The main author Dr. Linke and I have submitted a paper to A&A on a new application for galaxy-galaxy-galaxy lensing (G3L). Weak gravitational lensing is a statistical method to probe the elusive dark matter density field and its relation to visible galaxies, embedded inside matter halos. Here we show that the G3L signal that looks at the mean tangential gravitational shear around galaxy pairs can be used to constrain the average halo-occupation distribution of the pairs inside matter halos. The upshot is: in addition to the mean number of galaxies per halo, we now also can constrain the correlation of galaxy satellite numbers inside the halos for galaxy pairs made up of different galaxy populations. This provides input for galaxy models and may help to improve cosmological analyses that rely on galaxies as tracers.
We successfully apply this technique to data from the KiDS+GAMA+VIKING collaborations and show that pairs of red and blue lenses as well as pairs of galaxies with different stellar masses have positively correlated satellite numbers inside (dark-)matter halos. As expected from semi-analytical models for galaxies, the correlation amplitude decreases with halo mass, but is nevertheless clearly present in galaxy clusters. For instance, pairs of red and blue galaxies, basically objects with long ceased star formation and those with recent star formation, reach a (Pearson) correlation coefficient of around r~+0.4 -- barely negligible as presumed in several previous studies.