IDCS J1426.5+3508: DISCOVERY OF A MASSIVE, INFRARED-SELECTED GALAXY CLUSTER AT z=1.75

We report the discovery of an IR-selected massive galaxy cluster in the IRAC Deep Cluster Survey (IDCS). We present new data from the Hubble Space Telescope and the W. M. Keck Observatory that spectroscopically confirm IDCS J1426.5+3508 at z = 1.75. Moreover, the cluster is detected in archival Chandra data as an extended X-ray source, comprising 53 counts after the removal of point sources. We calculate an X-ray luminosity of L0.5-2 keV = (5.4 +/- 1.2) x 10(44) erg s(-1) within r = 60 arcsec (similar to 1 Mpc diameter), which implies M-200,M- Lx = (5.3 +/- 1.6) x 10(14) M-circle dot. IDCS J1426.5+3508 appears to be an exceptionally massive cluster for its redshift.