Cosmic spring of large-scale structures: Spizter and the search for z ∼ 2 highly star-forming structures following Planck and Herschel

Galaxies are beacons in the Universe that allow us to understand the evolution of the distribution of matter in all its forms in the Universe. The study of galaxies at different cosmic epochs allows us to understand how they are organized at cosmological scales (superior to inter-galaxy distance) but also how they form, and in particular form their stars At our cosmic time, galaxies in the densest environments (groups, clusters) exhibit very different properties from other galaxies. This bimodality - between elliptic, massive, old galaxies that form few stars in dense environments on the one hand, and spiral galaxies, younger and experimenting intense stellar formation in less dense environments on the other - reflects different evolution and formation mechanisms. The study of galaxies in local clusters seems to indicate that they formed the majority of their stars in a short colossal episode of stellar formation (∼500-1000 M per year) at redshifts z ≥ 2, before evolving passively. However, few such structures have been observed during such a phase to this day, which is consequently still poorly constrained. In order to construct such a sample, a selection directly targeting the star formation using the Planck satellite made it possible to identify more than 2,000 candidates based on their submillimetric colors. A follow-up with the Herschel space telescope on 228 candidates revealed red sources, having their peak emission between 350 and 500 microns, present in significant excess compared to reference surveys. This is compatible with significant overdensities of galaxies intensely forming stars (several hundred solar masses per year), and located at redshifts z ≥ 2. This thesis work presents a follow-up of part of this sample using the Spitzer Space Telescope, which results in the SPHerIC (Spitzer Planck Herschel Infrared Clusters) sample comprising 84 candidates. The data collected by the Spitzer IRAC instrument (observing at 3.6 and 4.5 microns) allowed to identify significant overdensities of galaxies compatible with z> 1.5, at an angular resolution 10 times better than that of Herschel. These overdensities are also angularly associated with the star formation identified by Herschel, and present coherent colors. A large proportion of these overdensities are also spatially extended (> 2 '), pointing to structures still in formation. Finally, few structures with such density contrasts are present in other surveys, confirming the exceptionality of the structures identified by Planck and Herschel. These indications lead us to suppose that the SPHerIC sample consists of clusters and protoclusters of galaxies located at z> 1.5 - 2 during a major assembly phase of their stellar mass. These candidates, however, need to be confirmed before their physical properties (redshift, mass, gas content, etc.) can be estimated, and thus constrain the evolution mechanisms of galaxies in dense environments. A follow-up has therefore been initiated for this purpose, in the millimeter and near infrared domains. Observations with the 30 m antenna of the IRAM were carried out, and confirmed 3 candidates for redshifts z ∼ 2. Data were also obtained with the ALMA interferometer, which points to a multiple origin of the star formation. Data have been obtained in the near infrared using ground-based telescopes, and will allow to better constrain the properties of these objects, in particular to prepare a spectroscopic follow-up. (author)