Sujet These Doctorale 2010 LE FEVRE Angl

Eharmitt

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• Publié par: Shoun
• Nombre de lectures: 13
• Langue: English

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PhD thesis at Laboratoire d’Astrophysique de Marseille Université de Provence, Aix-Marseille I (2010-2011) PhD topic : The first galaxies and mass assembly in galaxies 1 to 4 billion years after the Big-Bang  Keywords : Formation and evolution of galaxies and large scale structures.  PhD thesis advisor : Olivier Le Fèvre, Director LAM, [e-mail]  Location: LAM, Technopole de Château Gombert, Marseille, France,http://www.oamp.fr/lam Summary of the PhD thesis : The currently favored scenario for the formation and evolution of galaxies is based on a hierarchical assembly of mass, with smaller structures merging along time to build more massive structures. There are still many unknowns in this scenario, because observations at early epochs are difficult and therefore incomplete. In particular, the epoch when the first galaxies were assembled is still out of reach of current observational capabilities, and the critical epoch when most of the mass seem to have been assembled, between redshifts 1 and 5, is still poorly observed. Making observations in the infrared should enable to find the first galaxies at the reionization epoch, to follow the star formation history, and to understand how stellar mass has assembled along cosmic time. Until today it has been very difficult to obtain very deep near-infrared images and the spectroscopic redshifts of galaxies in a large volume of the Universe. This situation is about to change with the new 4m VISTA IR telescope of the European Southern Observatory in Chile, and a new Large Program with the VLT-VIMOS. The thesis advisor at LAM is one of the principal investigators (PI) of the Ultra-VISTA survey, a European collaboration which has been awarded an outstanding total of 1800h of observations with VISTA, 25% of the total telescope time over 5 years, starting end 2009, and is the PI of the 600h Large Program to obtain spectra of 10,000 galaxies with VIMOS. These surveys will enable to obtain images in YJHK bands of 1.5 square degrees at a depth of K AB =25.6, and spectra to I AB =24.75. These leading surveys will enable: (1) to identify a significant sample of the first galaxies after reionisation at redshifts up to z~10, and (2) to follow the mass assembly at the peak of star formation, from z~5 to z~1. The PhD work will aim in a first part to identify the most distant galaxies in the Ultra-VISTA images. A detailed analysis of their physical properties will follow, in particular to measure the stellar population content. Spectroscopic follow-up will be performed in search for the long sought-for Population III stars indicating a primordial stellar population corresponding to “first light” in the Universe. These first galaxies will place strong constraints on the epoch of reionisation. In a second part, the accurate measurement of the spectrophotometric and spectral properties of galaxies observed at the peak of star formation and mass build-up will enable to obtain important physical informations on their age, star formation rate, total stellar mass, or metallicity, from a direct fit with stellar population synthesis models. The global properties will be described using well defined statistical descriptors like the luminosity function, mass function, correlation function, merging rate. The thesis work will aim to bring new elements to the fundamental questions related to the mass assembly along cosmic time and its relationship with the distribution of dark matter halos in the cosmic web of large scale structures using HOD models. One of the main goals is to identify the major phases of the assembly of galaxies of different types, to quantify the contribution of different physical processes (merging, feedback, cold accretion, quenching,…) and to propose a coherent scenario for the evolution of galaxies. The expertise acquired throughout the thesis work will place the student in a unique position to participate to the next generation of major investigations with the James Webb Space Telescope in space (2014+), or with the future Extremely Large Telescopes on the ground.

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