Theoretical predictions for observational signatures of granulation in wave dark matter

Abstract

As of now, dark matter is about 85\% of the mass in our Universe, but we do not know its true nature. In galaxies and galaxy clusters for example, it is thought to be distributed in the form of a ``halo" which surrounds the galactic disc and extends beyond the visible component of a galaxy. When dark matter is distributed in many smaller ``halos" throughout a galaxy, we can call them sub-halos. The conventional model for dark matter, known as `cold dark matter' (CDM), has trouble explaining two main observations, first of which is the shallow mass density profiles for galaxies. CDM also predicts a large number of low-mass satellite galaxies which are yet to be observed. A new model called wave dark matter (\PsiDM) which is composed of a non-relativistic Bose-Einstein condensate has been shown to not have the two main problems that CDM has. Its wave-like properties lead to quantum interference between the dark matter ``waves", which in turn produce solitonic (non-dissipative waves) cores at the center of galaxies, along with mass granulations at smaller scales. This has been shown recently by the first simulation of wave dark matter.

The aim of my research is to theoretically investigate the gravitational lensing signatures of wave dark matter in observations, particularly those of the granulations produced due to the quantum interference. There are many lensing observations which have difficulty in being explained using current lens models. I use high-performance computing facilities to run numerical simulations of the theoretical lensing effects of wave dark matter granulations. After obtaining a 3D power spectrum for the mass distribution of the granulations, I calculate the 2D projected power spectrum. Using this power spectrum, I create a Gaussian random field which describes the mass fluctuations of the granulations. Using the mass distribution, deflection angles and therefore magnifications are calculated. I carried out these simulations for a wide range of dark matter halo masses, which corresponds to varying granulation wavelengths. My results show that complex patterns are created in both the critical curves (regions of theoretically infinite magnification) and images of background sources. These patterns are capable of producing significant changes in magnification relative to a model without granulations, as well as producing changes to image shape and size. These features may help in explaining many observations where current lens models are not so successful. They also give us more insight into the nature of dark matter. Future work will study the statistical nature of the patterns created by the wave dark matter granulations, and carry out a quantitative comparison of the predicted phenomena with observations.