The observational trend that disky elliptical galaxies exhibit younger luminosity- weighted ages than boxy ellipticals is investigated. The presence of a possible young stellar disk embedded in these galaxies is explored by comparing kinematics derived from the near-infrared Calcium II triplet (around 8600 Å) and Hβ (4863 Å) Balmer line, thought to be sensitive to older and younger stars respectively. Using synthetic stellar population spectra of these two wavelength regions, it is found that a young disk component produces observable differences in the kinematics derived from the two wavelength regions. Specifically, very young disks produce differences in the Gauss-Hermite coefficients, h(_3) and h(_4). Disks with an intermediate age produce offsets in the rotation velocities. Older disks produce clear two-component structure in the derived LOSVDs. Thus, diagnostic indicators are established which can be applied to observations. A comparison is presented of the major- and minor-axis kinematics derived from the Calcium II triplet and Hβ absorption features for a small sample of disky elliptical galaxies with enhanced Hβ absorption strength, indicative of a young component. For two galaxies in the sample, NGC 584 and NGC 821, Hβ gives a rotation velocity higher than that from the Calcium II triplet. These offsets are not consistent with the spectral models, since the offsets in velocity are not accompanied by the expected offsets in the other LOSVD parameters. This implies that the disks have either formed over time with a modest star- formation rate; or that the young stars in these systems are present in both the disk and spheroid components. From dynamical modelling of ground-based integral-field spectroscopy combined with HST STIS data, the disky elliptical NGC 821 is found to have a mass-to-light ratio of 4.12± 0.06 in I-band solar units, and harbours a central black hole of mass (3.41 ± 0.68) x 10(^7) M(_ʘ). This black hole mass is consistent with Gebhardt et al. (2002), who use the same STIS data with their independent modelling code. The phase-space distribution of the orbits in the model shows evidence for a two-component structure, which corresponds to a slowly rotating spheroidal component superimposed with a flattened, strongly rotating component. This second component, which has properties similar to a disk, accounts for 15% of the total system mass. Applying the two-component stellar population models, a disk of this mass would have formed 6 Gyr ago to produce the observed Hβ absorption. Such a disk is not consistent with the long-slit observations, as no offset was found between the Calcium II triplet and Hβ velocity dispersions. However, this cannot be strongly excluded due to the effects of metallicity and disk velocity dispersion on the spectral modelling.

In this work I have examined the spatially resolved properties of the local early- type galaxy population. Using Hubble Space Telescope and ground based pho- tometry I constructed Jeans Anisotropic Multi Gaussian Expansion models of the SAURON sample of early-type galaxies, from which I determined the depth of the local gravitational potential well, quantified by the local escape velocity, Vesc. I found that Vesc correlated tightly with the three Lick indices: Mgb, Fe5015 and Hβ. The Mgb-Vesc relation within individual galaxies is identical to that between different galaxies; the relation is both local and global. The Mgb-Vesc relation is: log Mgb = (0.35 ± 0.01) log Vesc − (0.41 ± 0.03). While the metallicity, [Z/H] is cor- related with Vesc it does not show the same local and global behaviour. Age (t) and alpha enhancement ([α/Fe]) are only weakly correlated with Vesc. A combination of [Z/H] and t is tightly correlated with Vesc, with scatter comparable to the Mgb-Vesc relation, and does show the local and global behaviour. This combination is given by: log Vesc = 0.85[Z/H] + 0.43 log t. Using the volume limited ATLAS3D sample of 260 local ETGs I examined in detail the behaviour of the Mgb-Vesc relation and its dependence on other galaxy properties. I found that systematic deviations from the relation correlate with the local environmental density and molecular gas mass of a galaxy, and with the local [α/Fe] measurement. I found that there is a population of galaxies that do not follow the relation, found only at Vesc < 400 kms−1. These galaxies have negative gradients, high central Hβ indices and young (t < 3 Gyrs) ages. Using stellar population models I demonstrated that these negative gradient galaxies are perturbed from the relation by recent star formation and will return to the relation as they age. I also describe the observation, reduction and analysis of a new sample of ETGs in the core of the Coma cluster, the highest density environment in the local Universe, observed with the SWIFT Integral Field Spectrograph. I determined the fraction of slow rotators in the sample, comparing it to results from the ATLAS3D survey, and found an enhanced slow rotator fraction in the Coma cluster. I also determined the Fundamental Plane of Coma early-type galaxies, given by: log Re = (1.20 ± 0.22) log σe − (0.79 ± 0.09) log⟨Ie⟩.

