Abstract Conspicuous morphological features such as rings, ringlenses, lenses, barlenses, and spiral arms are observed in many nearby disk galaxies. These features are believed to form due to the so-called secular evolution after the galaxies were formed, which means that their disks evolve in a more passive fashion and in longer timescales, compared to their formation processes. This slow evolution of disks is due to the effect of non-axisymmetric potentials, among which, a bar potential is perhaps the most effective of all. Strong rotating bars redistribute angular momentum and material through the disks of galaxies very effciently, and produce resonances. At these resonances the material is trapped and starts forming stars, creating beautiful rings. However, rings are not the only structure observed in disk galaxies. There are also spiral arms that, might or might not be created by bars. Other type of structures are lenses, which in images appear as flat light distributions with sharp edges, and ringlenses, whose appearance is intermediate between those of rings and lenses. Also, there are barlenses, which are conspicuous lens-like structures embedded in bars, and have been suggested to be the more face-on counterparts of Boxy/Peanut/X-shaped bulges. The study of the physical properties of all these structures provides a tool to investigate the mechanisms that create them and hence, to determine which are the processes that drive the slow evolution of galaxies. In this thesis I study the morphological structures using mainly data from the Spitzer Survey of Stellar Structure in Galaxies (S⁴G), by means of their sizes, orientations, shapes and colors. The S⁴G contains images of ~ 2500 nearby galaxies of all Hubble types at 3.6 and 4.5 μm, allowing a dust free view of the old stellar population which is subject of the secular evolution. Among the results presented in this thesis and the respective companion papers are the following. A catalog that contains the sizes, ellipticities and position angles of the morphological features in the S⁴G was created. This catalog also includes the measurements of the pitch angles of spiral arms. There is a corroboration of previous results showing that different types of morphological features appear in galaxies with different Hubble stages and bar families, and a confirmation of the resonant nature of rings but also of a high fraction of lenses and ringlenses. There is also an observation indicating that low mass galaxies lack nuclear structures such as nuclear rings due to the lack of inner Lindblad resonances caused by their low central mass concentrations. Observational evidence is presented indicating that a fraction of inner lenses in unbarred galaxies might be former barlenses of which the "thin bar" has probably dissolved or it is too faint to be detected. The sizes of barlenses show a tight linear correlation with those of bars, being the size of the barlens typically half the size of the bar. The study of the optical colors of barlenses reveals their similarity with bars, giving observational evidence that their stellar populations are similar, and distinguishes them from disks and nuclear regions. The orientations of barlenses with respect to that of bars and disks reveal that barlenses are vertically thick structures. All these results support the idea that barlenses are the vertically thick inner parts of bars and hence relate them observationally to Boxy/Peanut/X-shaped bulges. These results and others are published in a series of original papers in which I have collaborated and that are appended at the end of this work.

