Presentation #139.04 in the session Galaxy Clusters/Large Scale Structure, Cosmic Distance — iPoster Session.
Galaxies residing in present-day galaxy clusters are thought to have completed their mass assembly early and have since been evolving passively. However, the details of their formation histories remain uncertain. Existing studies are limited to the brightest constituents in these galaxy protoclusters which may not represent the overall population. To study the total stellar mass and star formation rate within protoclusters, including the contribution from faint undetected galaxies, we perform a stacking analysis of 211 Planck-selected protoclusters from z=2-4. We stack images from Herschel SPIRE and WISE to measure the angular size and the spectral energy distribution (SED) of the integrated light from the protocluster galaxies. In all probed bands, we find that protoclusters subtend a FWHM of 6' (3 Mpc physical scale at z=2), considerably more extended than z~1 galaxy clusters stacked using the same technique. Using cosmological simulations, we correct the measured fluxes for the incidence of multiple structures along the line-of-sight within the protocluster sample. We then fit the SED to derive the best-fit stellar mass and star formation rate estimates. We find that our stacked protoclusters have on average around two times more star formation and four times as much stellar mass than summing up the contributions from individually detected galaxies in well-studied protoclusters. This suggests that much of the mass and star-formation within protoclusters might be dominated by lower mass constituent galaxies.