So often in astronomy, an object is not considered for its individual merits, but for what we may learn from its properties regarding some larger population. The existence of dark matter is a prime example of this; we cannot see it directly but we can infer its presence by noting its effects on the stars orbiting within its potential. This thesis describes how various sets of tracer populations can be used to probe the properties of a variety of galaxies in the Local Group. I begin by describing the extraction of a variable catalogue from the Sloan Digital Sky Survey Stripe 82 dataset and then use the catalogue to select a high-quality set of RR Lyrae stars. Analysing the distribution of the RR Lyraes reveals three significant substructures in the Milky Way halo: the Hercules-Aquila Cloud and the Sagittarius Stream, which were already known to exist, and the Pisces Overdensity, which was previously undetected. It is a faint, extended structure found at ~80 kpc and is of unknown origin. Altogether, I find that nearly 80% of the RR Lyraes are associated with substructures, consistent with the theory that galaxy halos are predominantly, or even entirely, made up from disrupted satellites. I also investigate the density distribution of RR Lyraes in the halo, finding that it is best fit by a broken-power-law model, in good agreement with previous work. I go on to develop a set of tracer mass estimators that build on previous work which make use of actual (and not projected) distance and proper motion data, reflecting the amount and quality of data now available to us. I show that proper motion data is, in theory, very useful and can greatly increase the accuracy of the mass estimates; in practice, however, current analysis is hampered by the large errors inherent in the proper motion data. The results are also subject to mass-anisotropy degeneracy, which current data is not yet able to break. Nevertheless, I am able to estimate the mass of the Milky Way to be M = 2.7 ± 0.5 x 10¹² Msun and the mass of M31 to be M = 1.5 ± 0.4 x 10¹² Msun. Andromeda XII and Andromeda XIV are two M31 satellites that have been dubbed 'extreme' and are thought to be on first infall into the M31 system. I modify the classical Timing Argument so that it can be applied to two external galaxies and then apply it to M31 and each of And XII and And XIV in turn to investigate the properties of their orbits. I then run a series of Monte Carlo simulations to investigate how likely such satellites are to exist and conclude that they are not as unusual as previously believed. Finally, I discuss three upcoming wide-field, all-sky surveys and their implications for the future of the study of the Local Group.

Until recently, obtaining rest-frame optical spectra of galaxies at z > 1 was a time consuming and challenging observation due to the difficult nature of near-infrared (near-IR) spectroscopy. However, with the advent of second generation ground-based near-IR spectrographs (e.g. KMOS, MOSFIRE), and the new low resolution near-IR grisms on the Hubble Space Telescope (HST), we have entered a new era in the study of high redshift galaxies. This thesis explores the physical properties of star-forming galaxies in the redshift range 1 < z < 3 by utilising a custom reduction of the 3D-HST near-IR grism spectroscopic survey. One of the most important observational constraints on the evolution of galaxies is the mass-metallicity relation (MZR), which is sensitive to both the star-formation history and various inflow/outflow processes. I use the 3D-HST spectra to provide a new constraint on the MZR at 2:0 < z < 2:3, and moreover measure the O/H abundance directly from the oxygen and hydrogen emission lines ([OII], [OIII] and Hβ) as opposed to the more common method at high redshift of inferring O/H from the N/H ratio (via [NII] and Hα). I show that the traditional form of the MZR is recovered from the 3D-HST data, with metallicity increasing with the stellar mass of a galaxy. However, the absolute metallicity values I derive are inconsistent with previous N/H-based measurements of metallicity at these redshifts. Moreover, I show that the 3D-HST data is inconsistent with the `fundamental metallicity relation' (FMR), and that, contrary to previous claims, this local Universe relation may not hold out to z & 2. To investigate this metallicity discrepancy further, I measure the evolution of the [OIII]/Hβ nebular emission line ratio in the 3D-HST spectra over the redshift range 1:3 < z < 2:3. I compare this observed line ratio evolution with state-of-the- art theoretical models which take into account the independent evolution of the ionization parameter, electron density and metallicity of star-forming regions with redshift. The homogeneous 3D-HST dataset allows me to perform a consistent analysis of this evolution which takes into account line luminosity selection effects. I show that, according to models, the observed [OIII]/Hβ evolution cannot be accounted for by pure metallicity evolution. Instead I am able to infer that the line ratio evolution is more consistent with, at the very least, an evolution to stronger ionizing conditions at high redshift, and perhaps even denser star-forming regions. I explore how this result can also explain the observed discrepancy between high redshift metallicity measurements. In light of this finding, I revisit the MZR at z >~ 2 and employ a purely theoretical approach to inferring metallicities from nebular lines, which is able to account for an evolution in ionization conditions. I then use a selection of galaxies from the local Universe, which mimic the properties of high redshift galaxies, to derive a more robust ionization sensitive, conversion, between N/H and O/H. With this new conversion which I am able to bring the previous inconsistent metallicity measurements at z >~ 2 back into agreement. Finally, I am able to show that, in this new formalism, the metallicity evolution between z = 2 and z = 3 is perhaps not as large as previously reported. To conclude I discuss ongoing work as part of the KMOS Deep Survey (KDS) being undertaken with the near near-IR Multi-Object Spectrograph KMOS on the VLT. I describe the observations and data reduction that has been completed to date and describe how this instrument will allow me to extend the work presented in this thesis to z > 3. I also introduce FIGS, a new HST near-IR grism survey seeking to spectroscopically identify galaxies at 5:5 < z < 8:5 and work I have begun in exploring this dataset.

