Total Infrared Light from Planck Selected Protoclusters

Galaxy protoclusters are structures of galaxies at high redshift that are thought to be the progenitors of massive galaxy clusters in the local Universe. Protoclusters are important to study because they trace both the formation of the cosmic web as overdensities of galaxies as well as how galaxies evolve in clustered environments. A major limiting factor to studying protoclusters is that it is challenging to identify them and to obtain a complete account of their constituent galaxies. To overcome these limitations, we perform a stacking analysis of 211 Planck-selected protocluster candidates from z=2-4. Our analysis involves stacking large images (~10 arcmin) centered on the protoclusters and and studying the total light within a large aperture on the stacked image. We calculate radial profiles and total flux measurements, which we use to fit the spectral energy distribution and quantify the star formation rate and stellar mass. We find the total obscured star formation rates for our protoclusters are large, much larger than summing up the individual detected galaxies suggesting significant star formation from lower luminosity galaxies. We compare our results to similar studies of different protocluster samples. We also compare to an identical analysis on lower redshift (z~1) clusters and find that the protoclusters are much larger than lower redshift galaxy clusters, and consistent with predictions from simulations.