Measuring galaxy-galaxy-galaxy-lensing with higher precision and accuracy

Abstract

Context. Galaxy-galaxy-galaxy lensing (G3L) is a powerful tool for constraining the three-point correlation between the galaxy and matter distribution and thereby models of galaxy evolution. Aims. We propose three improvements to current measurements of G3L: (i) a weighting of lens galaxies according to their redshift difference, (ii) adaptive binning of the three-point correlation function, and (iii) accounting for the effect of lens magnification by the cosmic large-scale structure. Improvement (i) is designed to improve the precision of the G3L measurement, whereas improvements (ii) and (iii) remove biases of the estimator. We further show how the G3L signal can be converted from angular into physical scales. Methods. The improvements were tested on simple mock data and simulated data based on the Millennium Run with an implemented semi-analytic galaxy model. Results. Our improvements increase the signal-to-noise ratio by 35% on average at angular scales between 0.′1 and 10′ and physical scales between 0.02 and 2 h−1 Mpc. They also remove the bias of the G3L estimator at angular scales below 1′, which was originally up to 40%. The signal due to lens magnification is approximately 10% of the total signal.