L'étude de l'évolution de galaxies, et tout particulièrement du phénomène d'évaporation, a été pour la première fois menée à l'aide de modèles physiques, par Chandrasekhar notamment, dans les années 40. Depuis, de nouveaux modèles plus sophistiqués ont été introduits par les physiciens. Ces modèles d'évolution des galaxies sont des modèles cinétiques; bien connus et bien étudiés par les mathématiciens. Cependant, l'aspect évaporation (le fait que des étoiles sortent du système étudié) n'avait pas encore été étudié mathématiquement, à ma connaissance. La galaxie est vue comme un gaz constitué d'étoiles et le modèle consiste en une équation de Vlasov-Poisson, l'interaction étant la gravitation universelle, couplée avec au second membre un terme de collision de type Landau. On rajoute à ce modèle une condition d'évaporation qui consiste à dire que les étoiles dont l'énergie cinétique est suffisamment élevée pour quitter le système sont exclues. Ce modèle étant trop compliqué à étudier tel quel, je propose dans cette thèse plusieurs modèles simplifiés qui sont des premières étapes nécessaires à l'étude du modèle général et qui permettent de mieux comprendre les difficultés à surmonter. Dans une première partie, je m'intéresse au cas homogène en espace, pour lequel le terme de Vlasov-Poisson est remplacé par une simple dérivée en temps. Je fais une étude précise du cas à symétrie radiale en vitesse avec un potentiel Maxwellien, le terme de Landau étant alors remplacé par un terme de type Fokker-Planck, et je montre dans ce cas l'existence et l'unicité d'une solution régulière et l'existence d'un profil asymptotique des solutions. Dans le cas homogène général, je montre l'existence et l'unicité d'une solution régulière tout pendant que la masse ne s'est pas totalement évaporée. J'illustre ces résultats théoriques par des simulations numériques réalisés à l'aide de schéma numériques conservateurs. Dans une seconde partie, je m'intéresse au cas non homogène en espace en dérivant un modèle hydrodynamique pour un modèle de type Vlasov-BGK (plus simple que le modèle Vlasov-Poisson-Landau) avec évaporation. / The study of the evolution of the galaxies, and more specially of the evaporation phenomenon, was for the first time carried out, by Chandrasekhar in particular, in the 40s. Since then, more sophisticated models have been introduced by physicists. These models are kinetics models; well-known and well-studied by mathematicians. However, the evaporation (the fact that stars leave the galaxy) has never been studied before, to my knowledge. The galaxy is seen as a gaz of stars and the model is formed by a Vlasov-Poisson equation, with the gravitational interaction, coupled with Kernel of collision of Landau. A condition of evaporation is added to this model, saying the stars with a large enough kinetic energy are excluded. As this model is too complicated to be studied, I propose in this thesis several simpler models which constitute first steps toward the study of the general model and which inform us about the difficulties implied. In the first part, I am interested in the space-homogeneous model, for which the Vlasov-Poisson term is replaced by a simple time derivative. I make a precise study of the spherically symmetric case with a Maxwellian potential for which the the Landau term is replaced by a Fokker-Planck typed term, and I show the existence of a unique regular solution and the fact that this solution admits an asymptotical profile. In the general homogeneous case, I show the existence of a unique regular solution as long as the mass has not totally disappeared. Theses theoretical results are illustrated with numerical simulations obtained with conservative schemes. In the second part, I am interested in the inhomogeneous case and I derive an hydro-dynamical model for a Vlasov-BGK model (a simpler model than Vlasov-Poisson-Landau) with evaporation.

