Mapping Dark Mattersu201727 | www.cfa.harvard.edu/
https://www.cfa.harvard.edu/news/su201727
Galaxies generally reside at the centers of vast clumps of dark matter called haloes because they surround the clusters of galaxies. Gravitational lensing
of more distant galaxies by dark matter haloes offers a particularly unique and powerful probe of the detailed distribution of dark matter. So-called strong
gravitational lensing creates highly distorted, magnified and occasionally multiple images of a single source; so-called weak lensing results in modestly yet
systematically deformed shapes of background galaxies that can also provide robust constraints on the distribution of dark matter within the clusters.
CfA astronomers Annalisa Pillepich and Lars Hernquist and their colleagues compared gravitationally distorted Hubble images of the galaxy cluster Abell 2744
and two other clusters with the results of computer simulations of dark matter haloes. They found, in agreement with key predictions in the conventional dark
matter picture, that the detailed galaxy substructures depend on the dark matter halo distribution, and that the total mass and the light trace each other.
They also found a few discrepancies: the radial distribution of the dark matter is different from that predicted by the simulations, and the effects of tidal
stripping and friction in galaxies are smaller than expected, but they suggest these issues might be resolved with more precise simulations. Overall, however,
the standard model of dark matter does an excellent and reassuring job of describing galaxy clustering.