Searching for Decaying Axionlike Dark Matter from Clusters of Galaxies

We constrain the lifetime of radiatively decaying dark matter in clusters of galaxies inspired by generic Kaluza-Klein axions, which have been invoked as a possible explanation for the solar coronal x-ray emission. These particles can be produced inside stars and remain confined by the gravitational potential of clusters. By analyzing x-ray observations of merging clusters, where gravitational lensing observations have identified massive, baryon poor structures, we derive the first cosmological lifetime constraint on this kind of particles of $\tau \gtrsim {10}^{23}\sec$.

Figure 1

The reconstructed quiet Sun x-ray spectrum (upper curve) [25] and the expected flux from decaying massive axions of the Kaluza-Klein type (lower curve) [1].

Figure 2

The x-ray image of Abell 520 (above) and the Bullet Cluster (below) overlaid the gravitational potential from weak gravitational lensing (in units of $\kappa$, Bullet Cluster contours from 16). The dark matter blob regions are the white leftmost circles, and the reference regions are the rightmost circles.

Figure 3

The observed spectrum of the blob region (squares) of Abell 520 with the fitted “basis model” (solid, reduced ${\chi }^2\approx 1$) and the spectrum of the reference region (triangles).