The character of the first galaxies at redshifts z [greater-than or equal to] 10 strongly depends on the star formation which takes place during their assembly. Conducting cosmological hydrodynamics simulations, we study how the radiative output and chemical enrichment from the first stars impacts the properties of the first galaxies. We find that the radiative feedback from the first stars suppresses the star formation rate at redshifts z [greater-than or equal to] 15 by a factor of only a few. In turn, this suggests that a large fraction of the first galaxies may form from gas which has already been enriched with the first heavy elements ejected by primordial supernovae. In order to characterize the properties of primordial dwarf galaxies, we carry out radiation hydrodynamics simulations which allow to determine how the luminosities in hydrogen and helium emission lines depend on the initial mass function of the stars in the galaxy. As well, we show that the chemical abundance patterns observed in metal-poor Galactic halo stars contain the signature of the first supernovae, and we use this data to indirectly probe the properties of the first stars. / text

Uma previsão fundamental do cenário L cold dark matter (LCDM) na formação de estruturas é que os halos galácticos de DM do tamanho da Via Láctea (MW) crescem pela acreção de subsistemas menores. Neste contexto, simulações deNcorpos prevêem um número de sub-halos de matéria escura, cujo tamanho e massa são comparáveis às galáxias anãs, que é muito maior do que as galáxias satélites conhecidas. Este é o que se convencionu chamar de problema das satélites faltantes (MSP). A interpretação mais popular do MSP é que os sub-halos de matéria escura menores são extremamente ineficientes na formação de estrelas, o que torna mais difícil detectá-los. Com a chegada dos grandes levantamentos fotométricos, nos últimos anos, a descoberta de uma nova população de galáxias satélites que orbitam a MW fornece evidências empíricas para acreditar que realmente existem várias galáxias pouco luminosas não detectadas ou que simplesmente habitam regiões no céu que ainda não foram observadas. Neste trabalho implementamos um algoritmo estatístico eficiente para detectar subestruturas ultra fracas da MW. O código, chamado SPARSEX, foi testado e otimizado usando um conjunto de objetos estelares previamente identificados nos dados do Sloan Digital Sky Survey (SDSS), conseguindo recuperar todos os objetos com sucesso. Além disso, a aplicação do algoritmo aos dados dos dois primeiro anos do Dark Energy Survey (DES) deu como resultado centenas de candidatos a sistemas estelares. Dezessete sistemas estelares detectados em comum com outras técnicas de busca por subestruturas, implementadas dentro do grupo de colaboração do DES, foram publicados em três artigos em 2015. Um dos candidatos publicados é o aglomerado estelar DES 1. DES1 foi detectado pelo código SPARSEX com uma alta significância estatística e aparece nas imagens do DES como uma concentração compacta de fontes pontuais azuis. O sistema estelar é consistente com uma população velha e pobre em metal. Assumindo dois diferentes perfis de densidade, os quais permitem estimar a probabilidade de que cada estrela realmente pertença ao sistema, determinamos uma distância heliocêntrica e uma magnitude absoluta total num intervalo de 77.6—87.1 kpc e 3.00 . MV . 2.21, respectivamente. O raio à meia-luz desse objeto, rh 9.88 pc, e a luminosidade são consistentes com um aglomerado estelar de baixa luminosidade do halo externo. DES1 também é x alongado (e 0.6), o que faz supor que este objeto está em estágio avançado de dissolução. Mais tarde, através de uma cuidadosa reanálise de nossos resultados, dois novos candidatos foram detectados, DES J01111341 e DES J0225+0304. Os candidatos estão localizados a uma distância heliocêntrica de 25 kpc e parecem também estar dominados por populações estelares velhas e pobres em metais. Suas distâncias ao plano orbital da galáxia anã de Sagitário, 1.73 kpc (DES J01111341) e 0.50 kpc (DES J0225+0304), indicam que eles estão possivelmente associados com a corrente da anã de Sagitário. O raio à meia-luz (rh ' 4.55 pc) e a luminosidade (MV ' +0.3) de DES J01111341 são consistentes com um aglomerado estelar ultra fraco, enquanto o raio à meia-luz (rh ' 18.55 pc) e a luminosidade (MV ' 1.1) de DES J0225+0304 colocam este objeto em uma região ambígua do plano tamanho-luminosidade entre aglomerados estelares e galáxias anãs. Determinações dos parâmetros característicos da corrente de Sagitário, tais como o espalhamento de metalicidade (2.18 . [Fe/H] . 