Lensing Corrections to Features in the Angular Two-Point Correlation Function and Power Spectrum

TL;DR

This paper studies how gravitational lensing magnification bias distorts the observed galaxy correlation function and power spectrum, especially affecting features like the matter-radiation equality peak and baryon wiggles, with implications for precision cosmology.

Contribution

It provides a detailed quantification of lensing-induced distortions in the angular correlation function and power spectrum, highlighting their dependence on redshift, galaxy bias, and source distribution.

Findings

Lensing corrections increase with redshift and are larger for steep number count slopes.

Significant shifts in the matter-radiation equality scale occur at z > 1.5, reaching up to 30%.

Baryon wiggles are shifted by less than 1%, with width increases around 10%.

Abstract

It is well known that magnification bias, the modulation of galaxy or quasar source counts by gravitational lensing, can change the observed angular correlation function. We investigate magnification-induced changes to the shape of the observed correlation function w(\theta) and the angular power spectrum C_{\ell}, paying special attention to the matter-radiation equality peak and the baryon wiggles. Lensing mixes the correlation function of the source galaxies with the matter correlation at the lower redshifts of the lenses. Since the lenses probe structure nearer to the observer, the angular scale dependence of the lensing terms is different from that of the sources, thus the observed correlation function is distorted. We quantify how the lensing corrections depend on the width of the selection function, the galaxy bias b, and the number count slope s. The correction increases with redshift and larger corrections are present for sources with steep number count slopes and/or broad redshift distributions. The most drastic changes to C_{\ell} occur for measurements at z >~1.5 and \ell <~ 100. For the source distributions we consider, magnification bias can shift the matter-radiation equality scale by 1-6% at z ~ 1.5 and by z ~ 3.5 the shift can be as large as 30%. The baryon bump in \theta^2w(\theta) is shifted by <~ 1% and the width is typically increased by ~10%. Shifts of >~ 0.5% and broadening of >~ 20% occur only for very broad selection functions and/or galaxies with (5s-2)/b>~2. However, near the baryon bump the magnification correction is not constant but a gently varying function which depends on the source population. Depending on how the w(\theta) data is fitted, this correction may need to be accounted for when using the baryon acoustic scale for precision cosmology.