Galaxies are the major building blocks of the universe, but we are still learning about fundamental aspects of their formation. In particular, we would like to understand how galaxies acquire their stars, and where and when these stars were born. In this thesis, we investigate these questions by the study of the dynamical and chemical abundances of galaxies in the local universe. Extending previous works in the field, we have developed a Bayesian framework to obtain luminosity-weighted ages, metallicities and alpha-element abundances. In our initial study, we have surveyed six galaxy groups to understand how this particular environment may be related to morphological transformations. We have obtained a sample of 59 group members with a wide range of dynamical masses, which have been used to demonstrate that the mass-metallicity relation extends to low-mass galaxies. We then proceeded to the study of NGC 3311, a cD galaxy at the center of the Hydra I cluster. We have confirmed previous observations of the velocity dispersion profile of the system, which indicates the presence of a large photometric substructure which illustrates the ongoing accretion of the diffuse stellar halo. We performed a study of the stellar populations of the system, which indicated that stars in the diffuse stellar halo have been accreted from past merger events of large elliptical galaxies, whereas the central region of the galaxy is most probably the remnant of a rapid dissipative collapse. Moreover, the metallicity of the stars in the photometric substructure suggest an ongoing disruption of dwarf galaxies possibly related to the presence of an infalling group. These results are consistent with the two-phase model for the mass assembly of galaxies, in which massive ellipticals are formed by dissipative processes at high-redshifts, but continue to build-up their halos by the continuous accretion of satellite systems. / Galáxias são os principais blocos de construção do universo, mas ainda estamos aprendendo sobre aspectos fundamentais da sua formação. Em particular, gostaríamos de entender como as galáxias adquirem suas estrelas, e onde e quando essas estrelas nasceram. Nesta tese, investigamos estas questões pelo estudo da dinâmica e das abundâncias químicas de galáxias no universo local. Estendendo trabalhos anteriores na área, desenvolvemos um método Bayesiano para a obtenção de idades, metalicidades e abundância de elementos alfa ponderados pela luminosidade. Em nosso estudo inicial, pesquisamos seis grupos de galáxias para compreender como esse ambiente em particular pode estar relacionado às transformações morfológicas. Obtivemos uma amostra de 59 membros de grupos com uma vasta gama de massas dinâmicas, que foram utilizados para demonstrar que a relação massa-metalicidade se estende para galáxias de baixa massa. Então, procedemos ao estudo de NGC 3311, uma galáxia cD no centro do aglomerado Hydra I. Confirmamos as observações anteriores do perfil de dispersão da velocidades do sistema, que indicam a presença de uma grande subestrutura fotométrica que ilustra a acreção atual de estrelas no halo estelar difuso. Foi realizado um estudo das populações estelares do sistema, que indica que as estrelas no halo estelar difuso foram obtidas em eventos passados de fusão de grandes galáxias elípticas, enquanto que a região central da galáxia é provavelmente o remanescente de uma rápido colapso dissipativo. Além disso, a metalicidade das estrelas na subestrutura fotométrica sugere a ruptura atual de galáxias anãs relacionadas com a presença de um grupo se movimentando em direção ao centro do aglomerado. Estes resultados são consistentes com o modelo de duas fases para a acumulação da massa de galáxias, no qual galáxias elípticas gigantes são formadas por processos dissipativos em altos redshifts, mas continuam a acrescentar estrelas em seus halos pelo deposição de sistemas satélite.

Cosmological N-body simulations indicate that the dark matter haloes of galaxies should be generally triaxial. Yet, the presence of a baryonic disc is believed to modify the shape of the haloes. The goal of this thesis is to study how bar formation is affected by halo triaxiality and how, in turn, the presence of the bar influences the shape of the halo. We performed a series of collisionless and hydrodynamical numerical simulations, using elliptical discs as initial conditions. Triaxial halos tend to become more spherical and we show that part of the circularisation of the halo is due to disc growth, but part must be attributed to the formation of a bar. We find that the presence of gas in the disc is a more efficient factor than halo triaxiality in inhibiting the formation of a strong bar. / As simulações cosmológicas de N-corpos indicam que os halos de matéria escura das galáxias devem ser em geral triaxiais. Contudo, acredita-se que a presença de um disco bariônico seja capaz de alterar a forma do halo. O objetivo desta tese é o de estudar como a formação de barras é afetada pela triaxialidade do halo e como, por sua vez, a presença da barra influencia a forma do halo. Nós realizamos uma série de simulações numéricas acolisionais e hidrodinâmicas, utilizando discos elípticos como condições iniciais. Os halos triaxiais tendem a se tornar mais esféricos e nós mostramos que parte da circularização do halo é devida ao crescimento do disco, mas parte precisa ser atribuída à formação da barra. Notamos que a presença de gás no disco é um fator mais eficiente do que a triaxialidade do halo em inibir a formação de uma barra forte.

