Abstract
ABSTRACT Gravitational lensing magnification modifies the observed spatial distribution of galaxies and can severely bias cosmological probes of large-scale structure if not accurately modelled. Standard approaches to modelling this magnification bias may not be applicable in practice as many galaxy samples have complex, often implicit, selection functions. We propose and test a procedure to quantify the magnification bias induced in clustering and galaxy–galaxy lensing (GGL) signals in galaxy samples subject to a selection function beyond a simple flux limit. The method employs realistic mock data to calibrate an effective luminosity function slope, αobs, from observed galaxy counts that can then be used with the standard formalism. We demonstrate this method for two galaxy samples derived from the Baryon Oscillation Spectroscopic Survey (BOSS) in the redshift ranges 0.2 < z ≤ 0.5 and 0.5 < z ≤ 0.75, complemented by mock data built from the MICE2 simulation. We obtain αobs = 1.93 ± 0.05 and αobs = 2.62 ± 0.28 for the two BOSS samples. For BOSS-like lenses, we forecast a contribution of the magnification bias to the GGL signal between the multipole moments, ℓ, of 100 and 4600 with a cumulative signal-to-noise ratio between 0.1 and 1.1 for sources from the Kilo-Degree Survey (KiDS), between 0.4 and 2.0 for sources from the Hyper Suprime-Cam survey (HSC), and between 0.3 and 2.8 for ESA Euclid-like source samples. These contributions are significant enough to require explicit modelling in future analyses of these and similar surveys. Our code is publicly available within the MagBEt module (https://github.com/mwiet/MAGBET).
Highlights
Over the last few decades, weak gravitational lensing has become a powerful tool to directly measure the matter distribution of the late Universe, while allowing for the inference of the cosmological parameters which govern it
This paper aims to provide a method for estimation of the magnification bias for surveys which have complex sample selection functions which are not purely flux/magnitude-limited
The method outlined in this paper aims to provide an accurate estimate of the effective luminosity function slope, α, of a galaxy sample with a complex sample selection
Summary
Over the last few decades, weak gravitational lensing has become a powerful tool to directly measure the matter distribution of the late Universe, while allowing for the inference of the cosmological parameters which govern it Surveys, such as the currently ongoing Kilo Degree Survey (KiDS, Kuijken et al 2015), the Dark Energy Survey (DES, Flaugher et al 2015), the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP, Aihara et al 2018), have become increasingly limited by systematics rather than statistics as ever-growing sample sizes reduce uncertainties. Rubin Observatory Legacy Survey of Space and Time (LSST, Abell et al 2009), and the Nancy Grace Roman Space Telescope ( known as WFIRST, Spergel et al 2015) For this reason, recent efforts have focused on improving our physical understanding of often neglected phenomena which can influence cosmological parameter inference based on shear and clustering measurements. We will focus on the magnification effects
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