No description available.

Due to the finite speed of light and a vast, expanding universe, telescopes are just now receiving the light emitted by galaxies as they were forming in the very early universe. The light from these galaxies has been redshifted (stretched to longer, redder wavelengths) as a result of its journey through expanding space. Using sophisticated techniques and exceptional multi-wavelength optical and infrared data, we isolate a population of 378 galaxies in the process of formation when the Universe was only two billion years old. By matching the distinctive properties of the light spectra of these galaxies to models, the redshift, age, dust content, star formation rate and total stellar mass of each galaxy are determined. Comparing our results to similar surveys of galaxy populations at other redshifts, a picture emerges of the growth and evolution of massive, star-forming galaxies over the course of billions of years.

L'âge des galaxies est un paramètre crucial dans le cadre des modèles de formation et d'évolution des galaxies. Ma thèse se base sur l'étude de cette quantité physique dans le cadre du sondage profond de VIMOS (VUDS). Ce sondage permet d'étudier les galaxies dans l'univers jeune et de remonter au moment où il était agé de seulement quelques centaines de millions d'années. Durant ce doctorat, j'ai pu prendre part au traitement des données de ce sondage et j'ai été responsable de l'ensemble de la correction des spectres du sondage. J'ai également modifié et amélioré le logiciel GOSSIP qui est un logiciel d'ajustement de modèle de galaxie permettant d'extraire les paramètres physiques des galaxies. L'utilisation de ce logiciel m'a permis d'étudier l'extinction par le milieu intergalactique des galaxies ainsi que leurs âges. Ceci m'a permis d'étudier l'époque de formation des galaxies ainsi que l'évolution du paramètre de Hubble. / Age of galaxie is a crucial parameter in the framework of galaxy formation and evolution. This thesis is based on the study of this parameter in the framework of the VIMOS Ultra Deep Survey. This galaxy survey allows to study galaxies when the universe was young and to go back when it was few hundreads of million years old. During this PhD I could take part of the data processing and I was responsible of all the spectroscopic corrections. I also implemented and improved the GOSSIP software. This software is a template fitting program that allows the extraction of galaxy physical parameters. The use of this software allowed me to study the extinction of the Inter Galactic medium (IGM) as well as their ages. I could then study the epoch of galaxy formation and the evolution of the Hubble parameter

This thesis explores the topic of maximum mass stability of neutron stars. The outer structure is detailed and explores nuclear pasta phases, the neutron drip line, and density transitions of matter in the crust and atmosphere layers. Other discussion points include superfluids in the crust and core, vortex roles in neutron stars, and magnetic field effects on the EOS in neutron stars. The inner core is studied in much more detail due to its significant role in EOS. The variety of stars include pion condensate stars, kaon condensate stars, npeu stars, npeu stars with the inclusion of hyperons, quark-hybrid stars, and strange stars. Included with these is a description of nucleon-nucleon, nucleon-nucleon-nucleon interactions, the appearance factors that affect hyperon species, and the formation process of kaons, pions, quarks, and hyperons. The ending EOS are compared with their maximum mass values to determine which ones are likely to limit the mass of neutron stars.