Cette these a pour objet d'une part l'analyse du releve profond FIRBACK effectue par l'INFRARED SPACE OBSERVATORY dans l'infrarouge lointain (λ=170 µm), qui a pour but d'etudier les galaxies contribuant au fond extragalactique infrarouge, et d'autre part la modelisation de l'evolution des galaxies dans le domaine spectral s'etendant de l'infrarouge moyen au submillimetrique. <br /><br />Le releve FIRBACK est constitue de 3 champs (deux boreaux et un austral) a haute latitude Galactique et de faible emission d'avant-plan, couvrant une surface totale de 3. 89 degre carres.<br /><br />J'expose tout d'abord les techniques de reduction, de traitement et d'etalonnage des donnees cosmologiques ISOPHOT. En particulier, je montre qu'en ayant determine le lobe de l'instrument, l'emission etendue est en accord entre PHOT et DIRBE. Les cartes finales sont construites, et le releve est limite par la confusion σc=45 mJy. <br /><br />Je presente ensuite les techniques d'extraction des sources et de simulation pour la photometrie, qui permettent de construire le catalogue final de 106 sources, de flux compris entre 180 mJy (4σc ) et 2.4 Jy. Le catalogue complementaire regroupe 90 sources de flux compris entre 135 et 200 mJy. Les comptages de galaxies presentent un fort exces par rapport aux modeles sans et avec evolution, et aux observations locales : ils ne sont compatibles qu'avec des scerarii de forte evolution. Les sources representent 4% du fond extragalactique a 170 µm. Les quelques identifications a d'autres longueurs d'onde (en particulier dans le domaine visible et submillimetrique) suggerent que les sources FIRBACK sont des galaxies tres lumineuses dont la majorite est locale, mais dont une fraction non negligeable se situe a des redshifts superieurs a 1.<br /> <br />Dans le but de comprendre la nature des sources FIRBACK et d'apporter <br />des contraintes sur l'evolution des galaxies infrarouges, j'ai developpe un modele phenomenologique d'evolution. En utilisant la fonction de luminosite locale observee et une famille de spectres de galaxies starburst, il est possible de contraindre l'evolution de la fonction de luminosite en ajustant toutes les donnees existantes : comptages profonds a 15, 170 et 850 µm et spectre du fond extragalactique. Je montre ainsi que l' evolution des galaxies dans le domaine couvrant l'infrarouge moyen au submillimetrique est dominee par une population de galaxies infrarouges ultra-lumineuses, dont le pic se situe a L=2.0*10^11 Luminosites solaires. Les distributions en redshift sont en accord avec les observations. Le modele permet de faire des predictions pour les futures observations spatiales de SIRTF (Spitzer), Planck et FIRST (Herschel).

