The flattening of the concentration–mass relation towards low halo masses and its implications for the annihilation signal boost

Miguel A. Sánchez-Conde, Francisco Prada
2014 Monthly notices of the Royal Astronomical Society  
In the standard Cold Dark Matter (CDM) theory for understanding the formation of structure in the universe, there exists a tight connection between the properties of dark matter (DM) haloes, and their formation epochs. Such relation can be expressed in terms of a single key parameter, namely the halo concentration. In this work, we examine the median concentration-mass relation, c(M), at present time, over more than 20 orders of magnitude in halo mass, i.e., from tiny Earth-mass microhalos up
more » ... galaxy clusters. The c(M) model proposed by Prada et al. (2012), which links the halo concentration with the r.m.s. amplitude of matter linear fluctuations, describes remarkably well all the available N-body simulation data down to ~10^(-6) Msun microhalos. A clear fattening of the halo concentration-mass relation towards smaller masses is observed, that excludes the commonly adopted power-law c(M) models, and stands as a natural prediction for the CDM paradigm. We provide a parametrization for the c(M) relation that works accurately for all halo masses. This feature in the c(M) relation at low masses has decisive consequences e.g. for gamma-ray DM searches, as it implies more modest boosts of the DM annihilation flux due to substructure, i.e., ~35 for galaxy clusters and ~15 for galaxies like our own, as compared to those huge values adopted in the literature that rely on such power-law c(M) extrapolations. We provide a parametrization of the boosts that can be safely used for dwarfs to galaxy cluster-size halos.
doi:10.1093/mnras/stu1014 fatcat:bl2urp4mxvh2peehdm4lzxseya