Wave dark matter and ultra-diffuse galaxies

• Published in: Monthly notices of the Royal Astronomical Society Vol. 504; no. 2; pp. 2868 - 2876
• Main Authors: Pozo, Alvaro, Broadhurst, Tom, de Martino, Ivan, Luu, Hoang Nhan, Smoot, George F, Lim, Jeremy, Neyrinck, Mark
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01-06-2021; Oxford University Press (OUP): Policy P - Oxford Open Option A
• Subjects: Astrophysics; Bose-Einstein condensates; Compact galaxies; Context; Dark matter; Dwarf galaxies; Physics; Scalars; Solitary waves; Spheroidal galaxies; Spheroids; String theory; dark matter; velocity: dispersion; condensation: Bose-Einstein; star; soliton: ground state; halo; structure; field theory: scalar; galaxy: mass; density: low; string model; excited state; axion; galaxy: dark matter
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stab855

ABSTRACT
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’ (ψDM) 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 ≃33 km s−1, extending to at least 3 kpc, that we show is reproduced by our ψDM simulations with a soliton radius of ≃0.5 kpc. In the ψDM 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.