L'objectif de mon travail de thèse a consisté à tenter de comprendre quels sont les mécanismes principaux à l'origine de la formation d'étoiles dans les galaxies au cours des derniers dix milliards d'années. Alors qu'il avait été proposé dans le passé que le rôle des fusions de galaxies était dominant pour expliquer l'allumage de la formation d'étoiles dans les galaxies lointaines formant leurs étoiles à de très grands taux, des études plus récentes ont au contraire mis en évidence des lois d'échelles reliant le taux de formation d'étoiles des galaxies à leur masse stellaire ou masse de gaz. La faible dispersion de ces lois semblait être en contradiction avec l'idée d'épisodes stochastiques violents de formation stellaire liés à des interactions, mais plutôt en accord avec une nouvelle vision de l'histoire des galaxies où celles-ci sont nourries de manière continue en gaz intergalactique.Nous nous sommes particulièrement intéressés à l'une de ces lois d'échelles, la relation entre le taux de formation d'étoiles (SFR) et la masse stellaire des galaxies, appelées communément la séquence principale des galaxies à formation d'étoiles. Nous avons étudié cette séquence principale, SFR-M*, en fonction de la morphologie et d'autres paramètres physiques comme le rayon, la couleur, la clumpiness. Le but étant de comprendre l'origine de la dispersion de cette relation en lien avec les processus physiques responsables de cette séquence afin d'identifier le mode principal de formation d'étoile gouvernant cette séquence. Ce travail a nécessité une approche multi-longueurs d'ondes ainsi que l'utilisation de simulations de profils de galaxies pour distinguer les différents types morphologiques de galaxies impliqués dans la séquence principale. / The goal of my PhD study consists at attempt to understand what are the main processes at the origin of the star formation in the galaxies over the last 10 billions years. While it was proposed in the past that merging of galaxies has a dominant role to explain the triggering of the star formation in the distant galaxies having high star formation rates, in the opposite, more recent studies revealed scaling laws linking the star formation rate in the galaxies to their stellar mass or their gas mass. The small dispersion of these laws seems to be in contradiction with the idea of powerful stochastic events due to interactions, but rather in agreement with the new vision of galaxy history where the latter are continuously fed by intergalactic gas. We were especially interested in one of this scaling law, the relation between the star formation (SFR) and the stellar mass (M*) of galaxies, commonly called the main sequence of star forming galaxies. We studied this main sequence, SFR-M*, in function of the morphology and other physical parameters like the radius, the colour, the clumpiness. The goal was to understand the origin of the sequence’s dispersion related to the physical processes underlying this sequence in order to identify the main mode of star formation controlling this sequence. This work needed a multi-wavelength approach as well as the use of galaxies profile simulation to distinguish between the different galaxy morphological types implied in the main sequence.

>Magister Scientiae - MSc / I combine 610 MHz Giant Metrewave Radio Telescope (GMRT) data, 1.4 GHz Very Large Array (VLA) data and 1.4 GHz Westerbork Synthesis Radio Telescope (WSRT) observations, encompassing a ∼ 4 square degree field (sq. deg. field) centred on the verification strip of the Spitzer First Look Survey (FLS) field (RA = 17h18m00s, Dec = 59◦30′30′′), to study radio sources down to fluxes of about 0.1 mJy. The results of an analysis of a sample of 107 multi-component radio sources obtained by cross-correlating the VLA and GMRT catalogues are shown. The spectral index analysis shows that the majority of multi-component sources are steep-spectrum sources. Nevertheless the spread in the spectral distribution is wide, with a significant number of ultrasteep,flat or inverted sources. By cross-correlating 107 multi-component radio sources with the optical catalogues of Marleau et al. (2007) and Papovich et al. (2006), 23 objects were identified and spectroscopically classified as galaxies. Some of them are classified as star-forming or star-burst galaxies, perhaps indicating that AGN and starformation activity are ongoing in the same galaxy. The measured redshifts span the range 0 < z < 1.8 and peak at z ∼ 0.2. According to their radio power (P), 6 of the identified objects are in the range of FR II sources (P1.4GHz > 1024.5W/Hz) while 17 are in the range of FR I sources (P1.4GHz < 1024.5W/Hz). Most of the sources having P1.4GHz < 1024.5W/Hz are compact and few are extended and peculiar, while all sources in the range of P1.4GHz > 1024.5W/Hz are extended. Further optical followup is recommended to allow a more complete census of the sub-mJy population and more information on AGN feedback from such sources.

