Protoclusters of galaxies: from Planck to the Euclid and JWST era

Clusters of galaxies are key structures for our understanding of galaxy
evolution physics in denser environments, for constraining the structure
formation scenario and some cosmological parameters independantly of
other techniques like CMB. Despite the difficulties to observe, detect
and model them, there are successes in studying and using galaxy
clusters. In the recent years, many hight-redshift galaxy clusters (z>1)
were detected as well as many high-redshift protoclusters (z>1.5),
progenitors of todays’s clusters. These objects help answering crucial
questions like how and when the clusters formed stars ? In a
synchroneous way ? What is the fate of the gas in clusters ?

After a review of the current status of protoclusters search and
properties and the latest results, I will focus on the original program
we are performing with Planck, Herschel, Spitzer, IRAM, ALMA and other
facilities.

We selected an original sample of about 2000 highly star-forming
structures candidates in Planck, deep in the Cosmic Infrared Background.
Selection was not done in SZ, but by colors of the redshifted peak of
thermal far-infrared emission of galaxies. We observed about 200 of them
with Herschel/SPIRE, about 80 of them with Spitzer/IRAC, and about a
dozen in the near-infrared and millimeter ranges. We have a few redshift
confirmations, and I will highlight our main findings, work in progress,
and perspectives of the SPHerIC subsample (Spitzer, Planck, Herschel
infrared clusters).

A colleague said wisely about high-redshift clusters and protoclusters
in a review talk, « we need more than one object at a time. » Euclid and
JWST will make evolve this field (and other) after 2021 with increasing
statistics and a sharp, detailed view of these structures at the
« cosmic noon » epoch and earlier.