0.95) e o gradiente de distância (23 kpc . D . 29 kpc), dentro da área amostrada do DES no hemisfério sul, também indicam uma possível associação com estes sistemas. Se esses objetos forem confirmados através de follow-up espectroscópico como sistemas ligados gravitacionalmente e compartilharem uma trajetoria Galáctica com a corrente de Sagitário, DES J01111341 e DES J0225+0304 seriam os primeiros sistemas estelares ultra fracos associados com tal corrente. Recentemente, nós reportamos a descoberta de um novo aglomerado estelar, DES 3. O novo sistema foi detectado como uma sobredensidade estelar nos dados do primeiro ano do DES e confirmado com follow-up fotométrico obtido com o Southerm Astrophysical Research (SOAR) Telecope. Nós determinamos que DES 3 está localizado a uma distância heliocêntrica de 76 kpc e é dominado por uma população velha (' 9.8Ganos) e pobre em metal ([Fe/H] ' 1.88). Embora os valores de idade e metalicidade de DES 3 são semelhantes aos aglomerados globulares, o seu raio à meia-luz (rh 6.5 pc) e a luminosidade (MV 1.9) são mais indicativos de um aglomerados estelar fraco. Com base no tamanho angular aparente, o DES 3, com um valor de rh 0.03, está entre os menores aglomerados estelares fracos conhecidos até à data. Estas novas detecções indicam que o censo de satélites da MW é ainda incompleto. A identificação e estudo de novos satélites em futuros surveys, como por exemplo o Large Synoptic Survey Telescope (LSST) será crucial para a nossa compreensão das subestruturas existentes no halo Galáctico e a evolução da Galáxia como um todo. / A fundamental prediction of the L cold dark matter (LCDM) scenario of structure formation is that galactic DM haloes of the size of the Milky Way (MW) grow by the accretion of smaller sub-systems. In this context, Nbody simulations predict a number of dark matter subhalos, with size and mass comparable to dwarf galaxies, but which is much larger than currently known satellite galaxies. This is what is conventionally called the missing satellites problem (MSP). The most popular interpretation of the MSP is that the smaller dark matter subhalos are extremely inefficient in star formation, making it more difficult to detect them. With the arrival of large photometric surveys, in recent years, the discovery of a new population of satellite galaxies orbiting the MW provides empirical evidence to believe that there are actually several low luminosity galaxies that were not yet detected or that simply inhabit regions in the sky that have not yet been observed. In this work we present an efficient statistical algorithm to detect ultra-faint MW substructures. The code, called SPARSEX, was tested and optimized using a set of stellar objects previously identified in the Sloan Digital Sky Survey (SDSS) data. It has detected successfully all known objects. In addition, the algorithm was applied on the first two years of Dark Energy Survey (DES) data, resulting in hundreds of stellar system candidates. Seventeen stellar systems detected in common with other substructure search techniques implemented within the DES collaboration were published in three papers in 2015. In particular, one published candidate is a star cluster, DES 1. DES 1 was detected by the SPARSEX code with high statistical significance and appears in DES images as a compact concentration of blue point sources. The stellar system is consistent with being dominated by an old and metal-poor population. Assuming two different density profiles, based on which we may evaluate a membership probability for each star, we determined a heliocentric distance and total absolute magnitude in the ranges of 77.6—87.1 kpc and 3.00 . MV . 2.21, respectively. The half-light radius of this object, rh 9.88 pc, and luminosity are consistent with a low-mass halo star cluster. DES1 is also elongated (e 0.6), which suggests that this object is in advanced stage of dissolution. Later, through a careful reanalysis of our results, two new candidates were detected, DES J01111341 e DES J0225+0304. The candidates are located at a heliocentric xii distance of 25 kpc and appear to have old and metal-poor populations as well. Their distances to the Sagittarius dwarf orbital plane, 1.73 kpc (DES J01111341) and 0.50 kpc (DES J0225+0304), indicate that they are possibly associated with the Sagittarius dwarf stream. The half-light radius (rh ' 4.55 pc) and luminosity (MV ' +0.3) of DES J01111341 are consistent with it being an ultra-faint star cluster, while the half-light radius (rh ' 18.55 pc) and luminosity (MV ' 1.1) of DES J0225+0304 place it in an ambiguous region of size-luminosity space between star clusters and dwarf galaxies. Determinations of the characteristic parameters of the Sagittarius stream, such as its metallicity spread (2.18 . [Fe/H] . 