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Magnification Bias Corrections to Galaxy-Lensing Cross-Correlations

R. Ziour 1 L. Hui
APC (UMR_7164) - AstroParticule et Cosmologie, Institut für theoretische Physik
Abstract : Galaxy-galaxy or galaxy-quasar lensing can provide important information on the mass distribution in the universe. It consists of correlating the lensing signal (either shear or magnification) of a background galaxy/quasar sample with the number density of a foreground galaxy sample. However, the foreground galaxy density is inevitably altered by the magnification bias due to the mass between the foreground and the observer, leading to a correction to the observed galaxy-lensing signal. The aim of this paper is to quantify this correction. The single most important determining factor is the foreground redshift z: the correction is small if the foreground galaxies are at low redshifts but can become non-negligible for sufficiently high redshifts. For instance, we find that for the multipole l=1000, the correction is above 1%*(5s-2)/b for z<0.37, and above 5%*(5s-2)/b for z<0.67, where s is the number count slope of the foreground sample, and b its galaxy bias. These considerations are particularly important for geometrical measures, such as the Jain and Taylor ratio or its generalization by Zhang et al. Assuming (5s-2)/b=1, we find that the foreground redshift should be limited to z<0.45 in order to avoid biasing the inferred dark energy equation of state w by more than 5%, and that even for a low foreground redshift (< 0.45), the background samples must be well separated from the foreground to avoid incurring a bias of similar magnitude. Lastly, we briefly comment on the possibility of obtaining these geometrical measures without using galaxy shapes, using instead magnification bias itself.
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Submitted on : Monday, September 22, 2008 - 1:48:47 PM
Last modification on : Wednesday, October 21, 2020 - 4:32:13 PM

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R. Ziour, L. Hui. Magnification Bias Corrections to Galaxy-Lensing Cross-Correlations. Physical Review D, American Physical Society, 2008, 78, pp.123517. ⟨10.1103/PhysRevD.78.123517⟩. ⟨in2p3-00323518⟩



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