Questioning Planck-selected star-forming high-redshift galaxy
  protoclusters and their fate
  About 2100 star-forming galaxy protocluster candidates at z=1-4 were
identified at submillimeter (sub-mm) wavelengths in the Planck all sky survey.
Follow-up spectroscopic observations of a few candidates have confirmed the
presence of galaxy overdensities with large star-formation rates. In this work,
we use state-of-the-art hydrodynamical simulations to investigate whether the
Planck high-z sub-mm sources (PHz) are progenitors of massive clusters at z=0.
To match the PHz sources with simulated halos, we select the most star-forming
(SF) halos from z=3 to z=1.3 in the IllustrisTNG300 simulation. At each
redshift, the total star formation rate (SFR) of the simulated protocluster
candidates is computed from the SFR of all the galaxies within an aperture
corresponding to the Planck beam size, including those along the line-of-sight.
The simulations reproduce the Planck derived SFRs as the sum of both, the SFR
of at least one of the most SF high-z halo, and the average contribution from
SF sources along the line-of-sight. Focusing on the spectroscopically confirmed
PHz protoclusters, we compare the observed properties of their galaxy members
with those in the most SF simulated halos. We find a good agreement in the
stellar mass and SFR distributions, and in the galaxy number counts, but the
SFR-stellar mass relation of the simulated galaxies tend to be shifted to lower
SFRs with respect to the observed one. Based on the estimated final masses of
the simulated halos, we infer that between 63% and 72% of the Planck selected
protoclusters will evolve into massive galaxy clusters by z=0. We confirm the
efficiency of Planck to select star-forming protoclusters at Cosmic Noon with
the simulations, and provide a new criterion for selecting the most massive
cluster progenitors at high-z, using observables like the number of galaxy
members and their SFR distribution.