Cosmological N-body simulations indicate that the dark matter haloes of galaxies should be generally triaxial. Yet, the presence of a baryonic disc is believed to modify the shape of the haloes. The goal of this thesis is to study how bar formation is affected by halo triaxiality and how, in turn, the presence of the bar influences the shape of the halo. We performed a series of collisionless and hydrodynamical numerical simulations, using elliptical discs as initial conditions. Triaxial halos tend to become more spherical and we show that part of the circularisation of the halo is due to disc growth, but part must be attributed to the formation of a bar. We find that the presence of gas in the disc is a more efficient factor than halo triaxiality in inhibiting the formation of a strong bar. / As simulações cosmológicas de N-corpos indicam que os halos de matéria escura das galáxias devem ser em geral triaxiais. Contudo, acredita-se que a presença de um disco bariônico seja capaz de alterar a forma do halo. O objetivo desta tese é o de estudar como a formação de barras é afetada pela triaxialidade do halo e como, por sua vez, a presença da barra influencia a forma do halo. Nós realizamos uma série de simulações numéricas acolisionais e hidrodinâmicas, utilizando discos elípticos como condições iniciais. Os halos triaxiais tendem a se tornar mais esféricos e nós mostramos que parte da circularização do halo é devida ao crescimento do disco, mas parte precisa ser atribuída à formação da barra. Notamos que a presença de gás no disco é um fator mais eficiente do que a triaxialidade do halo em inibir a formação de uma barra forte.

Galaxies are the major building blocks of the universe, but we are still learning about fundamental aspects of their formation. In particular, we would like to understand how galaxies acquire their stars, and where and when these stars were born. In this thesis, we investigate these questions by the study of the dynamical and chemical abundances of galaxies in the local universe. Extending previous works in the field, we have developed a Bayesian framework to obtain luminosity-weighted ages, metallicities and alpha-element abundances. In our initial study, we have surveyed six galaxy groups to understand how this particular environment may be related to morphological transformations. We have obtained a sample of 59 group members with a wide range of dynamical masses, which have been used to demonstrate that the mass-metallicity relation extends to low-mass galaxies. We then proceeded to the study of NGC 3311, a cD galaxy at the center of the Hydra I cluster. We have confirmed previous observations of the velocity dispersion profile of the system, which indicates the presence of a large photometric substructure which illustrates the ongoing accretion of the diffuse stellar halo. We performed a study of the stellar populations of the system, which indicated that stars in the diffuse stellar halo have been accreted from past merger events of large elliptical galaxies, whereas the central region of the galaxy is most probably the remnant of a rapid dissipative collapse. Moreover, the metallicity of the stars in the photometric substructure suggest an ongoing disruption of dwarf galaxies possibly related to the presence of an infalling group. These results are consistent with the two-phase model for the mass assembly of galaxies, in which massive ellipticals are formed by dissipative processes at high-redshifts, but continue to build-up their halos by the continuous accretion of satellite systems. / Galáxias são os principais blocos de construção do universo, mas ainda estamos aprendendo sobre aspectos fundamentais da sua formação. Em particular, gostaríamos de entender como as galáxias adquirem suas estrelas, e onde e quando essas estrelas nasceram. Nesta tese, investigamos estas questões pelo estudo da dinâmica e das abundâncias químicas de galáxias no universo local. Estendendo trabalhos anteriores na área, desenvolvemos um método Bayesiano para a obtenção de idades, metalicidades e abundância de elementos alfa ponderados pela luminosidade. Em nosso estudo inicial, pesquisamos seis grupos de galáxias para compreender como esse ambiente em particular pode estar relacionado às transformações morfológicas. Obtivemos uma amostra de 59 membros de grupos com uma vasta gama de massas dinâmicas, que foram utilizados para demonstrar que a relação massa-metalicidade se estende para galáxias de baixa massa. Então, procedemos ao estudo de NGC 3311, uma galáxia cD no centro do aglomerado Hydra I. Confirmamos as observações anteriores do perfil de dispersão da velocidades do sistema, que indicam a presença de uma grande subestrutura fotométrica que ilustra a acreção atual de estrelas no halo estelar difuso. Foi realizado um estudo das populações estelares do sistema, que indica que as estrelas no halo estelar difuso foram obtidas em eventos passados de fusão de grandes galáxias elípticas, enquanto que a região central da galáxia é provavelmente o remanescente de uma rápido colapso dissipativo. Além disso, a metalicidade das estrelas na subestrutura fotométrica sugere a ruptura atual de galáxias anãs relacionadas com a presença de um grupo se movimentando em direção ao centro do aglomerado. Estes resultados são consistentes com o modelo de duas fases para a acumulação da massa de galáxias, no qual galáxias elípticas gigantes são formadas por processos dissipativos em altos redshifts, mas continuam a acrescentar estrelas em seus halos pelo deposição de sistemas satélite.