>Magister Scientiae - MSc

A simple morphological classification of the galaxies in the local Universe shows two main families: (1) the disc galaxies, with spiral arms and in two-thirds of these galaxies a stellar bar; and (2) the elliptical and lenticular galaxies, labelled early-type galaxies (ETGs), which are dominated by a spheroidal stellar component. ETGs are among the most massive galaxies of the local Universe and present a red color, meaning that their stars are old. These galaxies also present a large diversity of stellar dynamics: they may have a regular rotation pattern aligned with the photometry or perpendicular to it; they can present no global rotation at all; or may hold a central stellar component with a rotation axis distinct from the outer stellar body called a Kinematically Distinct Core (KDC). These features observed in the dynamics of the ETGs and their large mass are clearly signs of past interactions, especially signs of galaxy mergers. The main goal of my thesis is to analyse a large sample of high-resolution numerical simulations of binary galaxy mergers. These binary mergers are called "idealized" because they do not take into account the full cosmological context of galaxy formation: two isolated spiral galaxies are launched in an orbit resulting in a merger of the galaxies, the final remnant is an ETG. The statistical analysis of this large sample of simulations enables us to link the initial conditions of the merger to the final merger remnant. I demonstrated that the mass ratio between the spiral progenitors and the orientation of their spins of angular momentum are the main drivers for the formation of fast and slow rotating ETGs and the KDCs. The morphology of the initial spiral (Bulge/Disc ratio) seems also to play a major role for the formation of the different types of ETGs but its impact is not completelly clear, and other simulations are planned to clarify this problem. During my thesis, I also studied the importance of the resolution in the numerical simulations of galaxy mergers. I showed that the number of particles and the size of the computational grid have a predominant role in the final product of the merger. A too low resolution (i.e. too few particles and a coarse grid) can not follow the rapid evolution of the gravitational potential during the merger. In this case, the angular momentum is not as efficiently transfered to the outer parts of the galaxy: the merger remnant keeps thus a strong and regular rotation. At higher resolution, the scattering of the orbit is resolved and the merger remnant may end-up with, under some special initial conditions, a slow rotation and may form a KDC.

Une simple classification morphologique des galaxies de l'Univers local montre deux grandes familles: (1) les galaxies disques, avec des bras spiraux et dans deux-tiers des cas une barre stellaire; et (2) les galaxies elliptiques et lenticulaires, dites galaxies de type précoce ou early-type galaxies (ETGs), qui sont dominées par une composante stellaire sphéroidale. Les galaxies les plus massives de l'Univers local sont les ETGs. Ces galaxies présentent aussi une large variété de dynamique stellaire: elles peuvent avoir un champ de vitesse régulier et aligné avec la photométrie ou perpendiculaire à la photométrie; ne présenter aucune rotation globale; ou alors être composées de deux disques en contre-rotation l'un par rapport à l'autre (Kinematically Distinct Core ou KDC). Ces signatures dans la dynamique stellaire des ETGs et leur importante masse sont des signes d'interactions passées, en particulier des signes de fusions de galaxies. Le but principal de ma thèse est d'analyser un large échantillon de simulations numériques à haute résolution de fusions binaires de galaxies. Ces fusions sont dites "idéalisées" car elles ne prennent pas en compte le contexte cosmologique de formation des galaxies : deux galaxies en isolation sont lancées sur une orbite permettant la fusion de ces galaxies, le résultat final attendu de la fusion étant une ETG. L'analyse statistique de ce large échantillon de simulations nous permet de relier les conditions initiales de la fusion à la galaxie finale. J'ai démontré que le rapport de masse entre les spirales initiales et que l'orientation de leurs moments angulaires sont des points essentiels à la formation des ETGs avec peu ou beaucoup de rotation et des KDCs. La morphologie de la spirale (rapport Bulbe/Disque) est aussi un point important pour la formation des KDC mais son impact n'est pas clair et de nouvelles simulations sont nécessaires pour conclure. Durant ma thèse, j'ai aussi étudié l'importance de la résolution dans les simulations numériques de fusion de galaxies. J'ai montré que le nombre de particules et la taille des cellules utilisées ont une importance prépondérante dans les résultats finaux. Une trop faible résolution (i.e. peu de particules et une grille grossière) ne permet pas de suivre l'évolution rapide du potentiel gravitationnel lors de la fusion. Dans ce cas, certaines particules n'évacuent pas leur moment angulaire vers l'extérieur de la galaxie: la galaxie résultante de la fusion garde ainsi une plus forte rotation. A haute résolution, la dispersion de ces orbites est résolue, la galaxie résultante possède donc une faible rotation et peut former, sous certaines conditions initiales, un KDC. / A simple morphological classification of the galaxies in the local Universe shows two main families: (1) the disc galaxies, with spiral arms and in two-thirds of these galaxies a stellar bar; and (2) the elliptical and lenticular galaxies, labelled early-type galaxies (ETGs), which are dominated by a spheroidal stellar component. ETGs are among the most massive galaxies of the local Universe and present a red color, meaning that their stars are old. These galaxies also present a large diversity of stellar dynamics: they may have a regular rotation pattern aligned with the photometry or perpendicular to it; they can present no global rotation at all; or may hold a central stellar component with a rotation axis distinct from the outer stellar body called a Kinematically Distinct Core (KDC). These features observed in the dynamics of the ETGs and their large mass are clearly signs of past interactions, especially signs of galaxy mergers. The main goal of my thesis is to analyse a large sample of high-resolution numerical simulations of binary galaxy mergers. These binary mergers are called "idealized" because they do not take into account the full cosmological context of galaxy formation: two isolated spiral galaxies are launched in an orbit resulting in a merger of the galaxies, the final remnant is an ETG. The statistical analysis of this large sample of simulations enables us to link the initial conditions of the merger to the final merger remnant. I demonstrated that the mass ratio between the spiral progenitors and the orientation of their spins of angular momentum are the main drivers for the formation of fast and slow rotating ETGs and the KDCs. The morphology of the initial spiral (Bulge/Disc ratio) seems also to play a major role for the formation of the different types of ETGs but its impact is not completelly clear, and other simulations are planned to clarify this problem. During my thesis, I also studied the importance of the resolution in the numerical simulations of galaxy mergers. I showed that the number of particles and the size of the computational grid have a predominant role in the final product of the merger. A too low resolution (i.e. too few particles and a coarse grid) can not follow the rapid evolution of the gravitational potential during the merger. In this case, the angular momentum is not as efficiently transfered to the outer parts of the galaxy: the merger remnant keeps thus a strong and regular rotation. At higher resolution, the scattering of the orbit is resolved and the merger remnant may end-up with, under some special initial conditions, a slow rotation and may form a KDC.

