Direct measurement of dark matter halo ellipticity of massive clusters
A Subaru Suprime-Cam image of one of the clusters used in the analysis, A2390, (2.7 billion light years from the Earth). The purple hue shows the dark matter distribution measured by the gravitational lensing effect on distant galaxies (typically 8 billion light years from the Earth), where the darker color indicates the denser dark matter concentration. It shows that the dark matter distribution is elongated along the northwest-southeast direction.
We conducted weak lensing analysis using a full use of the two-dimensional (2D) lensing signals obtained from high-quality Subaru/Suprime-Cam imaging data. The elliptical shape of dark matter haloes is detected at 7sigma significance level. The mean ellipticity is in excellent agreement with a theoretical prediction based on the standard collisionless cold dark matter model.