Dynamics of galactic halos with self-interacting, ultralight dark matter particles

In this work, the existing solver for ultralight dark matter, also called scalar-field dark matter, PyUltraLight (Edwards et al. (2018)) was extended by the self-interaction, which was then named PyUltraLight_SI. In addition, a tool called density_profile was developed, which uses the simulation data to create radial density profiles. With this package, various aspects of scalar-field dark matter with and without self-interaction were examined. Thus, ideal box size-resolution-pairs for single solitons without self-interaction and an axion mass of 10^−22 eV/c2 up to a mass of ∼ 6.6 · 10^8M⊙ were found, which were also extended to multi-soliton simulations. Furthermore, the behavior of solitons at rest (meaning no interactions or initial dynamics) and over a period of 150 Gyr was analyzed. It was found, that solitons began to oscillate from a certain mass, with the quantum pressure of the model being assumed to be the reason. In addition, it could be observed that the relaxation time of solitons made from scalar-field dark matter must be very long, since solitons were still not relaxed even after 150 Gyr. In addition to single-soliton simulations, simulations with multiple solitons were also performed. The main focus here lied on mergers and it was analyzed, how the initial configuration affects the central density. It was found that mergers with direct collisions had a lower central density. A simulation was also carried out with a larger axion mass of 10^−21 eV/c2, in which it was found that a soliton with higher axion mass but smaller soliton mass results in a higher central density. For the simulations with self-interaction, a central density-soliton mass-relation was found for a dimensionless self-coupling constant Λ ^{^} = 0.02, which predicts a lower central density for more massive solitons. Finally, an attempt was made to carry out simulations with Thomas-Fermi-scalar field dark matter. But this failed, since the required, significant increase in Λ ^{^} was not possible. Thus, only a maximum of Λ ^{^} = 10 could be reached. It could be observed that solitons with a repulsive self-interaction expand over time and their density profiles become more uniform. (author)