0.95) and distance gradient (23 kpc . D . 29 kpc), within the DES footprint in the Southern hemisphere, also indicate a possible association with these systems. If theses objects are confirmed through spectroscopic follow-up to be gravitationally bound systems and to share a Galactic trajectory with the Sagittarius stream, DES J01111341 and DES J0225+0304 would be the first ultra-faint stellar systems associated with the Sagittarius stream. Recently, we reported the discovery of a new star cluster, DES 3. The new system was detected as a stellar overdensity in first-year DES data, and confirmed with deeper photometry from the Southern Astrophysical Research (SOAR) telescope. We determine that DES 3 is located at a heliocentric distance of 76 kpc and it is dominated by an old (' 9.8 Gyr) and metal-poor ([Fe/H] ' 1.88) population. While the age and metallicity values of DES 3 are similar to globular clusters, its half-light radius (rh 6.5 pc) and luminosity (MV 1.9) are more indicative of faint star clusters. Based on the apparent angular size, DES 3, with a value of rh 0.03, is among the smallest faint star clusters known to date. These new detections indicate that the MW satellites census is still incomplete. The identification and study of new satellites in future surveys, such as the Large Synoptic Survey Telescope (LSST), will be crucial to our understanding of substructures in the Galactic halo and the evolution of the Galaxy as a whole.

Uma previsão fundamental do cenário L cold dark matter (LCDM) na formação de estruturas é que os halos galácticos de DM do tamanho da Via Láctea (MW) crescem pela acreção de subsistemas menores. Neste contexto, simulações deNcorpos prevêem um número de sub-halos de matéria escura, cujo tamanho e massa são comparáveis às galáxias anãs, que é muito maior do que as galáxias satélites conhecidas. Este é o que se convencionu chamar de problema das satélites faltantes (MSP). A interpretação mais popular do MSP é que os sub-halos de matéria escura menores são extremamente ineficientes na formação de estrelas, o que torna mais difícil detectá-los. Com a chegada dos grandes levantamentos fotométricos, nos últimos anos, a descoberta de uma nova população de galáxias satélites que orbitam a MW fornece evidências empíricas para acreditar que realmente existem várias galáxias pouco luminosas não detectadas ou que simplesmente habitam regiões no céu que ainda não foram observadas. Neste trabalho implementamos um algoritmo estatístico eficiente para detectar subestruturas ultra fracas da MW. O código, chamado SPARSEX, foi testado e otimizado usando um conjunto de objetos estelares previamente identificados nos dados do Sloan Digital Sky Survey (SDSS), conseguindo recuperar todos os objetos com sucesso. Além disso, a aplicação do algoritmo aos dados dos dois primeiro anos do Dark Energy Survey (DES) deu como resultado centenas de candidatos a sistemas estelares. Dezessete sistemas estelares detectados em comum com outras técnicas de busca por subestruturas, implementadas dentro do grupo de colaboração do DES, foram publicados em três artigos em 2015. Um dos candidatos publicados é o aglomerado estelar DES 1. DES1 foi detectado pelo código SPARSEX com uma alta significância estatística e aparece nas imagens do DES como uma concentração compacta de fontes pontuais azuis. O sistema estelar é consistente com uma população velha e pobre em metal. Assumindo dois diferentes perfis de densidade, os quais permitem estimar a probabilidade de que cada estrela realmente pertença ao sistema, determinamos uma distância heliocêntrica e uma magnitude absoluta total num intervalo de 77.6—87.1 kpc e 3.00 . MV . 