The mass profile of galaxy clusters out to ~2 r200

We analyze the internal dynamics of 43 non-interacting clusters which are selected from the 2dF Galaxy Redshift Survey 100k public release. We join together the 43 clusters into an ensemble cluster by appropriately scaling their galaxy velocities and clustercentric distances. We solve the Jeans equation for the hydrostatic equilibrium for the member galaxies within the virial radius of the ensemble cluster, assuming isotropic orbits. We constrain the cluster mass profile within the virial radius by exploring parameterized models for the cluster mass-density profile. We find that both cuspy profiles and profiles with a core are acceptable. In particular, the concentration parameter of the best fit NFW model is as predicted from numerical simulations in a LambdaCDM cosmology. Density profiles with very large core-radii are ruled out. Beyond the virial radius, dynamical equilibrium cannot be taken for granted, and the Jeans equation may not be applicable. In order to extend our dynamical analysis out to ~2 virial radii, we rely upon the method which uses the amplitude of caustics in the space of galaxy clustercentric distances and velocities. We find very good agreement between the mass profile determined with the caustic method and the extrapolation to ~2 virial radii of the best-fit mass profile determined by the Jeans analysis in the virialized inner region. We determine the mass-to-number density profile, and find it is fully consistent with a constant within the virial radius. The mass-to-number density profile is however inconsistent with a constant when the full radial range from 0 to ~2 virial radii is considered, unless the sample used to determine the number density profile is restricted to the early-type galaxies.Comment: To be published in ApJ - 20 pages, 9 figure

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements