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Impact Des Fusions Majeures Sur L'evolution Des Galaxies Spirales Et Impact des fusions majeures sur l’evolution des galaxies spirales et naines Sylvain Fouquet To cite this version: Sylvain Fouquet. Impact des fusions majeures sur l’evolution des galaxies spirales et naines. Astro- physique galactique [astro-ph.GA]. Université Paris-Diderot - Paris VII, 2013. Français. tel-00975096 HAL Id: tel-00975096 https://tel.archives-ouvertes.fr/tel-00975096 Submitted on 7 Apr 2014 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. UNIVERSITÉ PARIS. DIDEROT (Paris 7) École doctorale d’Astronomie et d’Astrophysique d’Île de France Observatoire de Paris-Meudon Laboratoire Galaxies, Étoiles, Physique et Instrumentation - UMR 8111 THÈSE Présentée en vue de l’obtention du titre de : Docteur en astronomie par Sylvain FOUQUET Impact des fusions majeures sur l’évolution des galaxies spirales et naines Thèse dirigée par François Hammer Soutenue le 24 juin 2013 M. Didier Pelat, Président M. François Hammer, Directeur de thèse M. Pavel Kroupa, Rapporteur M. Rodrigo Ibata, Rapporteur Mme Simona Mei, Examinateur M. Albert Bosma, Examinateur Remerciements La thèse comme la plupart de ce que l’on accomplit n’est pas une oeuvre personnelle mais le résultat d’une collaboration. Mes collègues proches mais aussi d’autres personnes ont eu un impact sur le travail de ma thèse de manière plus ou moins directe. C’est toutes ces personnes qui ont compté pour moi durant les quatre annnées de ma thèse que j’aimerais remercier ici. Je souhaiterais tout d’abord remercier les membres de mon jury de thèse qui ont convenu que mon travail était digne d’intérêt et que je méritai le grade de Docteur. Chacun a compté à un degrée divers pour mon travail de thèse. Pavel Kroupa, avec son travail sur le VPOS et les galaxies naines, m’a ouvert la voie pour mon travail sur le Groupe Local. Rodrigo Ibata et sa découverte du plan de galaxies naines autour de M31 a permis à mon travail de thèse de prendre de l’ampleur en étudiant le système de satellite de M31. Didier Pelat a été un des mes professeurs durant ma deuxième année de Master et m’a inculqué les bases de l’outil statistique qui m’ont ensuite servi durant ma thèse. Une rapide discussion avec Albert Bosma sur la science lors d’une conférence m’a conforté dans mon envie de faire de la recherche. Enfin, Simona Mei en tant que représentante de Paris VII, l’Université où j’ai étudié deux ans et fait trois ans de monitorat, m’a aidé dans la mise en place de ma soutenance. Je remercierais ensuite ceux qui ont contribué à ma formation. En premier, ma pensée va à mon directeur de thèse. Souvent présent, François Hammer est un directeur de thèse exigeant mais juste. Avec lui, on ne reste pas cantonné à un domaine très spécifique de la science ; ses idées obligent à manipuler différents phénomènes physiques, ce qui est très formateur. Bon pédagogue, il est aussi un bon professeur pour apprendre la démarche scientifique : l’esprit critique et la rigueur scientifique. Ensuite, je remercie un trio de chercheur, Hector Flores, Matthieu Puech et Yanbin Yang. Ces trois personnes m’ont beaucoup appris concernant le traitement des données et les simulations numériques. Un remerciement spécial pour Matthieu qui à passer en plus du temps à relire et corriger mes écrits scientifiques. Je remercie aussi Karen Disseau pour sa relecture attentive de ma thèse et ses corrections orthographiques et Marc Joos pour ses conseils en latex. Plus éloignés de mon travail mais proches géographiquement, il faut aussi que je remercie mes collègues actuels mais aussi passés de mon laboratoire, le GEPI. Il y a trop de monde à citer pour ne pas en oublier entre les anciens et les actuels doctorants (Myriam, Rodney, Loïc, Thierry, Anand, Xuchui, Gohuo, Cathy, Lauriane, Mélanie, Hélène, Rossella, Chloé, Céline, . ), les Post- Doc (Jianling, Susanna, Cyril, Paola, . ), les membres permanents des équipes scientifiques (Chantal, David, Marc, Piercarlo, Catherine, . ), les personnes du pôle instrumental avec qui ont été fait tant de goûter (Phillippe, Gilles, Delphine, Mathieu, Jean-Philippe, Pascal, . ), les secrétaires (Sabine, les deux Pascale, . ) qui ont toujours été présentes dans ce domaine où je suis si mauvais, l’administration, l’équipe informatique (Sylvestre, Michèle, Patrick) et aussi les stagiaires de M1 et M2 de passage au GEPI durant l’été (Celino, Cateline, Lisheng, Grégory, Raphaël, Ingrid, . ). Ces quatre années de doctorat sont aussi quatre années de monitorat. En effet, pendant trois ans j’ai eu des étudiants à l’Université Paris VII et j’ai été recruté en tant qu’ATER pour ma dernière année de thèse. Cela a été une expérience très enrichissante ; enseigner oblige à revoir les bases