Weak lensing magnification in the Dark Energy Survey Science Verification Data

TL;DR

This study detects weak lensing magnification effects on galaxy counts in DES data, confirming predictions of the ΛCDM model with high significance and proposing a method to optimize signal detection.

Contribution

It presents the first detection of weak lensing magnification in DES SV data and introduces a new method to select samples with maximum signal-to-noise ratio.

Findings

Detected magnification signal at 3.5σ significance in multiple bands

Results are consistent with ΛCDM model predictions

Method for selecting optimal samples validated with data

Abstract

In this paper the effect of weak lensing magnification on galaxy number counts is studied by cross-correlating the positions of two galaxy samples, separated by redshift, using data from the Dark Energy Survey Science Verification dataset. The analysis is carried out for two photometrically-selected galaxy samples, with mean photometric redshifts in the $0.2 < z < 0.4$ and $0.7 < z < 1.0$ ranges, in the riz bands. A signal is detected with a $3.5\sigma$ significance level in each of the bands tested, and is compatible with the magnification predicted by the $\Lambda$CDM model. After an extensive analysis, it cannot be attributed to any known systematic effect. The detection of the magnification signal is robust to estimated uncertainties in the outlier rate of the pho- tometric redshifts, but this will be an important issue for use of photometric redshifts in magnification mesurements from larger samples. In addition to the detection of the magnification signal, a method to select the sample with the maximum signal-to-noise is proposed and validated with data.