2012ApJ...749L..43C

We have discovered a 2.5 Mpc (projected) long filament of infrared-bright galaxies connecting two of the three ∼5x10¹⁴ M_☉ clusters making up the RCS 2319+00 supercluster at z = 0.9. The filament is revealed in a deep Herschel Spectral and Photometric Imaging REceiver (SPIRE) map that shows 250-500 µm emission associated with a spectroscopically identified filament of galaxies spanning two X-ray bright cluster cores. We estimate that the total (8-1000 µm) infrared luminosity of the filament is L_IR ≃ 5x10¹² L_☉, which, if due to star formation alone, corresponds to a total SFR ≃ 900 M_☉/yr. We are witnessing the scene of the buildup of a >10¹⁵ M_☉ cluster of galaxies, seen prior to the merging of three massive components, each of which already contains a population of red, passive galaxies that formed at z > 2. The infrared filament demonstrates that significant stellar mass assembly is taking place in the moderate density, dynamically active circumcluster environments of the most massive clusters at high redshift, and this activity is concomitant with the hierarchical buildup of large-scale structure.