2010ApJ...719L.126T

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<λ_obs< 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_☉/yr/Mpc2. 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_☉, 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/Mpc2 to ∼25% at Σ ≳ 100 gal/Mpc2. 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.