Being the most massive collapsed and bound structures in the
Universe, galaxy clusters have a variety of cosmological applications.
Massive galaxy clusters at high redshift are expected to be increasingly
rare, hence their abundance is an extremely sensitive indicator of the
background cosmology. While a variety of cluster detection techniques
exist, infrared observations are proving to be particularly well suited
for the detection of the rarest clusters, as the apparent infrared
magnitude of cluster galaxies is almost independent of redshift. I
report the discovery of one such rare cluster in the Spitzer/IRAC Deep
Cluster Survey, spectroscopically confirmed at z = 1.75. Mass estimation
has been possible thanks to X-ray emission and SZ distortion. While this
object is certainly extreme it does not seem to be incompatible with the
currently favored cosmological model. The cluster however also displays
a giant arc, produced by gravitational lensing over a background source.
The very existence of this feature might be very difficult to explain
within the concordance cosmology.