We present the discovery of a very faint stellar system, SMASH 1, that is potentially a satellite of the Large Magellanic Cloud. Found within the Survey of the MAgellanic Stellar History (SMASH), SMASH 1 is a compact (r(h) 9.1(-3.4)(+5.9)pc) and very low luminosity (M-V = -1.0 +/- 0.9, L-V = 10(2.3 +/- 0.4) L-circle dot) stellar system that is revealed by its sparsely populated main sequence and a handful of red giant branch candidate member stars. The photometric properties of these stars are compatible with a metal-poor ([Fe/H] = -2.2) and old (13 Gyr) isochrone located at a distance modulus of similar to 18.8, i.e., a distance of similar to 57 kpc. Situated at 11 degrees.3 from the LMC in projection, its three-dimensional distance from the Cloud is similar to 13 kpc, consistent with a connection to the LMC, whose tidal radius is at least 16 kpc. Although the nature of SMASH 1 remains uncertain, its compactness favors it being a stellar cluster and hence dark-matter free. If this is the case, its dynamical tidal radius is only less than or similar to 19 pc at this distance from the LMC, and smaller than the system's extent on the sky. Its low luminosity and apparent high ellipticity (epsilon = 0.62(-0.21)(+0.17)) with its major axis pointing toward the LMC may well be the tell-tale sign of its imminent tidal demise.

Four regions of massive star formation in the Large Magellanic Cloud (LMC) were observed for water and methanol maser emission and radio continuum emission. A total of 42 radio detections were made including 27 new radio sources, four water masers, and eight compact HII regions. The lobes of a radio galaxy were resolved for the first time, and the host galaxy identified. Seven sources were associated with known massive young stellar objects (YSOs). A multi-wavelength analysis using both the infrared and radio spectrum was used to characterize the sources. Mid-infrared color-magnitude selection criteria for ultracompact HII (UCHII) regions in the LMC are presented, yielding 136 UCHII region candidates throughout that galaxy. New maser detections identified two previously unknown massive YSOs. No methanol masers were detected, consistent with previous studies and supporting the hypothesis that the LMC may be deficient in these molecules. These discoveries contribute to the history of star formation in the LMC, which will lead to a better understanding of star formation in the Milky Way and throughout the universe.

The Magellanic System at a distance of 50 kpc from the Milky Way (MW), is a prime target in the study of stellar populations, star formation histories and galactic dynamics in low metallicity environments. The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) have been observed in great depth, however there has been somewhat less interest in the Magellanic Bridge connecting the two and only more recently has the interest surged in the Magellanic Stream, which trails the Clouds between them and the MW. The Magellanic Bridge has a known younger stellar population dating back to Irwin’s observations (Irwin et al., 1990), only more recently has an older population been confirmed in the Bridge by Bagheri et al. (2013) and No¨el et al. (2013), while the Magellanic Stream is known to contain gas only with no stellar component. The estimated ages of the Bridge and Stream are 200 Myr (Bekki, 2007) and 2 Gyr (Diaz and Bekki, 2012) respectively, with the postulated Bridge formation from a tidal interaction between the Clouds. The formation of the Stream is less well understood with different models using varying assumptions and parameters such as Besla et al. (2012) and Nidever et al. (2010), including possibilities that the Clouds were historically bound or un-bound, and that the MW may or may not have been involved in the Stream formation. The work in this thesis makes use of different methods of removing the Galactic foreground population in the direction of the Magellanic Bridge and Stream to create cleaned catalogues of these regions. Various methods of analysis are applied to the cleaned catalogues in this work to identify stellar populations in the Bridge and Stream and density variations in the Bridge, including the production of CMDs and two-colour diagrams, fitting isochrones to the observational data, creating stellar density maps and studying spatial variations. This work contains the first published confirmation that the Bridge contains an older population of stars from public catalogues, which is supported with observations of the older population in recent deeper surveys, and confirmed with spectroscopic follow up observations. The young population has ages within the age of the Bridge ( 200 − 500 Myr) and are likely to have formed in-situ, in regions of high density gas closest to the SMC. The number of young blue objects in the Bridge tiles is greater towards the SMC and decreases towards the LMC. Populations identified here reach ages up to 3 Gyr are likely to have been drawn into the Bridge from the Clouds at formation. The key results from this work are that an older Bridge stellar population has been identified and confirmed, indicating that stars as well as gas were drawn into the Bridge at its creation. The fact that the younger population has the highest density away from the main concentration of hydrogen show that the gas within the Bridge has been displaced by ram pressure, most likely due to the Clouds moving through the Galactic halo. Less concrete results in this work reveal a puzzling populetion of objects within the Magellanic Stream, which could be stellar in nature and with follow up work, could be the first observation of Stream objects. This work contributes to our understanding of the interaction between the LMC and SMC via the Stellar populations between them.

