Dark matter is now accepted as an integral part of our universe, and galaxy dynamics have long provided the most convincing observational evidence for dark matter. Spiral galaxies have traditionally been used for these studies because of their more simple kinematics, however elliptical galaxies need to be understood as well. In this dissertation I present deep long-slit spectroscopy from the University of Texas’ Hobby-Eberly Telescope for a sample of elliptical galaxies. For a subsample of galaxies I fit axisymmetric orbit-superposition models with a range of dark halo density profiles. I find that all three galaxies modeled require a significant dark halo to explain their motions. However, the shape of the dark halo is not the expected NFW profile, but rather a profile with a flat central slope. I also discuss the galaxy masses, anisotropies, and stellar mass-to-light ratios. / text

Since the 30's and Edwin Hubble's famous classification, galaxies are usually separated in twogroups : the late-type galaxies (LTGs) and the early-type galaxies (ETGs). The LTGs family ismainly made of spiral galaxies (S) while the ETGs family is composed of elliptical (E) and lenticular(S0) galaxies. A morphological study of all these galaxies revealed that around 60% of LTGs and45% of S0 present a bar. It has also been shown that, in the local Universe, galaxies fall into twobig groups : the blue cloud mostly populated by LTGs and the red sequence mainly made of ETGs.Several mechanisms are responsible for this distribution and the secular evolution is obviously animportant one to examine, sepcially in the context of bars, as an important number of studiesshowed the importance of bars in the dynamics and evolution of a galaxy.The goal of my thesis is to study the importance of the formation and ensued bar-drivenevolution influence on ETGs evolution. In that context, I have performed N-body simulations ofbarred (and unbarred) galaxies in order to investigate the following issues.First of all, I focused on the influence of a bar in a galaxy when modelling it with a dynamicalmodel assuming an axisymmetric mass distribution. As these kinds of models allow to determine themass-to-light ratio M/L, thus the dynamical mass of an observed galaxy, but also its inclinationand its anisotropy, it is important to evalute the consequence of the presence of a bar on theseparameters. I have shown that, depending on the galaxy inclination and the bar position angle,M/L is most of the time biased and overestimated, and this can be up to 25%. The size andstrength of the bar also seem to be important factors but a deeper study has to be done to quantifythis preliminary result.In a second step, I have studied the role of bars on the mass and metallicity redistributionsin a lenticular galaxy. I confirmed that the presence of a bar, due to its influence on its hostsystem dynamics, flattens pre-existing metallicity gradients. Moreover, I showed that the degree offlattening and the position of affected regions are directly correlated with the bar structure and thelocation of the dynamical resonances. Nonetheless, this dynamical effect cannot explain the varietyof observed ages and metallicity gradients. The consequences of a barred gravitational potentialon the gas dynamics and the stellar formation should therefore be investigated. This is the topicof the last set of numerical simulations produced which will allow to better understand the globalinfluence a bar has on the secular evolution of ETGs.

Remarkably, the central regions of galaxies are very important in shaping and influencing galaxies as a whole. As such, galaxy cores can be used for classification, to determine which processes may be important in galaxy formation and evolution. Past studies, for example, have found a dichotomy in the inner slopes of early-type galaxy surface brightness profiles. Using deprojections of the galaxies from the ACS Virgo and Fornax Cluster Surveys (ACSVCS/FCS), we show that, in fact, this dichotomy does not exist. Instead, we demonstrate that the brightest early-type galaxies tend to have central light deficits, a trend which gradually transitions to central light excesses – also known as compact stellar nuclei – as we go to fainter galaxies. This effect is quantified, and can be used to determine what evolutionary factors are important as we move along the galaxy luminosity function. The number of stellar nuclei that we observe is, in fact, an unexpected result emerging from the ACSVCS/FCS. Being three times more common than previously thought, they are present in the vast majority of intermediate and low-luminosity galaxies. Conversely, it has been known for over a decade that there is likely a supermassive black hole weighing millions to billions of solar masses at the center of virtually every galaxy of sufficient size. These black holes are known to follow scaling relations with their host galaxies. Using the ACSVCS, along with new kinematical data from long-slit spectroscopy, we measure the dynamical masses of 83 galaxies, and show that supermassive black holes and nuclei appear to fall along the same scaling relation with host mass. Both represent approximately 0.2% of their host’s mass, implying an important link between the two types of central massive objects. Finally, we extract elliptical isophotes and fit parameterized models to the surface brightness profiles of new Hubble Space Telescope imaging of the ACSVCS galaxies, observed in infrared and ultraviolet bandpasses. Taken together, the two surveys represent an unprecedented collection of isophotal and structural parameters of early-type galaxies, and will allow us to learn a great deal about the stellar populations and formation histories of galaxy cores. / Graduate

