IDCS J1433.2+3306: AN INFRARED-SELECTED GALAXY CLUSTER AT z=1.89

We report the discovery of an IR-selected galaxy cluster in the IRAC Distant Cluster Survey (IDCS). New data from the Hubble Space Telescope spectroscopically confirm IDCS J1433.2+3306 at z = 1.89 with robust spectroscopic redshifts for seven members, two of which are based on the 4000 angstrom break. Detected emission lines such as [O II] and H beta indicate star formation rates of greater than or similar to 20 M-circle dot yr(-1) for three galaxies within a 500 kpc projected radius of the cluster center. The cluster exhibits a red sequence with a scatter and color indicative of a formation redshift z(f) greater than or similar to 3.5. The stellar age of the early-type galaxy population is approximately consistent with those of clusters at lower redshift (1 < z < 1.5) suggesting that clusters at these redshifts are experiencing ongoing or increasing star formation.