The effect of coupled dark energy on the alignment between dark matter and galaxy distributions in clusters

We investigate the effects of a coupled dark energy (cDE) scalar field on the alignment between satellites and matter distributions in galaxy clusters. Using high-resolution N-body simulations for ΛCDM and cDE cosmological models, we compute the probability density distribution for the alignment angle between the satellite galaxies and underlying matter distributions, finding a difference between the two scenarios. With respect to ΛCDM, in cDE cosmologies the satellite galaxies are less preferentially located along the major axis of the matter distribution, possibly reducing the tension with observational data. A physical explanation is that the coupling between dark matter and dark energy (DE) acts as an additional tidal force on the satellite galaxies, diminishing the alignments between their distribution and the matter one. Through a Wald test based on the generalized χ² statistics, the null hypothesis that the two probability distributions come from the same parent population is rejected at the 99% confidence level. It is concluded that the galaxy-matter alignment in clusters may provide a unique probe of dark sector interactions as well as the nature of DE.