  Ultra-high-energy cosmic rays (UHECRs) are known to come from outside of our
Galaxy, but their origin still remains unknown. The Telescope Array (TA)
experiment recently identified a high concentration in the arrival directions
of UHECRs with energies above $5.7 \times 10^{19} eV$, called hotspot. We here
report the presence of filaments of galaxies, connected to the Virgo Cluster,
on the sky around the hotspot, and a statistically significant correlation
between hotspot events and the filaments. With 5-year TA data, the maximum
significance of binomial statistics for the correlation is estimated to be 6.1
$\sigma$ at correlation angle 3.4 degree. The probability that the above
significance appears by chance is $\sim 2.0 \times 10^{-8}$ (5.6 $\sigma$).
Based on this finding, we suggest a model for the origin of TA hotspot UHECRs;
they are produced at sources in the Virgo Cluster, and escape to and propagate
along filaments, before they are scattered toward us. This picture requires the
filament magnetic fields of strength $\gtrsim 20$ nG, which need to be
confirmed in future observations.