Nesta tese, investigamos a discrepância existente entre o número de galáxias satéli-tes da Via Láctea que é previsto e aquele que é observado, questão conhecida como ``problema da falta de satélites\'\' (PFS). Este problema pode ser reformulado em termos de um desacordo entre a função de luminosidades das galáxias satélites (FLS) que é estimada a partir de dados observacionais e a FLS predita por modelos numéricos de formação de galáxias. Nós revisamos tanto propriedades observacionais da população de satélites quanto a teoria associada à modelagem da formação de galáxias e estruturas. Para abordar o PFS, estudamos diferentes soluções possíveis. Nós desenvolvemos uma modificação simples ao potencial do inflaton usual e mostramos que esta leva a uma redução no número de halos de matéria escura de pequena massa. Nós usamos, então, um modelo semi-analítico de formação de galáxias para confirmar que supressões similares do espectro de potências de pequena escala produzem uma FLS com a forma correta. Em uma outra direção, nós discutimos outros mecanismos astrofísicos capazes de reduzir o número de galáxias pequenas, especificamente: os ventos gerados por explosões de supernovas e o aquecimento do meio intergalático durante a reionização do Universo. Finalmente, nós estudamos como um campo magnético primordial pode influenciar a formação de galáxias de pequena massa. Para isso, nós inicialmente mostramos que a pressão devida a um campo magnético leva a uma alteração significativa na massa de filtragem, levando a uma importante supressão na acresção de gás por galáxias de baixa massa. Introduzindo estas modifi-cações em um modelo numérico de formação de galáxias, mostramos que, para valo-res realistas de intensidade de campo, a pressão devido ao campo magnético leva a um bom acordo entre a FLS prevista e observada. / In this thesis we investigate the discrepancy between the predicted and observed number of satellite galaxies in the Milky Way, known as ``the missing satellites problem\'\' (MSP). This problem can be translated into the disagreement between the satellite luminosity function (SLF), which is estimated from the observational (particularly the SDSS) data and the SLF predicted by numerical models of galaxy formation. We review both the observational properties of the satellite population and the essentials of galaxy and structure formation modelling. To tackle the MSP, we study different possible solutions. We develop a small modification to the usual chaotic inflaton potential and show that it leads to a reduction in the number of small mass haloes. We use a semi-analytic model of galaxy formation to confirm that suppressions of the small scale power spectrum can produce a SLF with the correct shape. In a different direction, we discuss other astrophysical mechanisms that can reduce the number of small mass galaxies, namely: the outflows generated by supernovae explosions and the heating of the intergalactic medium during the reionization of the Universe. Finally, we study how a primordial magnetic field can influence the formation of small mass galaxies. We first find that small primordial magnetic field significantly change the filtering mass, leading to an important suppression in the gas accretion by small mass haloes. ( The filtering mass is the mass for which the baryon accretion is reduced to approximately 1/2 its normal value.) Introducing these modifications in the galaxy formation model, we show that for realistic field strengths, the pressure due to the magnetic field can result in a good match between the observed SLF and the model predictions.

