We measure the rest-frame colors (dust-corrected), infrared luminosities, star formation rates, and stellar masses of 92 galaxies in a Spitzer-selected cluster at z = 1.62. By fitting spectral energy distributions (SEDs) to 10-band photometry (0.4 μm<λobs < 8 μm) and measuring 24 μm fluxes for the 12 spectroscopically confirmed and 80 photometrically selected members, we discover an exceptionally high level of star formation in the cluster core of ~1700 M sun yr-1 Mpc-2. The cluster galaxies define a strong blue sequence in (U-V) color and span a range in color. We identify 17 members with L IR>1011 L sun, and these IR luminous members follow the same trend of increasing star formation with stellar mass that is observed in the field at z ~ 2. Using rates derived from both the 24 μm imaging and SED fitting, we find that the relative fraction of star-forming members triples from the lowest to highest galaxy density regions; e.g., the IR luminous fraction increases from ~8% at Σ ~ 10 gal Mpc-2 to ~25% at Σ >~ 100 gal Mpc-2. The observed increase is a reversal of the well-documented trend at z < 1 and signals that we have reached the epoch when massive cluster galaxies are still forming a substantial fraction of their stars.
This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion laboratory, California Institute of Technology, under NASA contract 1407. This Letter also includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This work is based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.