Wave dark matter and ultra-diffuse galaxies

Dark matter (DM) as a Bose-Einstein condensate, such as the axionic scalar field particles of String Theory, can explain the coldness of DM on large scales. Pioneering simulations in this context predict a rich wave-like structure, with a ground state soliton core in every galaxy surrounded by a halo of excited states that interfere on the de Broglie scale. This de Broglie scale is largest for the low-mass galaxies as momentum is lower, providing a simple explanation for the wide cores of dwarf spheroidal galaxies. Here we extend these 'wave dark matter' (psi DM) predictions to the newly discovered class of 'ultra-diffuse galaxies' (UDG) that resemble dwarf spheroidal galaxies but with more extended stellar profiles. Currently, the best-studied example, 'Dragon Fly 44' (DF44), has a uniform velocity dispersion of similar or equal to 33 kms(-1), extending to at least 3 kpc, that we show is reproduced by our psi DM simulations with a soliton radius of similar or equal to 0.5 kpc. In the psi DM context, we show that relatively flat dispersion profile of DF44 lies between massive galaxies with compact dense solitons, as may be present in the Milky Way on a scale of 100 pc and lower mass galaxies where the velocity dispersion declines centrally within a wide, low-density soliton, like Antlia II, of radius 3 kpc.

Automated summary

Dark matter as a Bose-Einstein condensate explains its coldness on large scales, with simulations predicting wave-like structures in galaxies. The theory extends to ultra-diffuse galaxies resembling dwarf spheroidal galaxies, showing a uniform velocity dispersion and soliton radius in simulation. This 'wave dark matter' model provides insights into the dispersion profiles of different galaxies.