2.21, respectivamente. O raio à meia-luz desse objeto, rh 9.88 pc, e a luminosidade são consistentes com um aglomerado estelar de baixa luminosidade do halo externo. DES1 também é x alongado (e 0.6), o que faz supor que este objeto está em estágio avançado de dissolução. Mais tarde, através de uma cuidadosa reanálise de nossos resultados, dois novos candidatos foram detectados, DES J01111341 e DES J0225+0304. Os candidatos estão localizados a uma distância heliocêntrica de 25 kpc e parecem também estar dominados por populações estelares velhas e pobres em metais. Suas distâncias ao plano orbital da galáxia anã de Sagitário, 1.73 kpc (DES J01111341) e 0.50 kpc (DES J0225+0304), indicam que eles estão possivelmente associados com a corrente da anã de Sagitário. O raio à meia-luz (rh ' 4.55 pc) e a luminosidade (MV ' +0.3) de DES J01111341 são consistentes com um aglomerado estelar ultra fraco, enquanto o raio à meia-luz (rh ' 18.55 pc) e a luminosidade (MV ' 1.1) de DES J0225+0304 colocam este objeto em uma região ambígua do plano tamanho-luminosidade entre aglomerados estelares e galáxias anãs. Determinações dos parâmetros característicos da corrente de Sagitário, tais como o espalhamento de metalicidade (2.18 . [Fe/H] . 0.95) e o gradiente de distância (23 kpc . D . 29 kpc), dentro da área amostrada do DES no hemisfério sul, também indicam uma possível associação com estes sistemas. Se esses objetos forem confirmados através de follow-up espectroscópico como sistemas ligados gravitacionalmente e compartilharem uma trajetoria Galáctica com a corrente de Sagitário, DES J01111341 e DES J0225+0304 seriam os primeiros sistemas estelares ultra fracos associados com tal corrente. Recentemente, nós reportamos a descoberta de um novo aglomerado estelar, DES 3. O novo sistema foi detectado como uma sobredensidade estelar nos dados do primeiro ano do DES e confirmado com follow-up fotométrico obtido com o Southerm Astrophysical Research (SOAR) Telecope. Nós determinamos que DES 3 está localizado a uma distância heliocêntrica de 76 kpc e é dominado por uma população velha (' 9.8Ganos) e pobre em metal ([Fe/H] ' 1.88). Embora os valores de idade e metalicidade de DES 3 são semelhantes aos aglomerados globulares, o seu raio à meia-luz (rh 6.5 pc) e a luminosidade (MV 1.9) são mais indicativos de um aglomerados estelar fraco. Com base no tamanho angular aparente, o DES 3, com um valor de rh 0.03, está entre os menores aglomerados estelares fracos conhecidos até à data. Estas novas detecções indicam que o censo de satélites da MW é ainda incompleto. A identificação e estudo de novos satélites em futuros surveys, como por exemplo o Large Synoptic Survey Telescope (LSST) será crucial para a nossa compreensão das subestruturas existentes no halo Galáctico e a evolução da Galáxia como um todo. / A fundamental prediction of the L cold dark matter (LCDM) scenario of structure formation is that galactic DM haloes of the size of the Milky Way (MW) grow by the accretion of smaller sub-systems. In this context, Nbody simulations predict a number of dark matter subhalos, with size and mass comparable to dwarf galaxies, but which is much larger than currently known satellite galaxies. This is what is conventionally called the missing satellites problem (MSP). The most popular interpretation of the MSP is that the smaller dark matter subhalos are extremely inefficient in star formation, making it more difficult to detect them. With the arrival of large photometric surveys, in recent years, the discovery of a new population of satellite galaxies orbiting the MW provides empirical evidence to believe that there are actually several low luminosity galaxies that were not yet detected or that simply inhabit regions in the sky that have not yet been observed. In this work we present an efficient statistical algorithm to detect ultra-faint MW substructures. The code, called SPARSEX, was tested and optimized using a set of stellar objects previously identified in the Sloan Digital Sky Survey (SDSS) data. It has detected successfully all known objects. In addition, the algorithm was applied on the first two years of Dark Energy Survey (DES) data, resulting in hundreds of stellar system candidates. Seventeen stellar systems detected in common with other substructure search techniques implemented within the DES collaboration were published in three papers in 2015. In particular, one published candidate is a star cluster, DES 1. DES 1 was detected by the SPARSEX code with high statistical significance and appears in DES images as a compact concentration of blue point sources. The stellar system is consistent with being dominated by an old and metal-poor population. Assuming two different density profiles, based on which we may evaluate a membership probability for each star, we determined a heliocentric distance and total absolute magnitude in the ranges of 77.6—87.1 kpc and 3.00 . MV . 