The XMM Cluster Survey: new evidence for the 3.5 keV feature in clusters is inconsistent with a dark matter origin

Abstract

There have been several reports of a detection of an unexplained excess of X-ray emission at $\simeq$ 3.5 keV in astrophysical systems. One interpretation of this excess is the decay of sterile neutrino dark matter. The most influential study to date analysed 73 clusters observed by the XMM-Newton satellite. We explore evidence for a $\simeq$ 3.5 keV excess in the XMM-PN spectra of 117 redMaPPer galaxy clusters ($0.1<z<0.6$). In our analysis of individual spectra, we identify three systems with an excess of flux at $\simeq$ 3.5 keV. In one case (XCS J0003.3+0204) this excess may result from a discrete emission line. None of these systems are the most dark matter dominated in our sample. We group the remaining 114 clusters into four temperature ($T_{\mathrm{X}}$) bins to search for an increase in $\simeq$ 3.5 keV flux excess with $T_{\mathrm{X}}$ - a reliable tracer of halo mass. However, we do not find evidence of a significant excess in flux at $\simeq$ 3.5 keV in any $T_{\mathrm{X}}$ bins. To maximise sensitivity to a potentially weak dark matter decay feature at $\simeq$ 3.5 keV, we jointly fit 114 clusters. Again, no significant excess is found at $\simeq$ 3.5 keV. We estimate the upper limit of an undetected emission line at $\simeq$ 3.5 keV to be $2.41\times 10^{-6}$ photons cm${}^{-2}$ s${}^{-1}$, corresponding to a mixing angle of ${\sin }^2(2\theta )=4.4\times 10^{-11}$, lower than previous estimates from cluster studies. We conclude that a flux excess at $\simeq$ 3.5 keV is not a ubiquitous feature in clusters and therefore unlikely to originate from sterile neutrino dark matter decay.

17 pages, 14 figures. Accepted for publication in MNRAS

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• A Search for the 3.5 keV Line from the Milky Way's Dark Matter Halo with HaloSat
• Modelling Heavy Neutral Leptons in Accelerator Beamlines
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• Atomic Size Dark Matter Pearls, Electron Signal
• Phasing out of Darkness: From Sterile Neutrino Dark Matter to Neutrino Masses via Time-Dependent Mixing
• Searching for Particle Dark Matter with eROSITA Early Data
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