Ultralight axion dark matter: dynamical relaxation, and predicted accretion and density profiles around central solitons in galaxies

Jordi Miralda-Escudé (ICC, Universitat de Barcelona)

 

Ultralight axions have been proposed as a candidate for a constituent of the dark matter. This would imply that dark matter in galaxies oscillates like a classical wave with wavelengths on galactic scales. As the amplitudes in the modes of these waves are dynamically relaxed, we predict that a steady-state distribution is established that gives rise to a central soliton (the self-gravitating ground state of the wave) plus a surrounding corona with a density profile falling as r^{-5/3}, analogous to the Bahcall-Wolf cusp of a stellar cluster around a central black hole. The formation of these structures can be tested in cosmological simulations and should be present in dark matter halos if the dark matter has an ultralight axion component.