2.21, respectively. The half-light radius of this object, rh 9.88 pc, and luminosity are consistent with a low-mass halo star cluster. DES1 is also elongated (e 0.6), which suggests that this object is in advanced stage of dissolution. Later, through a careful reanalysis of our results, two new candidates were detected, DES J01111341 e DES J0225+0304. The candidates are located at a heliocentric xii distance of 25 kpc and appear to have old and metal-poor populations as well. Their distances to the Sagittarius dwarf orbital plane, 1.73 kpc (DES J01111341) and 0.50 kpc (DES J0225+0304), indicate that they are possibly associated with the Sagittarius dwarf stream. The half-light radius (rh ' 4.55 pc) and luminosity (MV ' +0.3) of DES J01111341 are consistent with it being an ultra-faint star cluster, while the half-light radius (rh ' 18.55 pc) and luminosity (MV ' 1.1) of DES J0225+0304 place it in an ambiguous region of size-luminosity space between star clusters and dwarf galaxies. Determinations of the characteristic parameters of the Sagittarius stream, such as its metallicity spread (2.18 . [Fe/H] . 0.95) and distance gradient (23 kpc . D . 29 kpc), within the DES footprint in the Southern hemisphere, also indicate a possible association with these systems. If theses objects are confirmed through spectroscopic follow-up to be gravitationally bound systems and to share a Galactic trajectory with the Sagittarius stream, DES J01111341 and DES J0225+0304 would be the first ultra-faint stellar systems associated with the Sagittarius stream. Recently, we reported the discovery of a new star cluster, DES 3. The new system was detected as a stellar overdensity in first-year DES data, and confirmed with deeper photometry from the Southern Astrophysical Research (SOAR) telescope. We determine that DES 3 is located at a heliocentric distance of 76 kpc and it is dominated by an old (' 9.8 Gyr) and metal-poor ([Fe/H] ' 1.88) population. While the age and metallicity values of DES 3 are similar to globular clusters, its half-light radius (rh 6.5 pc) and luminosity (MV 1.9) are more indicative of faint star clusters. Based on the apparent angular size, DES 3, with a value of rh 0.03, is among the smallest faint star clusters known to date. These new detections indicate that the MW satellites census is still incomplete. The identification and study of new satellites in future surveys, such as the Large Synoptic Survey Telescope (LSST), will be crucial to our understanding of substructures in the Galactic halo and the evolution of the Galaxy as a whole.

A l’échelle galactique, le paradigme lambda-CDM n’est pas prédictif. Afin d’approfondir nos connaissances dans cette gamme de taille, les satellites du Groupe Local (GL) sont les systèmes galactiques les plus simples et les plus proches pour tester nos différentes hypothèses. Ainsi, nous présentons d’abord une méthode permettant d’obtenir analytiquement l’ellipticité intrinsèque des galaxies naines. Les résultats de cette technique appliquée sur un échantillon de 25 satellites de la galaxie Andromède (M31) laissent présumer que le GL est plus perturbé qu’il n’était envisagé jusqu’alors. Après cette approche individuelle, nous exposons un résultat sur la cinématique globale du système M31. Cette estimation montre pour la première fois que la vitesse transverse de ce système par rapport à la Voie Lactée est élevée. Cela peut mener à de fortes implications sur le GL, notamment quant à la détermination de sa masse et de son évolution passée et future. / The Lambda-CDM cosmological model represents nowadays the best understanding of the formation and the evolution of large scale structures in our Universe. Nevertheless, this paradigm is not predictive and successful yet at smaller scales. In this context, satellites in the Local Group (LG), the simpler and closer galactic systems, are one of our best chance to test this model and to improve our comprehension of galaxy formation. Thus, we present here a method to derive analytically the intrinsic (3D) morphology of dwarf galaxies. Results of this technic applied to 25 Andromeda (M31) satellites suggest that the LG is in fact more disturbed than what was previously thought. After this individual approach, we further expose a recent result on the global kinematics of the M31 system. This new estimation suggests for the first time a high transverse velocity for this system with respect to the Milky Way. These values could lead to redefine the entire dynamic of the LG and its surroundings.

No description available.