In this paper, we introduce the Local Volume TiNy Titans sample (LV-TNT), which is a part of a larger body of work on interacting dwarf galaxies: TNT . This LV-TNT sample consists of 10 dwarf galaxy pairs in the Local Universe (< 30 Mpc from Milky Way), which span mass ratios of M-*,M- 1/M-*,M- 2 < 20, projected separations < 100 kpc, and pair member masses of log(M-*/M-aS (TM)) < 9.9. All 10 LV-TNT pairs have resolved synthesis maps of their neutral hydrogen, are located in a range of environments and captured at various interaction stages. This enables us to do a comparative study of the diffuse gas in dwarf-dwarf interactions and disentangle the gas lost due to interactions with haloes of massive galaxies, from the gas lost due to mutual interaction between the dwarfs. We find that the neutral gas is extended in the interacting pairs when compared to non-paired analogues, indicating that gas is tidally pre-processed. Additionally, we find that the environment can shape the H i distributions in the form of trailing tails and that the gas is not unbound and lost to the surroundings unless the dwarf pair is residing near a massive galaxy. We conclude that a nearby, massive host galaxy is what ultimately prevents the gas from being re-accreted. Dwarf-dwarf interactions thus represent an important part of the baryon cycle of low-mass galaxies, enabling the 'parking' of gas at large distances to serve as a continual gas supply channel until accretion by a more massive host.

The next generation of ground-based optical/infrared (IR) telescopes will have primary mirrors of up to 42 m. To take advantage of the large potential increase in angular resolution, adaptive optics will be essential to overcome the resolution limits set by atmospheric turbulence. Novel techniques such as Multi-Conjugate Adaptive Optics (MCAO) and Multi-Object Adaptive Optics (MOAO) are being developed to achieve near diffraction-limited images over large fields-of-view. This thesis concerns the development of MCAO and MOAO pathfinders. Specifically, the construction of CANARY, aMOAO demonstrator, and the on-sky performance and scientific exploitation of the Multi-conjugate Adaptive optics Demonstrator (MAD). CANARY is under construction for the William Herschel Telescope (WHT) in La Palma and contains a telescope simulator to allow testing of the set-up in the laboratory. The simulator contains a natural guide star emulator, turbulence phase screens, and telescope relay optics. The work presented here concerns the integration of the various components in relation to numerical models and the CANARY specifications. MAD was a near-IR imager on the Very Large Telescope (VLT) in Chile. Science demonstration observations were taken of R136, the young, massive cluster situated in the 30 Doradus star-forming region in the Large Magellanic Cloud. These data were used here to determine the MCAO performance across the ~1’x1’ field-of-view, for different pointings with respect to the guide stars, finding high Strehl ratios and relatively uniform corrections across the fields. The MAD data are then used to construct radial surface brightness profiles for R136, providing new insights into intriguing past results from the Hubble Space Telescope. The MAD data reveal that the profile is strongly asymmetric, removing the need for dramatic dynamical evolution of the cluster in the recent past, and highlighting the importance of considering asymmetries when analysing clusters further afield. The MAD data, combined with other near-IR imaging from the VLT, are then used to investigate the nature of candidate young stellar objects from recent observations with the Spitzer Space Telescope.

We examine a diffuse emission region near the center of SNR 0509-67.5 to determine its nature. Within this diffuse region we observe a point-like source that is bright in the near-IR, but is not visible in the B and V bands. We consider an emission line observed at 6766 angstrom and the possibilities that it is Ly alpha, H alpha, and [O II] lambda 3727. We examine the spectral energy distribution (SED) of the source, comprised of Hubble Space Telescope B, V, I, J, and H bands in addition to Spitzer/IRAC 3.6, 4.5, 5.8, and 8 mu m bands. The peak of the SED is consistent with a background galaxy at z approximate to 0.8 +/- 0.2 and a possible Balmer jump places the galaxy at z approximate to 0.9 +/- 0.3. These SED considerations support the emission line's identification as [O II] lambda 3727. We conclude that the diffuse source in SNR 0509-67.5 is a background galaxy at z approximate to 0.82. Furthermore, we identify the point-like source superposed near the center of the galaxy as its central bulge. Finally, we find no evidence for a surviving companion star, indicating a double-degenerate origin for SNR 0509-67.5.

