New and old probes of dark matter scenarios on galactic and sub-galactic scales

Abstract

This review focuses on novel astrophysical probes of dark matter at galactic and sub-galactic scales. After reviewing classical tests of cold dark matter (CDM) in galaxy formation, we discuss them in light of recent results from increasingly detailed simulations and observations, and then shift our attention to more recent, less explored tests in the context of the most popular and most studied dark matter scenarios alternative to CDM. Among them, there are warm dark matter (WDM) scenarios, arising, for example, from sterile neutrinos, as well as self-interacting dark matter (SIDM) scenarios , mixed models that combine WDM and SIDM, and Bose–Einstein condensate/fuzzy dark matter scenarios (FDM/BECDM) originating from ultra-light bosons such as axions. The hypothesis that primordial black holes constitute all or most of the dark matter is also revisited in light of the LIGO/Virgo discovery of massive black holes together with very recent constraints from the internal structure of nearby ultra-faint dwarf galaxies. The important role of baryonic physics in the interpretation of various probes of dark matter, especially how it affects the ability to infer dark matter properties from observational diagnostics, is emphasized and reviewed. The effect of baryons blurs, in many cases, the underlying differences in the properties of dark matter halos arising in various dark matter models. Nevertheless, baryons can potentially be a useful tracer of such differences, for instance during the earliest phases of star formation in the lowest mass galaxies. New promising probes which will be delivered by future gravitational wave experiments are discussed, such as the occurrence rate of gravitational wave signals from merging intermediate mass black holes in dwarf galaxies tracing the inner structure of dark halos. Recent observational discoveries and analysis methods, such as the tentative detection of dark subhalos through the analysis of stellar tidal streams in the Milky Way halo, and the prospects of gravitational lensing analysis to directly detect dark substructure down to the relevant small scales, are also illustrated.