Galaxy evolution depends on a diverse suite of factors, from the environment in which the galaxy exists to the number of supernovae that explode throughout its history. The structure and stellar populations present will also be altered by a galaxy's merger history, stellar mass, star formation rate, among other influences. Some factors, like mergers, are dependent on the environment of the galaxy, while others, like feedback from star formation, are intrinsic to the galaxy themselves. Dwarf galaxies are sensitive to many of these factors due to their smaller masses, hence shallower potential wells. Dwarfs are also interesting in themselves as the least massive structures that can form stars, forming the faint limit of galaxy types. There is some indication that the evolutionary pathway of dwarfs might be different than their more massive counterparts. Indeed, some dwarfs may be the stripped remnants of larger galaxy after a major interaction. Regardless, dwarfs are thought to be the building blocks of larger galaxies via hierarchical galaxy formation and understanding these small dwarfs helps us build a more complete picture of galaxy formation and evolution at all masses. As dwarfs generally have low stellar mass, they are very faint. Our most complete sample of dwarfs is therefore restricted to those that are nearby. These nearby systems are dominated by dwarfs satellite to the Milky Way and M31. However, the evolution of these satellites will be greatly influenced by their massive host. By studying nearby isolated dwarfs, we can try to separate the secular evolutionary processes of dwarfs from the influence of their larger host. Additionally, stellar populations can be resolved in these nearby galaxies, and so their structures can be probed to much fainter regimes than integrated light studies allow. The Sagittarius Dwarf Irregular Galaxy (Sag DIG) is one of the most isolated, low mass galaxies, located at the edge of the Local Group. Its isolation from other galaxies coupled with its relative proximity provide an excellent opportunity to study the intrinsic properties of this low mass system. We preform an in-depth analysis of its resolved stellar populations and its structural properties as the first galaxy in the larger dataset, Solitary Local Dwarfs Survey (Solo). Solo is a wide field photometric study targeting every isolated dwarf galaxy within 3 Mpc of the Milky Way. Solo is based on (u)gi multi-band imaging from CFHT/MegaCam for northern targets, and Magellan/Megacam for southern targets. All galaxies fainter than M ~ -18 (in the V band) situated beyond the nominal virial radius of the Milky Way and M31 (> 300 kpc) are included in this volume-limited sample, for a total of 42 targets. For Sag DIG, we provide updated estimates of its central surface brightness and integrated luminosity, and trace its surface brightness profile to a level fainter than 30 mag./sq.arcsec. Sag DIG is well described by a highly elliptical (disk-like) system following a single component Sersic model. However, a low-level distortion is present at the outer edges of the galaxy that, were Sag DIG not so isolated, would likely be attributed to some kind of previous tidal interaction. Further, we find evidence of an extremely low level, extended distribution of stars beyond ~5 arcmins (> 1.5 kpc) that suggests Sag DIG may be embedded in a very low density stellar halo. We compare the stellar and HI structures of Sag DIG, and discuss results for this galaxy in relation to other isolated, dwarf irregular galaxies in the Local Group. Sag DIG, and the similarly isolated dwarf Aquarius, both have HI distributions that are more circular than their stellar components. In contrast, Wolf - Lundmark - Mellote (WLM), another isolated but slightly more massive dwarf, has stellar and HI components that trace each other well. Sag DIG and Aquarius also differ in that there is no signature of rotation in the HI of Sag DIG, while there is clear rotation in both the HI and stellar component for Aquarius. These preliminary comparisons demonstrate some of the potential analysis which will be possible on a much larger scale with the full Solo Survey. / Graduate / 0606 / higgs@uvic.ca

Spatially-resolved studies of nearby star-forming galaxies are essential to understand various physical and chemical phenomena at play in the interstellar medium in the galaxies, and consequently to obtain a comprehensive picture of galaxy formation and evolution. In this thesis, I perform spatially-resolved analyses of chemical abundances and star-formation in nearby star-forming galaxies - blue compact dwarf galaxies (BCDs) and spiral galaxies. I map various properties of H II regions and the surrounding gas within three BCDs, using integral field spectroscopic (IFS) data from the Gemini Multi-Object Spectrograph-North. While answering questions related to chemical homogeneity, ionisation mechanisms and stellar populations within BCDs, I address more profound issues, which go beyond the characterisation of studied BCDs and aim to explain global phenomena with broader implications. The BCD NGC 4449 hosts a metal-poor central star-forming region, which I explain by various scenarios related to the interplay between star-formation, metal-distribution and gas dynamics within galaxies. The BCD NGC 4670 shows an unusual negative relationship between the nitrogen-to-oxygen ratio and oxygen abundance at spatially-resolved scales. I explore this relation with chemical evolution models and by comparison to other star-forming galaxies and suggest that nitrogen enrichment, variations in star-formation efficiency or hydrodynamical effects may be responsible for the observed relation. For another BCD, SBS 1415+437, the spatially-resolved abundances on average agree with the integrated abundance, implying that low-redshift spatially-resolved results may be directly compared with unresolved high-redshift results. I study spiral galaxies to address long-standing issues related to the reliability of metallicity calibrators and the Schmidt Law of star-formation. Using IFS data of twenty-four spiral galaxies taken with the Multi-Unit Spectroscopic Explorer, I find that the current strong-line metallicity calibrators for H II regions are unsuitable for regions dominated by diffuse ionised gas (DIG). I devise new recipes for estimating the metal-content of the DIG. For another set of nine spiral galaxies, I use multi-wavelength data to show that the spatially-resolved Schmidt relation is very sensitive to the consideration of diffuse background, which is a component unrelated to the current star-formation. Removal of this component from the SFR tracers and the atomic gas results in similar local and global Schmidt relation. To conclude, the spatially-resolved analyses presented in this thesis have led to discoveries and further questions, which I will address in my ongoing and future works.

