A Large Population of High Redshift Galaxy Clusters in the IRAC Shallow Cluster Survey

We have identified 335 galaxy cluster and group candidates spanning 0 < z < 2, using a 4.5 mu m selected sample of galaxies in a 7.25 deg(2) region in the Spitzer/IRAC Shallow Survey. Using full redshift probability distributions for all galaxies, clusters were identified as 3-dimensional overdensities using a wavelet algorithm. To date 12 clusters at z > 1, and over 60 at z < 0.5 have been spectroscopically confirmed. The mean I-[3.6] color for cluster galaxies up to z similar to 1 is well matched by a z(f) = 3 passively evolving model. At z > 1, a wider range of formation histories is needed, but higher formation redshifts (i.e. z(f) >= 4 - 5) are favored for most clusters. The cluster autocorrelation function, measured for the first time out to z = 1.5, is found not to have evolved over the last 10 Gyr, in agreement with the prediction from ACDM. The average mass of the IRAC Shallow Cluster Survey sample, inferred from its clustering, is similar to 10(14)M(circle dot).