternative we present a functional form-filling technique in which an unknown, residual, systematic is treated as such. Since the underlying function is unknown, we evaluate the effect of every functional form allowed by the information available (either a hard boundary or some data). Using a simple toy model, we introduce the formalism of functional form filling. We show that parameter errors can be dramatically affected by the choice of function in the case of marginalizing over a systematic, but that in contrast the functional form-filling approach is independent of the choice of basis set. We then apply the technique to cosmic shear shape measurement systematics and show that a shear calibration bias of |m(z)|
Original languageEnglish
Pages (from-to)2107-2128
JournalMonthly Notices of the Royal Astronomical Society
Volume399
DOIs
Publication statusPublished - 1 Nov 2009

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