Magnification Bias Estimators for Realistic Surveys: an Application to the BOSS Survey

Abstract

In addition to the intrinsic clustering of galaxies themselves, the spatial distribution of galaxies observed in surveys is modulated by the presence of weak lensing due to matter in the foreground. This effect, known as magnification bias, is a significant contaminant to analyses of galaxy-lensing cross-correlations and must be carefully modelled. We present a method to estimate the magnification bias in spectroscopically confirmed galaxy samples based on finite differences of galaxy catalogues while marginalizing over errors due to finite step size. We use our estimator to measure the magnification biases of the CMASS and LOWZ samples in the SDSS BOSS galaxy survey, analytically taking into account the dependence on galaxy shape for fiber and PSF magnitudes, finding ${\alpha }_{\mathrm{CMASS}}=2.71\pm 0.02$ and ${\alpha }_{\mathrm{LOWZ}}=2.45\pm 0.02$ and quantify modelling uncertainties in these measurements. Finally, we quantify the redshift evolution of the magnification bias within the CMASS and LOWZ samples, finding a difference of up to a factor of three between the lower and upper redshift bounds for the former. We discuss how to account for this evolution in modelling and its interaction with commonly applied redshift-dependent weights. Our method should be readily-applicable to upcoming surveys and we make our code publicly available as part of this work.

arXiv comment14 pages, 9 figures, 3 tables, Accepted in MNRAS

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• Accurate Measurement of the Lensing Magnification by BOSS CMASS Galaxies and Its Implications for Cosmology and Dark Matter
• Challenges in Cosmic Magnification Reconstruction by Magnification Response
• Linear Relativistic Corrections in the Spherical Fourier-Bessel Power Spectrum
• Weak Lensing Reconstruction by Counting DECaLS Galaxies
• Doppler bias: impact of peculiar velocities on color selection and the large scale structure of galaxy surveys