d’anciens cours et l’on en apprend autant si ce n’est plus que nos étudiants. Là encore beaucoup de personnes à remercier. Les premières font parties des équipes pédagogiques des cours dans lesquels j’étais impliqué à Paris VII, cours de Mécanique en L1 en particulier (Martine, Yves, Antoine, . ), cours d’hydrodynamique en L1 (Patrice, . ), TP d’optique en L3 (Gerard, . ) et TD d’informatique. Grâce à eux j’ai pu découvrir le métier d’enseignant chercheur, mais aussi grâce à mes collègues durant mon ATER à l’observatoire de Meudon (Chantal, Matthieu, Audrey, Françoise, . ). En dehors du milieu professionnel, il y a évidemment les membres de ma famille avec en tête mes parents qu’il faut remercier pour leur soutien durant ces quatre années. Enfin, la vie ne se réduisant pas seulement au travail, je remercie mes amis, les plus anciens (Christophe, Mathieu, Claire, Khanh-Dang, Nicolas, Jonathan, Chloé, Godefroy, Marc, . ) comme les nouveaux fait durant mon M2 et ma thèse (Sophie, Laurent, Jennyfer, Romain S. et H., Anne, Benjamin, Morgan, Matteo, Laure, . ). Résumé La découverte de l’expansion de l’univers par Edwin Hubble en 1929 et l’étude de modèles cosmologiques ont retiré à l’univers son image statique et infinie ; l’univers évolue depuis plus de 13 milliards d’années, depuis le Big Bang. Le modèle cosmologique standard hiérarchique ΛCDM prédit que, durant cette évolution, les halos de matière noire auraient principalement accrété de la masse par fusions successives. L’évolution des baryons, qui se trouveraient être en quantité bien plus faible, aurait suivi celle de la matière noire. Deux types de fusions auraient structuré l’évolution des galaxies : les fusions mineures et majeures. De plus, une accrétion continue de gaz froid, similaire à de nombreuses fusions mineures, aurait aussi pu jouer un rôle dans l’assemblage de la masse des galaxies. Les fusions mineures et l’accrétion de gaz entraînent une évolution douce des galaxies. A contrario, les fusions majeures modifient brutalement la morphologie aussi bien que la cinématique des galaxies en fusion et forment ainsi de nouvelles galaxies. Une dernière forme d’évolution apparaît lorsque la galaxie est isolée ou pendant une période séparant deux épisodes de fusion : l’évolution séculaire. La morphologie et la cinématique d’une galaxie peuvent alors changer via des perturbations internes ou générées par la dernière fusion. L’évolution séculaire n’ajoute pas de masse à la galaxie ; seule, elle est insuffisante pour créer une galaxie. Pour mieux contraindre l’évolution des galaxies, je me suis tout d’abord penché sur l’évolution des galaxies durant les huit derniers milliards d’années. Dans cette optique, j’ai travaillé sur des données observationnelles du programme IMAGES (Intermediate MAss Galaxies Evolution Sequence), une étude, basée sur 63 galaxies situées à des redshifts intermédiaires (z 0.6), ∼ ayant pour objectif de dresser un portrait de l’état des galaxies à redshifts intermédiaires et de comprendre les mécanismes à l’oeuvre dans leur évolution. J’ai principalement utilisé les méthodes de travail développées sur l’échantillon du projet IMAGES pour 12 nouvelles galaxies ayant un redshift moyen légèrement plus grand (z 0.7 au lieu de 0.6). Avec les données ∼ du HST provenant du relevé GOODS, j’ai classé morphologiquement les galaxies du nouvel échantillon. Puis, utilisant les données du spectrographe multi-objets GIRAFFE, j’ai déterminé la cinématique de ces galaxies. Je retrouve, pour une plus petite statistique, les résultats du projet IMAGES : la fraction importante de galaxies particulières qui représentent plus de 50 % des galaxies de masses intermédiaires à des redshifts intermédiaires, au détriment des galaxies spirales ; une corrélation entre la classe morphologique des galaxies spirales et celle cinématique des galaxies en rotation ; une tendance pour les galaxies particulières à avoir une cinématique complexe ou perturbée. Ces résultats impliquent que les galaxies ont changé de morphologie entre z = 0.7 et z = 0. Les galaxies ayant une cinématique complexe ou perturbée sur de grandes échelles (> 5 kpc) requièrent des mécanismes bouleversant l’ensemble du gaz. Le mécanisme d’évolution le plus apte à les expliquer est la fusion majeure plutôt que l’accrétion lente de gaz ou la fusion mineure de galaxies naines. Les galaxies elliptiques de l’univers proche étant déjà en place à z > 1, les galaxies particulières ont dû alors évoluer en galaxies spirales. Tester le scénario de reconstruction des galaxies spirales après une fusion majeure a été le second axe de mon travail de recherche. La fraction de gaz, plus élevée dans le passé (> 50 % à z 1 2), joue un rôle primordial dans ce processus de reconstruction.
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