A New Challenge for Dark Matter Models

Understand

Cold dark matter (CDM) has faced a number of challenges mainly at small scales, such as the too-big-to-fail problem, and core-cusp density profile of dwarf galaxies.

• Such problems were argued to have a solution either in the baryonic physics sector or in modifying the nature of dark matter to be self-interacting, or self-annihilating, or ultra-light.
• Here we present a new challenge for CDM by showing that two of Milky Way's satellites (Horologium I, and Tucana II) are too dense, requiring the formation masses and redshifts of halos in CDM not compatible with being a satellite.
• These too-dense-to-be-satellite systems are dominated by dark matter and exhibit a surface density above mean dark energy cosmic surface density $\sim\Omega_{\Lambda} \rho_c c/H_0\approx 600~\rm M_{\odot}/pc^2$.