Early-type galaxies (ETGs) are typically thought of as 'red and dead' with little to no star formation and old stellar populations. Their detailed kinematics measured locally suggest an interesting array of formation mechanisms and high-redshift observations are starting to reveal a two-phase evolutionary path for the most massive galaxies. In this thesis, I take a combined approach to studying the formation of ETGs. I look to distant quiescent galaxies in one of the densest regions of the early Universe and at the fossil record of a local galaxy to shed light on some of the unsolved mysteries of how ETGs evolved. Using the unique multiplexed instrument, the K-band Multi-Object Spectrograph (KMOS), the evolution of galaxies at both low and high redshift were studied as part of this thesis. I maximised the capabilities of this multi-integral field unit (IFU) near-infrared (NIR) instrument to study different aspects of ETG evolution. With 24 separate IFUs, many quiescent galaxies were efficiently observed in a massive high-redshift cluster as part of the KMOS Cluster Survey. Coupling KMOS spectroscopy with Hubble Space Telescope photometry, I studied the ages, kinematics, and structural properties of the galaxies. I then analysed the detailed properties of a massive local ETG with interesting kinematics, IC 1459. Coupling the NIR IFU data from KMOS with a large mosaic of optical data from the Multi-Unit Spectroscopic Explorer, I was able to study the spatially resolved kinematics, stellar populations, and initial mass function of the galaxy. The work presented in this thesis provides some interesting clues as to the formation of ETGs and possible diversity of their evolutionary paths.

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

>Magister Scientiae - MSc / There have been a number of attempts to measure the expansion rate of the Universe using age-dating of Luminous Red Galaxies (LRGs).Assuming stars in LRGs form at the same time, age-dating of two populations of LRGs at different redshifts can provide an estimate of the time difference associated with the corresponding redshift interval (dt/dz). This gives a direct estimate of the Hubble parameter at the average redshift of the two populations. In this thesis, we explore the validity of the assumptions in this method using LRGs identified in the Millenium Simulation.We study the properties of LRGs simulated using two semi-analytical models for galaxy evolution and discuss LRG selection criteria. We use stellar population modelling and spectral synthesis to estimate the errors on ages that can be expected and discuss optimization of an age-dating experiment.We find that H(z) using simulated galaxies from MS can be recovered with high accuracy. Using Single Stellar Populations (SSPs) to age -date LRGs is not sufficient for this experiment but if the star formation histories of galaxies are used, accurate ages are obtainable. We discuss an observing program to carry out this experiment using SALT (Southern African Large Telescope).

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.