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[en] The epoch of cosmic reionization that ended the so-called cosmic 'Dark-Ages' and during which the first stars and galaxies formed is a landmark event in the history of the early Universe. High-redshift quasars, as background sources, are powerful tools to constrain the cosmic reionization since they provide reliable information on the intergalactic medium state during this period. My PhD work is centered on the search for high-redshift quasars in the Canada France High-z Quasar Survey in the Near Infrared (CFHQSIR). The main scientific objective of this CFHT Large Program is to search for quasars at redshift z ∼ 7 with near-infrared images (Y -band) of the CFHTLS Wide fields acquired with the CFHT WIRCam camera. Firstly, I carried out the photometric calibration of the CFHQSIR images and performed a detailed analysis of the CFHQSIR data by studying their quality, as well as their noise properties and their depths. Secondly, I computed the number of high-redshift quasars that could be detected with CFHQSIR and the corresponding constraints which could be put on the z ∼ 7 quasar luminosity function. Then, I proceeded to the identification of quasar candidates among the many thousands of sources in the 130 deg2 covered by CFHQSIR. A first selection was made based on a double analysis of our near infrared images (CFHQSIR) and optical data from the CFHTLS. Photometric follow-up observations of the candidates and application of color criteria revealed about fifty objects, of which around twenty were chosen to be spectroscopically observed. The observations of nine of them were not conclusive. Since this spectroscopic follow-up is not yet completed, the exact nature of the remaining sources is still not known and will be fixed in the next months. To finish, I focused my work on bayesian statistics in order to complete and consolidate my selection procedure. I computed the probability of a source to be a high-redshift quasar by combining quasars and brown dwarfs population models. My candidates were finally classified according to their probability to be a high-redshift quasar, verifying that the majority of the most likely candidates were selected for spectroscopic observations. (author)
[fr]
L'epoque de la reionisation marquant la fin des 'Ages Sombres' et durant laquelle les premieres etoiles et galaxies se sont formees, represente un evenement majeur dans l'histoire de l'Univers. Les quasars a grand decalage spectral (redshift), en tant que sources d'arriere-plan, fournissent de precieuses informations concernant l'etat d'ionisation du milieu intergalactique pendant la reionisation et constituent de puissants outils pour contraindre cette periode. J'ai consacre mon travail de these a la recherche de quasars a haut redshift dans le releve Canada France High-z Quasar Survey in the Near Infrared (CFHQSIR). L'objectif principal de ce programme est de decouvrir des quasars de redshift z ∼ 7 dans les champs larges du CFHTLS (CFHTLS Wide) en utilisant des images realisees dans le proche infrarouge (filtre Y) avec la camera WIRCam installee au foyer du CFHT. J'ai dans un premier temps effectue la calibration photometrique de l'ensemble des donnees de CFHQSIR et etudie leur qualite, ainsi que leurs proprietes de bruit et leurs profondeurs. Dans un deuxieme temps, j'ai calcule le nombre de quasars qu'il serait possible de detecter avec CFHQSIR et en ai deduit les contraintes envisageables sur la fonction de luminosite des quasars a z ∼ 7. J'ai ensuite procede a l'identification de candidats quasars parmi les dizaines de milliers de sources que comptent les 130 deg2 couvert par CFHQSIR. Un suivi photometrique des candidats ainsi que l'application de criteres en couleurs ont permis de reveler une cinquantaine d'objets, dont une vingtaine a ete selectionnee pour des observations spectroscopiques. Les observations de neuf objets ont deja ete realisees: celles-ci ne se sont pas averees concluantes. La totalite des observations n'ayant pas encore ete effectuee, la nature exacte des sources restantes demeure inconnue et ne pourra etre fixee que dans les prochains mois. Pour finir, j'ai focalise la derniere partie de ma these sur l'etude de modeles statistiques bayesiens afin de completer et consolider ma procedure de selection. En combinant deux modeles de population de quasars et de naines brunes, j'ai calcule la probabilite qu'une source soit un quasar a haut redshift. Mes candidats ont ensuite ete classes selon leur probabilite d'etre un quasar. Cela m'a finalement permis de verifier que la majorite des objets retenus pour des observations spectroscopiques etaient effectivement les candidats les plus probables. (auteur)Original Title
A la recherche de quasars a grand decalage spectral dans le sondage CFHQSIR
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30 Nov 2017; 257 p; 171 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; These docteur, Discipline: Sciences de la Terre et de l'Univers, Specialite: Astrophysique et Cosmologie
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