Cosmological simulations of two-component wave dark matter

Wave (fuzzy) dark matter (psi DM) consists of ultralight bosons, featuring a solitonic core within a granular halo. Here we extend psi DM to two components, with distinct particle masses m and coupled only through gravity, and investigate the resulting soliton-halo structure via cosmological simulations. Specifically, we assume psi DM contains 75 per cent major component and 25 per cent minor component, fix the major-component particle mass to m(major) = 1 x 10(-22) eV, and explore two different minor-component particle masses with m(major): m(minor) = 3: 1 and 1: 3, respectively. F or m(major): m(minor) = 3: 1, we find that (i) the major- and minor-component solitons coexist, have comparable masses, and are roughly concentric. (ii) The soliton peak density is significantly lower than the single-component counterpart, leading to a smoother soliton-to-halo transition and rotation curve. (iii) The combined soliton mass of both components follows the same single-component core-halo mass relation. In dramatic contrast, for m(major): m(minor) = 1: 3, a minor-component soliton cannot form with the presence of a stable major-component soliton; the total density profile, for both halo and soliton, is thus dominated by the major component and closely follows the single-component case. To support this finding, we propose a toy model illustrating that it is difficult to form a soliton in a hot environment associated with a deep gravitational potential. The work demonstrates that the e xtra fle xibility added to the multi-component psi DM model can resolve observational tensions over the single-component model while retaining its key features.

Automated summary

In this study, the wave (fuzzy) dark matter (psi DM) is extended to two components and their soliton-halo structure is investigated through cosmological simulations. The results show that when the proportion of the two components is 75% and 25%, both the major and minor component solitons coexist and have similar masses. However, when the proportion is 25% and 75%, a minor-component soliton cannot form. This work demonstrates the advantages of the multi-component psi DM model over the single-component model.