Neste projeto de pesquisa planeja-se obter indícios da correlação entre o conteúdo metálico estelar deduzido para a Via Láctea e os indíces metálicos obtidos para as Nuvens de Magalhães. O ponto de apoio para tal comparação é que cada encontro deixará importantes traços na eficiência de formação dos membros do tripleto. À medida que os encontros dependem da história dinâmica, suas ``impressões digitais\'\' deixadas nos conteúdos estelares colocam importantes limitações na história dinâmica e vice-versa. Para tanto, são utilizados os dados espectroscópicos já obtidos com o telescópio Magellan Clay, para uma amostra contendo 28 estrelas ricas em carbono encontradas nas Nuvens de Magalhães. A quantidade de carbono bem como a existência ou não de binaridade nas estrelas da amostra são indícios das possíveis fontes da sobreabundância do carbono. A caracterização da amostra é essencial para o estudo da relação entre duas populações estelares aparentemente distintas: a de estrelas de carbono e a de estrelas pobres em metais enriquecidas em carbono. Para tanto, são utilizados catálogos de espectros assim como critérios fotométricos. A descoberta de alguma relação entre as duas populações pode ajudar a esclarecer o problema dos processos de enriquecimento de carbono, notado nas atmosferas estelares. A futura determinação dos parâmetros físicos das estrelas que compõem a amostra pode revelar detalhes sobre a história de formação estelar dos objetos das Nuvens e, portanto, vincular a evolução dessas duas galáxias-satélites à história da Via Láctea. / This project searches for signs of correlation between metallic stellar content, available for the Milky Way, and the metallicities indices obtained for the Magellanic Clouds. This comparison is supported by the traces on the formation of these three galaxies, that should have been left by each triplet members encounter. Since these crosses depend on the dynamical history, their fingerprints left by stellar content can estabilish constraints to the Galactic dynamical history. Spectroscopic data for a sample of carbon stars, obtained on the Magellanic Telescope, are used in this work. The amount of carbon, as the existence or not of binary stars in this sample, indicates possible sources of this element. The determination of sample properties is essential for studying the constraints between two stellar populations that are apparently distincts: carbon stars and carbon enhanced metal-poor stars. To do this, spectral catalogues and photometric criteria are used. Finding the correlations between both populations will bring some light to the unknown carbon enrichment processes that occured at the stellar atmospheres. Variability, emission lines, and binarity are studied for the sample. Stellar parameters are discussed, although there is no method applicable to this sample. By estimating the physical parameters of the stars presented in this sample and by analysing their carbon abundances, one can provide hints of the star formation history of objects in the Magellanic Clouds and therefore constraint the evolution of these satellite-galaxies to the Milky Way.

High Mass X-Ray Binary Stars (HMXBs) are stars that contain one early-type main sequence or giant star and one of a black hole, neutron star or white dwarf. HMXBs in the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are instructive to study because both galaxies are metal poor in compari- son to the Milky Way and they are fairly transparent to both optical and X-ray radiation. This allows a more complete study of the whole population, without the biasing effects of gas and dust that occur in our own Galaxy. The objective of this study was to find the periods of HMXBs in the LMC and SMC with known optical counterparts in the dataset acquired by the Robotic Optical Transient Search Ex- periment telescope. Two possible orbital periods were found for the objects XTE J0055-724 and RX J0101.3-7211 of 1724 days and 478 days, respectively. Continued observations are recommended to conrm the two periods.

High Mass X-Ray Binary Stars (HMXBs) are stars that contain one early-type main sequence or giant star and one of a black hole, neutron star or white dwarf. HMXBs in the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are instructive to study because both galaxies are metal poor in compari- son to the Milky Way and they are fairly transparent to both optical and X-ray radiation. This allows a more complete study of the whole population, without the biasing effects of gas and dust that occur in our own Galaxy. The objective of this study was to find the periods of HMXBs in the LMC and SMC with known optical counterparts in the dataset acquired by the Robotic Optical Transient Search Ex- periment telescope. Two possible orbital periods were found for the objects XTE J0055-724 and RX J0101.3-7211 of 1724 days and 478 days, respectively. Continued observations are recommended to conrm the two periods.