Depuis la célèbre classification d’Edwin Hubble dans les années 30, il est coutume de définir unegalaxie comme appartenant soit au groupe des galaxies dites de type tardif (late-type galaxiesabr´eg´e LTGs) soit à celui des galaxies dites de type précoce (early-type galaxies ou ETGs). Lafamille des LTGs est principalement composée de galaxies spirales (S) quand la famille des ETGsregroupe les galaxies lenticulaires (S0) et elliptiques (E). L’étude morphologique de ces galaxies arévélé qu’environ 60% des LTGs et 45% des S0 présentent une barre. Par ailleurs, il a été montréque dans l’Univers local les galaxies pouvaient être séparées en deux grands ensembles : le nuagebleu composé majoritairement de LTGs et la séquence rouge peuplée principalement par les ETGs.Plusieurs mécanismes sont à l’origine de cette distribution et l’évolution séculaire en est évidemmentun point majeur. Un nombre important de recherches ont montré l’importance des barres sur ladynamique et l’évolution d’une galaxie. Le but de ma th`ese est d’´etudier `a quel point la formationd’une barre et l’évolution qui s’ensuit influe sur l’évolution des ETGs. Pour ce faire j’ai réalisédes simulations à N-corps de galaxies barrées (et non barr´ees) qui m’a permis d´étudier les pointssuivants.Je me suis tout d’abord penché sur l’impact de la présence d’une barre dans une galaxie sur unemodélisation de cette dernière par un modèle supposant une ditribution de masse axisymmétrique.Ce genre de modélisation permettant de déterminer le rapport masse/luminosité M/L et donc lamasse d’une galaxie observée mais ´egalement son inclinaison et son anisotropie, il est importantd’estimer l’impact de la présence d’une barre sur ces paramètres. J’ai donc montré qu’en fonctionde l’inclinaison de la galaxie et de la position de la barre par rapport à l’observateur, le rapportM/L était très souvent surestimé avec des erreurs allant jusqu’`a 25%. La taille et la force de labarre sont également apparus comme des facteurs importants mais une étude plus approfondies’imposerait afin de quantifier ce résultat.D’autre part, je me suis intéressé à l’impact d’une barre sur la distribution de masse et de métauxdans une galaxie lenticulaire. J’ai tout d’abord confirmé que la présence d’une barre, de partson influence sur la dynamique d’un système, applatissait les gradients de métallicité. De plusj’ai montré que le degrés d’aplatissement ainsi que la position des zones affectées peuvent êtredirectement mis en relation avec la structure de la barre et notament avec la localisation desrésonances dynamiques. Néanmoins l’influence purement dynamique d’une barre n’explique pasà elle seule les gradients d’âges et de m´etallicité observés. L’étude de l’influence d’un potentielgravitationnel barré sur la dynamique du gaz et donc sur la formation stellaire est donc égalementà prendre un compte. Cela fait l’objet des dernières simulations produites qui permettront de mieuxcomprendre l’influence global d’une barre sur l’évolution séculaire des galaxies de type précoce. / Since the 30’s and Edwin Hubble’s famous classification, galaxies are usually separated in twogroups : the late-type galaxies (LTGs) and the early-type galaxies (ETGs). The LTGs family ismainly made of spiral galaxies (S) while the ETGs family is composed of elliptical (E) and lenticular(S0) galaxies. A morphological study of all these galaxies revealed that around 60% of LTGs and45% of S0 present a bar. It has also been shown that, in the local Universe, galaxies fall into twobig groups : the blue cloud mostly populated by LTGs and the red sequence mainly made of ETGs.Several mechanisms are responsible for this distribution and the secular evolution is obviously animportant one to examine, sepcially in the context of bars, as an important number of studiesshowed the importance of bars in the dynamics and evolution of a galaxy.The goal of my thesis is to study the importance of the formation and ensued bar-drivenevolution influence on ETGs evolution. In that context, I have performed N-body simulations ofbarred (and unbarred) galaxies in order to investigate the following issues.First of all, I focused on the influence of a bar in a galaxy when modelling it with a dynamicalmodel assuming an axisymmetric mass distribution. As these kinds of models allow to determine themass-to-light ratio M/L, thus the dynamical mass of an observed galaxy, but also its inclinationand its anisotropy, it is important to evalute the consequence of the presence of a bar on theseparameters. I have shown that, depending on the galaxy inclination and the bar position angle,M/L is most of the time biased and overestimated, and this can be up to 25%. The size andstrength of the bar also seem to be important factors but a deeper study has to be done to quantifythis preliminary result.In a second step, I have studied the role of bars on the mass and metallicity redistributionsin a lenticular galaxy. I confirmed that the presence of a bar, due to its influence on its hostsystem dynamics, flattens pre-existing metallicity gradients. Moreover, I showed that the degree offlattening and the position of affected regions are directly correlated with the bar structure and thelocation of the dynamical resonances. Nonetheless, this dynamical effect cannot explain the varietyof observed ages and metallicity gradients. The consequences of a barred gravitational potentialon the gas dynamics and the stellar formation should therefore be investigated. This is the topicof the last set of numerical simulations produced which will allow to better understand the globalinfluence a bar has on the secular evolution of ETGs.

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