This study focuses on the spatial distribution of the M31 satellite system. A new Bayesian technique for determining object distances from the Tip of their Red Giant Branch is developed and used to obtain distance probability distributions for M31and 27 of its satellite galaxies. These distances are then used to calculate the satellite positions in three dimensions. Subsequent analysis of the resulting spatial distribution reveals striking inhomogeneity, with roughly half of the satellites confined to a curiously oriented thin disk. The distribution is also markedly asymmetric, with the majority of satellites lying on the Milky Way side of M31.

The study of dwarf galaxies is important in order to better understand the physics of the young universe and how larger galaxies form and evolve. In this work we focus on Blue Compact Galaxies (BCGs) which havemuch enhanced star formation (starbursts), causing blue colours and strong emission line spectra. Investigating of the inner motions of BCGs provides a means for determining masses and understanding what triggered the current starburst. We have used the Very Large Telescope to perform challenging observations of the stellar motions in several BCGs, as seen in the near-infrared Ca-triplet absorption lines. By comparing these to the kinematics of the ionized interstellar medium, we were able to look into the role of feeback from stellar winds and supernova explosions, as well as further strengthen the notion that the merging of galaxies plays an important role. Spatially resolved spectroscopy can yield information about the 3D-structure of galaxies. We have used a Fabry-Perot interferometer to study the kinematics of the interstellar medium in two samples of galaxies, each containing about twenty objects. We find strong indications for ongoing galaxy mergers that correlate well with the strength of the star-formation activity. Furthermore, by estimating dynamical masses, BCGs are shown to be on average not dynamically supported by rotation. In addition, we have used data from the Sloan Digital Sky Survey to study the frequency of starbursts in the local universe and the connection to their descendants. We selected starbursts by the strength of emission in H-alpha, the first Balmer recombination line, and post-starbursts by the strength of absorption in H-delta. These are indicators of currently ongoing and recent, on the order of 100 Myr, star-formation, respectively. By modelling the stellar populations we derive ages and masses and can establish a link between starbursts and postbursts in a time sequence. We find that starbursts are active on a 100 Myr timescale but are rare objects in the local universe.

Cette étude concerne le distribution spatiale du système des satellites de M31. Une nouvelle technique bayésienne pour la détermination des distances d'objets basé sur le point-final des magnitudes des géants Rouges a été développé et utilisé pour obtenir des distributions de probabilité à distance pour les M31 et 27 de ses galaxies satellites. Ces distances sont ensuite utilisés pour calculer les positions des satellites en trois dimensions. Une analyse ultérieure de la distribution spatiale qui en résulte révèle hétérogénéité frappante, avec près de la moitié des satellites confinés à un disque curieusement orienté mince. La distribution est aussi fortement asymétrique, avec la majorité des satellites se trouvant sur le côté de la Voie Lactée M31. / This study focuses on the spatial distribution of the M31 satellite system. A new Bayesian technique for determining object distances from the Tip of their Red Giant Branch is developed and used to obtain distance probability distributions for M31and 27 of its satellite galaxies. These distances are then used to calculate the satellite positions in three dimensions. Subsequent analysis of the resulting spatial distribution reveals striking inhomogeneity, with roughly half of the satellites confined to a curiously oriented thin disk. The distribution is also markedly asymmetric, with the majority of satellites lying on the Milky Way side of M31.