Simulating the dark matter decay signal from the Perseus Galaxy Cluster.

Abstract

the C-EAGLE simulations of galaxy clusters to predict the flux, width, and shape of a dark matter decay line, paying particular attention to the unexplained 3.55keV line detected in the spectra of some galaxies and clusters, and the upcoming XRISM X-ray observatory mission. We show that the line width in C-EAGLE clusters similar to Perseus is typically [600–800]km s-1, and therefore narrower than the amplitude of the velocity dispersion of galaxies in the cluster. Halos that are significantly disturbed can, however, exhibit galaxy velocity dispersions higher than 1000km s-1, and in this case will show a large difference between the line profiles of on- and offcenter observations. We show that the line profile is likely to be slightly asymmetric, but still well approximated by a Gaussian at the 10% level, and that the halo asymmetry can lead to fluxes that vary by a factor of two. In summary, we predict that, if the previously reported 3.55keV line detections do originate from dark matter decay, the XRISM mission will detect a line with a roughly Gaussian profile at a rest-frame energy of 3.55keV, with a width >600 km s-1and flux approximately in the range [4–9] ´ 10-8 counts s-1 cm-2.