TAPIR Seminar

In the standard cosmological model, small dense dark matter (DM) structures, known as halos, form first and later merge to form larger structures. This hierarchical structure formation scenario predicts abundant substructure (or subhalos) inside of larger halos. Characterizing and understanding the properties of these DM subhalos is crucial to address important questions about e.g. galaxy formation, or the exact role of DM substructure in DM searches. It also allows for detailed probes of the cosmological model at the smallest scales. In this talk, I will review our current knowledge of the DM subhalo population.  I will then discuss the importance that DM subhalos may have for current DM search strategies aimed to detect a DM annihilation signal in gamma rays. On one hand, DM subhalos could represent good targets by themselves: the most massive ones are believed to host the observed Milky Way satellite galaxies (which we know are highly DM-dominated and therefore excellent DM candidates), while those with smaller masses, that may host no stars/gas and be thus completely dark satellites, i.e. with no astrophysical counterparts at other wavelengths, may be also among the best candidates given their distances and masses. On the other hand, as the DM annihilation signal is proportional to the DM density squared, the clumpy distribution of subhalos inside larger halos is expected to boost the DM annihilation flux considerably. I will show that this flux enhancement can only take moderate values in the framework of the concordance cosmology. Yet, it may modify the DM annihilation flux profiles importantly, especially in galaxy clusters. Some of them, indeed, might become as good DM candidates as nearby dwarfs once substructure is properly taken into account.