Galaxy Cluster Contribution to the Diffuse Extragalactic Ultraviolet
  Background
  The diffuse ultraviolet background radiation has been mapped over most of the
sky with 2\arcmin \ resolution using data from the \textit{GALEX} survey. We
utilize this map to study the correlation between the UV background and
clusters of galaxies discovered via the Sunyaev-Zeldovich effect in the
\textit{Planck} survey. We use only high Galactic latitude ($|b| > 60^{\circ}
$) galaxy clusters to avoid contamination by Galactic foregrounds, and we only
analyze clusters with a measured redshift. This leaves us with a sample of 142
clusters over the redshift range $0.02 \leq z \leq 0.72$, which we further
subdivide into four redshift bins. In analysing our stacked samples binned by
redshift, we find evidence for a central excess of UV background light compared
to local backgrounds for clusters with $z<0.3$. We then stacked these $z<0.3$
clusters to find a statistically significant excess of $12 \pm 2.3$ photon
cm$^{-2}$ s${-1}$ sr$^{-1}$ \AA $^{-1}$ \ over the median of $\sim 380$ photon
cm$^{-2}$ s${-1}$ sr$^{-1}$ \AA $^{-1}$ \ measured around random blank fields.
We measure the stacked radial profile of these clusters, and find that the
excess UV radiation decays to the level of the background at a radius of $\sim
1$ Mpc, roughly consistent with the maximum radial extent of the clusters.
Analysis of possible physical processes contributing to the excess UV
brightness indicates that non-thermal emission from relativistic electrons in
the intracluster medium and faint, unresolved UV emission from cluster member
galaxies and intracluster light are likely the dominant contributors.
