Mergerträds

Mergerträds, a term originating from German, translates literally to "merger trees." In the context of cosmology and astrophysics, mergerträds are a theoretical construct used to describe the hierarchical formation of dark matter halos. These trees visually represent the process by which smaller dark matter halos merge over cosmic time to form larger, more massive ones. The branching structure of a mergerträd illustrates these mergers, with the root of the tree representing a present-day massive halo and its branches extending back in time to smaller progenitor halos that eventually merged to create it.

The construction of mergerträds typically relies on large-scale cosmological simulations. These simulations track the evolution of dark matter particles in a virtual universe, identifying halos at different epochs. By tracing the ancestry of particles within a halo at a later time, astronomers can identify which halos existed at earlier times and subsequently merged to form the larger halo. This process allows for the study of halo assembly histories, accretion rates, and the statistical properties of dark matter structures. Mergerträds are fundamental tools for understanding the growth of cosmic structures, from dwarf galaxies to galaxy clusters, and are crucial for comparing theoretical predictions with observational data. They help explain why larger halos are generally found to have more complex internal structures and histories of mergers compared to smaller, less evolved halos.