# Simulating the dark matter decay signal from the Perseus galaxy cluster

## TL;DR

This paper uses simulations to predict the characteristics of a dark matter decay signal in the Perseus galaxy cluster, focusing on the 3.55 keV line and its detectability by the XRISM mission.

## Contribution

It provides detailed predictions of the dark matter decay line profile, width, and flux in galaxy clusters, especially considering halo disturbances and asymmetries.

## Key findings

- Line width in similar clusters is 600-800 km/s.
- Halo disturbances can cause velocity dispersions over 1000 km/s.
- Predicted line flux is 4-9 x 10^{-8} counts/sec/cm^2.

## 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]$\mathrm{kms^{-1}}$, 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 $1000\mathrm{kms^{-1}}$, 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 $>600\mathrm{kms^{-1}}$ and flux approximately in the range $[4-9]\times10^{-8}\mathrm{counts/sec/cm^{2}}$.