Institute for Advanced Study Astrophysics Seminar

We have undertaken a novel census of red sources identified by their rest-frame far infrared colors using Planck and Herschel telescopes, and not by the Sunyaev-Z'eldovich effect (SZE). The vast majority of sources are high-redshift galaxy overdensity candidates. These structures have high total measured star formation rates of ~1000 solar masses per year and show tentative evidence for low molecular gas masses, as expected for a population nearing the end of an active epoch of star formation. On the other hand, a small minority of sources are dusty star forming galaxies (DSFGs) which are individually-detected by Planck as a result of strong lensing by massive foreground structures. We obtained Hubble Space Telescope WFC3-IR imaging in the fields of six of these classical giant arcs. We focus on one cluster lens that stands out for its a high mass and high dark-matter-density, while at the same time its low X-ray luminosity unremarkable Planck SZE decrement. We discuss the possibility that this double cluster may be intercepted in a relatively rare "pre-core" initial infall state. As a result of its unusual physical properties, this cluster will be observed in guaranteed time using the JWST.