Disentangling cosmic-ray and dark matter induced gamma-rays in galaxy clusters?
Résumé
Galaxy clusters are among the best targets for indirect dark matter detection in gamma-rays, despite the large astrophysical background expected from these objects. Detection is now within reach of current observatories (Fermi-LAT or Cerenkov telescopes), however, assessing the origin of this signal might be difficult. We investigate whether the 'number of stacked objects - flux' dependence (log N-log F) could be a signature of the dominant process at stake. We use the CLUMPY code to integrate the signal from decaying/annihilating DM and cosmic rays along the line of sight. We assume the standard NFW profile for the dark matter density and rely on a parametrised emissivity for the cosmic-ray component. In this context, the consequences of stacking are explored using the MCXC meta-catalog of galaxy clusters. The log N-log F power-law behaviour may be a clear signature to disentangle decaying dark matter from cosmic-ray induced gamma-rays (and DM annihilation), contrarily to DM annihilation that has the same slope as cosmic rays. Moreover, the shift between the brightest object and its followers depends on the signal origin, so that the behaviour of the cumulative of the signal does depend on it. We also show that stacking a large number of objects can reinforce the discrimination power of angular dependence studies for a CR or DM decay origin (not for DM annihilation), provided the cluster signal is rescaled by the angular size corresponding its dark matter halo scale radius.