Year: 2015
Type: article
Abstract: Weak lensing can be observed through a number of effects on the images of distant galaxies; their shapes are sheared, sizes and fluxes (magnitudes) are magnified and positions on the sky are modified by the lensing field. Galaxy shapes probe the shear field whilst size, magnitude and number density probe the convergence field. Both contain cosmological information. In this paper, we are concerned with the magnification of sizes and magnitudes of individual galaxies as a probe of cosmic convergence. We develop a Bayesian approach for inferring the convergence field from measured sizes, magnitudes and redshifts and demonstrate that this inference requires detailed knowledge of the joint distribution of intrinsic sizes and magnitudes. We build a simple parametrized model for the size–magnitude distribution and estimate this distribution for CFHTLenS galaxies. In light of the measured distribution, we show that the typical dispersion on convergence estimation is ∼0.8, compared to ∼0.38 for shear. We discuss the possibility of physical systematics for magnification (similar to intrinsic alignments for shear) and compute the expected gains in the dark energy figure-of-merit (FoM) from combining magnification with shear for different scenarios regarding systematics: accounting for intrinsic alignments but no systematics for magnification, including magnification could improve the FoM by up to a factor of ∼2.5, whilst when accounting for physical systematics in both shear and magnification we anticipate a gain between ∼25 and ∼65 per cent. The fact that shear and magnification are subject to different systematics makes magnification an attractive complement to any cosmic shear analysis.
Institutions: Imperial College London, University College London
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: G2324855252, G4856069
OpenAlex ID: W1895086215