  The potential for Planck to detect clusters of dusty, star-forming galaxies
at z greater than 1 is tested by examining the Herschel-SPIRE images of Planck
Early Release Compact Source Catalog (ERCSC) sources lying in fields observed
by the HerMES survey. Of the 16 Planck sources that lie in the roughly 90 sq.
deg. examined, we find that twelve are associated with single bright Herschel
sources. The remaining four are associated with overdensities of Herschel
sources, making them candidate clusters of dusty, starforming galaxies. We use
complementary optical and NIR data for these clumps to test this idea, and find
evidence for the presence of galaxy clusters in all four cases. We use
photometric redshifts and red sequence galaxies to estimate the redshifts of
these clusters, finding that they range from 0.8 to 2.3. These redshifts imply
that the Herschel sources in these clusters, which contribute to the detected
Planck flux, are forming stars very rapidly, with typical total cluster star
formation rates greater than 1000Msun per yr. The high redshift clusters
discovered in these observations are used to constrain the epoch of cluster
galaxy formation, finding that the galaxies in our clusters are 1 to 1.5 Gy old
at z about 1 to 2. Prospects for the discovery of further clusters of dusty
galaxies are discussed, using not only all sky Planck surveys, but also deeper,
smaller area, Herschel surveys.
