Simulating the dark matter decay signal from the Perseus galaxy cluster

Abstract

The nearby Perseus galaxy cluster is a key target for indirect detection searches for decaying dark matter. We use 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 3.55keV 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]$\mathrm{km}{\mathrm{s}}^{-1}$, and therefore narrower than the amplitude of the velocity dispersion of galaxies in the cluster. Haloes that are significantly disturbed can, however, exhibit galaxy velocity dispersions higher than $1000\mathrm{km}{\mathrm{s}}^{-1}$, and in this case will show a large difference between the line profiles of on- and off-center 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 3.55keV 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 3.55keV, with a width $>600\mathrm{km}{\mathrm{s}}^{-1}$ and flux approximately in the range $[4-9]\times 10^{-8}counts/sec/c{\mathrm{m}}^2$.

arXiv comment6 pages and 3 figures, plus 5 pages and 6 figures in supplemental material. Accepted for publication in ApJL

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• Long-Exposure NuSTAR Constraints on Decaying Dark Matter in the Galactic Halo
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