Cette thèse a pour but de faire le lien entre l’évolution des galaxies, leur morphologie et les processus physiques internes, notamment la formation stellaire comme le résultat du milieu interstellaire turbulent et multiphase, en utilisant les simulations cosmologiques zoom-in, les simulations des galaxies isolées et en interaction, et le modèle analytique de la formation stellaire. Dans le chapitre 1, j’explique la motivation pour cette thèse et je passe brièvement en revue le contexte nécessaire lié à la formation des galaxies et la modélisation en utilisant les simulations numériques. Tout d’abord, j’explore l’évolution de la morphologie des galaxies du type de la Voie Lactée dans la série des simulations cosmologiques zoom-in à travers l’analyse des barres. J’analyse l’évolution de la fraction des barres avec le redshift, sa dépendance en fonction de la masse stellaire et l’histoire d’accrétion de galaxies individuelles. Je montre en particulier, que la fraction de barres décroit avec le redshift croissant, en accord avec les observations. Ce travail montre également que les résultats obtenus suggèrent que l’époque de la formation des barres correspond à la transition entre une phase précoce “violente” de la formation de galaxies spirales à z > 1, pendant laquelle elles sont souvent perturbées par les fusions avec les galaxies de masse comparable ou par multiple fusions avec les galaxies de petite masse, mais aussi les instabilités violentes de disque, et une phase "séculaire" tardive à z < 1, quand la morphologie finale est généralement stabilisée vers une structure dominée par le disque. Cette analyse est présentée dans le chapitre 2. Étant donné que ces simulations cosmologiques forment trop d'étoiles trop tôt par rapport aux populations de galaxies observées, je me concentre dans le chapitre 3 sur la formation stellaire dans un échantillon de simulation de galaxies en isolation, à bas redshift, et à résolution du parsec et sous-parsec. J'étudie l'origine physique de leurs relations de formation stellaire avec les cassures, et montre que le seuil de densité surfacique pour une formation stellaire efficace peut être lié à la densité caractéristique d'apparition de turbulence supersonique. Ce résultat s'applique aussi bien aux galaxies qui fusionnent, dans lesquelles l'augmentation de la turbulence compressive déclenchée par les marées compressives les conduit au régime de sursaut de formation d'étoiles. Un modèle analytique idéalisé de formation stellaire liant la densité surfacique de gaz au taux de formation stellaire comme une fonction de la présence de turbulence supersonique et la structure associée du milieu interstellaire est ensuite présenté dans le chapitre 4. Ce modèle prédit une cassure à basse densité de surface qui est suivie par un régime de loi de puissance à haute densité dans différents systèmes en accord avec les relations de formation stellaire des galaxies observées et simulées. La dernière partie de cette thèse est dédiée à la technique alternative de zoom-in cosmologique (Martig et al. 2009) et son implémentation dans le code à raffinement de maillage adaptatif RAMSES. Dans le chapitre 5, je présente les caractéristiques de base de cette technique aussi bien que certains de nos tout premiers résultats dans le contexte de l'accrétion cosmologique diffuse. / This thesis aims at making the link between galaxy evolution, morphology and internal physical processes, namely star formation as the outcome of the turbulent multiphase interstellar medium, using the cosmological zoom-in simulations, simulations of isolated and merging galaxies, and the analytic model of star formation. In Chapter 1, I explain the motivation for this thesis and briefly review the necessary background related to galaxy formation and modeling with the use of numerical simulations. I first explore the evolution of the morphology of Milky-Way-mass galaxies in a suite of zoom-in cosmological simulations through the analysis of bars. I analyze the evolution of the fraction of bars with redshift, its dependence on the stellar mass and accretion history of individual galaxies. I show in particular, that the fraction of bars declines with increasing redshift, in agreement with the observations. This work also shows that the obtained results suggest that the bar formation epoch corresponds to the transition between an early "violent" phase of spiral galaxies formation at z > 1, during which they are often disturbed by major mergers or multiple minor mergers as well as violent disk instabilities, and a late "secular" phase at z < 1, when the final morphology is generally stabilized to a disk-dominated structure. This analysis is presented in Chapter 2. Because such cosmological simulations form too many stars too early compared to observed galaxy populations, I shift the focus in Chapter 3 to star formation in a sample of low-redshift galaxy simulations in isolation at parsec and sub-parsec resolution. I study the physical origin of their star formation relations and breaks and show that the surface density threshold for efficient star formation can be related to the typical density for the onset of supersonic turbulence. This result holds in merging galaxies as well, where increased compressive turbulence triggered by compressive tides during the interaction drives the merger to the regime of starbursts. An idealized analytic model for star formation relating the surface density of gas and star formation rate as a function of the presence of supersonic turbulence and the associated structure of the ISM is then presented in Chapter 4. This model predicts a break at low surface densities that is followed by a power-law regime at high densities in different systems in agreement with star formation relations of observed and simulated galaxies. The last part of this thesis is dedicated to the alternative cosmological zoom-in technique Martig et al. 2009 and its implementation in the Adaptive Mesh Refinement code RAMSES. In Chapter 5, I will present the basic features of this technique as well as some of our very first results in the context of smooth cosmological accretion.