Theories of how galaxies form and evolve depend greatly on constraints provided by observations. However, when those observations come from different datasets, systematic offsets may occur. This causes difficulties measuring variations in parameters between filters. In this thesis I present the variation in total luminosity density with wavelength in the nearby Universe (z<0.1), produced from a consistent reanalysis of NIR and optical observations, taken from the MGC, UKIDSS and SDSS surveys. I derive luminosity distributions, best-fitting Schechter function parameterisations and total luminosity densities in ugrizYJHK, and compare the variation in luminosity density with cosmic star formation history (CSFH) and initial mass function (IMF) models. I examine the r band luminosity distribution produced using different aperture definitions, the joint luminosity- surface brightness (bivariate brightness) distribution in ugrizYJHK, comparing them to previously derived distributions, and how the total luminosity density varies with wavelength when surface brightness incompleteness is accounted for. I find the following results. (1) The total luminosity density calculated using a non-Sersic (e.g. Kron or Petrosian) aperture is underestimated by at least 15%, (2) Changing the detection threshold has a minor effect on the best-fitting Schecter parameters, but the choice of Kron or Petrosian apertures causes an offset between datasets, regardless of the filter used to define the source list, (3) The decision to use circular or elliptical apertures causes an offset in M* of 0.20 mag, and best-fitting Schechter parameters from total magnitude photometric systems have a flatter faint-end slope than Kron or Petrosian photometry, (4) There is no surface brightness distribution evolution with luminosity for luminous galaxies, but at fainter magnitudes the distribution broadens and the peak surface brightness dims. A Choloniewski function that is modified to account for this surface brightness evolution fits the bivariate-brightness distribution better than an unmodified Choloniewski function, (5) The energy density per unit interval, vf(v) derived using MGC and GAMA samples agrees within 90% confidence intervals, but does not agree with predictions using standard CSFH and IMF models. Possible improvements to the data and alterations to the theory are suggested.

Cette thèse est consacrée à l'étude de la formation et de l'évolution des galaxies. La mise à disposition de la communauté par l'ESO du spectrographe à multi-intégrales de champ FLAMES/GIRAFFE représente une opportunité unique d'étudier la dynamique des galaxies à z<1, et de pouvoir ainsi relier les populations distantes aux populations locales. Nous présentons dans un premier temps les résultats obtenus grâce à cet instrument dans le cadre du temps garanti de l'Observatoire de Paris (GEPI). Ces résultats montrent que la fraction de galaxies n'ayant pas encore atteint leur équilibre dynamique à z~0.6 est importante. Cette fraction est encore plus importante parmi les galaxies compactes lumineuses (LCGs), ce qui supporte l'hypothèse selon laquelle ces galaxies sont des systèmes en cours de fusion. Jusqu'à présent, l'utilisation de la spectroscopie à fente ne permettait pas de distinguer efficacement les systèmes relaxés des systèmes non relaxés, ce qui explique les désaccords concernant l'évolution de la relation de Tully-Fisher. Les résultats présentés dans cette thèse montrent en effet une non évolution de cette relation dans le plan vitesse-masse stellaire. Enfin, GIRAFFE avec son mode IFU montre la pertinence de la cartographie physico-chimique du milieu interstellaire dans la compréhension des mécanismes liés aux processus de formation stellaire dans les galaxies distantes. L'extension des méthodes de spectroscopie intégrale de champ à z>1 requiert d'explorer leur couplage avec des techniques d'optique adaptative. Le projet FALCON (à la fois dédié aux VLTs et aux ELTs) propose une nouvelle voie prometteuse dans cette direction en introduisant le concept d'optique adaptative multi-objets (MOAO). Dans ce concept, seules les zones d'intérêt scientifique sont corrigées et analysées, ce qui nécessite le développement de systèmes miniaturisés de correction de front d'onde ainsi que d'une stratégie de commande originale en boucle ouverte.