Reversal of fortune: Confirmation of an increasing star formation-density relation in a cluster at z = 1.62

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 (0.4μm< λ_obs < 8μm) and measuring 24μm 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 ∼1700M_⊙ 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 LIR > 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 24μm 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 ∑ ∼ 10 gal Mpc^-2 to ∼25% at ∑ ≳ 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.