A Spitzer-selected galaxy cluster at z=1.62

Papovich et al. have found a galaxy (proto-) cluster at z=1.62 by searching for overdensities of objects with red 3.6um-4.5um colors.  Both star-forming and quiescent galaxies at this redshift will have red colors in these passbands, so this is different than the red-sequence selection used by other groups.

Nonetheless, in the author's words, "this is the highest redshift, spectroscopically-confirmed clustering with a strong, well-defined red sequence" (but note that none of the RS galaxies has spectroscopic redshifts).