O objetivo desta tese é analisar aspectos do sistema de satélites da Via Láctea de relevância cosmológica. Dentre estes aspectos destacam-se dois: o censo de satélites da Galáxia – onde constata-se que a quantidade destes objetos é muito inferior ao predito por modelos cosmológicos do tipo Matéria Escura Fria – e a frequência anômala de satélites luminosos, como a Pequena e Grande Nuvem de Magalhães (SMC e LMC respectivamente). Além disso, a determinação dos parâmetros estruturais da LMC pode impor vínculos a sua formação, histórico orbital e sobre a massa de nossa Galáxia. Neste trabalho é desenvolvida uma técnica de busca por satélites da Via Láctea. Esta técnica foi otimizada para utilizar dados da nova geração de grandes surveys de maneira eficiente. Este código, o FindSat, foi validado em uma amostra de galáxias anãs conhecidas e se mostrou eficiente em detectar as galáxias anãs mais tênues de que se tem registro. A aplicação desse código a uma região do Sloan Digital Sky Survey (SDSS) ainda não explorada nesse sentido revelou uma série de candidatos a novos satélites. Foram selecionados os candidatos mais promissores para observação de follow-up. Estas observações revelaram que um destes candidatos é de fato um novo satélite da Via Láctea. Este novo objeto é muito provavelmente um aglomerado globular do halo em estágio avançado de dissolução, porém, seu tamanho e magnitude integrada colocamno em um domínio limítrofe entre aglomerado e galáxia anã. Através da cuidadosa análise dos demais candidatos, constatou-se que nenhum outro é de fato um novo satélite da Galáxia. Além disso, foi realizado o estudo do perfil de densidade e geometria da LMC. Este estudo utilizou dados de verificação científica do Dark Energy Survey (DES). Constatase que o perfil de densidades para estrelas jovens (< 3 Gyr) possui um raio de escala cerca de 50% menor que o da população velha (> 3 Gyr), favorecendo o cenário de formação tipo outside-in. O estudo da extensão da componente estelar da LMC revela um raio de maré de cerca de 18 kpc, permitindo o cálculo da massa dinâmica total da LMC. O valor de massa obtido favorece a hipótese onde as Nuvens de Magalhães estariam por sua primeira passagem pelo perigaláctico. Além disso, a distância heliocêntrica e espessura do disco da LMC foram determinadas utilizando estrelas do Red Clump (RC). Notou-se que regiões no extremo norte da LMC estão sistematicamente mais próximas de nós do que o esperado, este efeito evidencia o warp no disco dessa galáxia. Observou-se que a espessura do disco aumenta na periferia da LMC, caracterizando o fenômeno de flare. O aumento na espessura juntamente com a maior extensão da população velha da LMC é interpretado como a presença de dois componentes discoidais. Esta é a primeira evidência desse tipo baseada apenas em métodos de contagem de estrelas. / The goal of this thesis is to analyse comologically relevant aspects of the Milky Way (MW) satellite system. Among these we may highlight two: the census of MW satellites – where the observed number of these objects is much less than what is expected by Cold Dark Matter (CDM) models – and the anomalous frequency of luminous satellites, such as the Small and Large Magellanic Clouds (SMC and LMC respectively). Besides the cosmological importance of the Clouds, the determination of its structural parameters may help to constraint models for their formation, orbital history, and ultimately the mass assembly in our Galaxy. In this work a technique to search newMWsatellites is developed. This technique was optimized to run efficiently on large datasets, such as the ones being generated by the new generation of surveys. The code, FindSat was validated in a sample of well known MW satellites and has proven to be well succeeded even for the most faint of these objects. The application of this code to an unexplored region of the Sloan Digital Sky Survey (SDSS) revealed a large amount of new dwarf galaxy candidates, some of which where selected for follow-up observation. These observations led to the discovery of a new MW satellite. This new object is most likely a globular cluster in an extreme stage of dissolution. However, its integrated magnitude and size makes it difficult to discern it from a dwarf galaxy. By a careful analysis of the remaining candidates, it was shown that no other new satellite was in the sample. The density profile and geometry of the LMC was also analysed. This study used the recent science verification data from the Dark Energy Survey (DES). It was found that the density profile for young stars (< 3 Gyr) has a scale radius 50% smaller when compared to the one obtained for older stars (> 3 Gyr). This result favours the outsidein galaxy formation scenario. The total extension of the LMC stellar component was measured, allowing the estimate of a truncation radius of about 18 kpc. Assuming that this truncation has tidal origins the dynamical mass of the LMC is inferred. The mass value found favours the case for the first perigalactic passage of the Clouds. Besides that, the heliocentric distance and thickness of the LMC disk was determined using Red Clump (RC) stars. Evidence for warp was found in the North edge of the LMC, in the sense that the disk is systematically more distance than expected. While the thickness of the disk increases towards the outer parts of the LMC, which is a phenomena known as flare. This effect joined with the fact that the older LMC stellar population is more extended, favours the presence of two disk components in this galaxy. This is the first evidence of this kind based only on star counts.