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Le printemps cosmique des grandes structures : Spitzer et la recherche de structures à z ~ 2 à haut taux de formation stellaire dans le sillage de Planck et Herschel.

Abstract : Galaxies are beacons in the Universe that allow us to understand the evolution of the distribution matter in all its forms. The study of galaxies at different epochs helps to understand how they organize at large scales (greater than inter-galaxies distance) but also how they formed, and formed their stars.At our cosmic epoch, galaxies that reside in the densest environments (clusters, groups) have very different properties compared to galaxies residing in less dense environments. This bimodality between 1) elliptical galaxies, massive, old and forming little stars in dense environments on the one hand, and 2) of spiral galaxies, younger and experimenting intense star formation in less dense environments indicates different evolutionary mechanisms and formation mechanisms.The study of galaxies in clusters reveals that they probably experimented intense star formation at redshifts z ~ 2, and points to a synchronous episode of star formation in the galaxies in the cluster, and of colossal proportions (~ 500 solar masses per year, to be compared with the average rate of star formation observed in the local Universe in the order of ~ 1-10 solar masses per year). But this phase still lack a direct observational conclusion, although recent observations in this direction.One possible way to search for these objects is to try to detect their emission in the far infrared, which traces directly star formation. This is what has been achieved with the Planck satellite. From Planck / HFI data, a team in collaboration with us extracted 2151 cluster candidates experimenting an intense star formation phase. A follow-up of 228 candidates was made with the space telescope Herschel / SPIRE, and revealed overdensities of red sources, compatible with a redshift distribution peaking around z ~ 2, and star formation rates of approximately 700 masses solar year.To better constrain the redshift of these candidates, study their contents in terms of stars, another follow-up on 80 candidates was conducted using the IRAC instrument on the Spitzer Space Telescope. My work focuses on the analysis and interpretation of such data.The wavelengths of the IRAC instrument (3.6 and 4.5 microns) are indeed tailored to detect a characteristic peak emission of stellar populations, to estimate the redshift and the stellar mass.My work revealed overdensities of red IRAC sources (z> 1.3) at the positions of the red SPIRE sources (z ~ 2 ~ SFR), compatible with clusters or proto-clusters in an intense star formation phase. Estimates of photometric redshifts and stellar mass show that these objects are compatible with the progenitors of local clusters.These candidates, however, require confirmation, especially with obtaining spectroscopic redshifts. This work has already begun, and two candidates have already been confirmed at redshifts of 2.15 and 2.36 using the 30m / IRAM. Data obtained with the ALMA interferometer and NOEMA revealed that the SPIRE emission originates in some cases from several galaxies.These initial results are encouraging, but a study at other wavelengths (near infrared) is also needed to better constrain the content of our mass objects, and their star formation history. The data is already available on part of the smple, and analysis has begun.
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Submitted on : Monday, March 20, 2017 - 3:43:12 PM
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Clément Martinache. Le printemps cosmique des grandes structures : Spitzer et la recherche de structures à z ~ 2 à haut taux de formation stellaire dans le sillage de Planck et Herschel.. Cosmologie et astrophysique extra-galactique [astro-ph.CO]. Université Paris-Saclay, 2016. Français. ⟨NNT : 2016SACLS300⟩. ⟨tel-01492799⟩



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