Este trabalho constituiu-se da análise de abundâncias químicas de nebulosas planetárias localizadas na conexão bojo-disco, onde se dá o encontro das características do bojo, tais como a diversidade de abundâncias, com as do disco, tais como o limite interno do gradiente radial de abundâncias. Em particular, o estudo de nebulosas planetárias nesta região traz informações importantes a respeito das abundâncias de elementos tais como He, O, Ne, Ar, S e de sua evolução associada à evolução das estrelas de massa intermediária. Novas abundâncias foram derivadas a partir de observações espectrofotométricas no telescópio Perkin-Elmer de 1.60 m do Laboratório Nacional de Astrofísica (LNA) em Minas Gerais, Brasil. Foram observadas nebulosas planetárias selecionadas através da localização na direção do centro da Galáxia, diâmetro angular no óptico e fluxo em rádio. A comparação entre as abundâncias obtidas neste trabalho com outros trabalhos da literatura mostrou que as distribuições das abundâncias são compatíveis. Para o estudo da distribuição das abundâncias na conexão utilizou-se as escalas de distância de Maciel & Pottasch (1980), Cahn et al. (1992) e Zhang (1995). A separação das nebulosas planetárias do bojo e do disco mostrou que em média as do bojo apresentam menores abundâncias se comparadas as disco interno, para as escalas de Cahn et al. (1992) e Zhang (1995). Contudo esta separação não é superior aos erros na obtenção das abundâncias, indicando apenas uma tendência. Através deste estudo encontrou-se uma distância de separação entre as propriedades químicas destas regiões. Para a primeira escala esta distância é de 2.9 kpc e para a segunda de 1.5 kpc. Sendo que o valor de 2.9 kpc concorda com resultados independentes. A escala de Maciel & Pottasch (1980) não apresentou resultados conclusivos a respeito da distribuição das abundâncias entre estas estruturas. / This project consisted in a spectrophotometric investigation of planetary nebulae located at the bulge-disk connection of the Milk Way, where the bulge and disk characteristics such as chemical and kinematic properties should intersect. In particular, the study of planetary nebulae in the bulge-disk connection brings important informations about the chemical abundances of elements such as He,N,O,S,Ar,Ne and the evolution of these abundances, associated with the evolution of intermediate-mass stars, as well as for the chemical evolution of the Galaxy. New abundances were derived from spectrophotometric observations at the Perkin-Elmer 1.6 m telescope of Laboratório Nacional de Astrofísica - Brazil. The objects were selected according to their location toward the Galactic center, angular diameter, and radio flux. The data show a good agreement with some other results in the literature, in the sense that the distribution of the abundances is similar to those works. Statistical distance scales from Maciel & Pottasch (1980), Cahn et al. (1992), and Zhang (1995) were used to study the distribution of chemical abundances in the bulge-disk connection. Making use of Cahn et al. (1992) and Zhang (1995) scales, the separation between PNe belonging to the disk and bulge showed that on the average those from the bulge have a slight underabundance compared to those from the inner disk. Nevertheless this separation is not larger than the errors in the abundance determinations, showing only a tendency. This study allowed to find the distance in which the chemical properties of these regions are distinct. For the former scale the distance is 2.9 kpc and for the latter is 1.5 kpc. The value of 2.9 kpc agree with other results for the disk-bulge separation. The same study with Maciel & Pottasch (1980) distance scale did not show any conclusive result about the distribution of chemical abundances between these structures.

Entender como as galáxias se formam e evoluem ao longo do tempo é um dos maiores desafio da cosmologia moderna. Vários processos estão presentes na formação de galáxias, tais como o feedback de supernovas e núcleos galácticos ativos, evolução química e dinâmica, e também efeitos ambientais. Esta tese abrange estes processos, a partir de um ponto de vista observacional. A Via Láctea tem um papel fundamental na compreensão dos vários processos envolvidos na formação de uma galáxia, e começamos nosso projeto estudando nossa própria galáxia. Diferentes processos deixam assinaturas típicas na distribuição de velocidades e metalicidades das estrelas. Por esta razão, combinando cinemática e abundâncias químicas, foi possível determinar a origem de uma amostra de estrelas velhas e ricas em metais. Compreender como e onde essas estrelas se formaram está intimamente relacionado com mecanismos presentes na evolução do disco Galáctico. Apesar de não podermos observar estrelas individuais em galáxias distantes, somos capazes de inferir a história de formação destas galáxias combinando modelos de população estelar simples, de forma a reproduzir o espectro observado. Usando esta metodologia, foi possível traçar a história de formação estelar de galáxias elípticas, e dessa forma restringir os mecanismos de feedback que regulam a formação de estrelas em halos. No cenário Lambda-CDM, as estruturas menores são formadas primeiro, e então elas se agrupam, formando assim estruturas cada vez maiores. As galáxias, ao serem incorporadas à sistemas maiores, sofrem os efeitos de diversos processos que atuam em ambientes de alta densidade, mudando assim suas propriedades. Desta forma, a evolução das galáxias e a formação de estruturas em grande escala andam lado a lado, como mostramos em nosso estudo de propriedades de galáxias em grupos. Exploramos a distribuição espacial das galáxias na vizinhança de grupos, e também usamos a distribuição de velocidades das galáxias para determinar o estágio evolutivo do grupo. Foram encontradas correlações importantes entre o estágio evolutivo do grupo e as populações de galáxias que nestes residem. / Understanding the way galaxies form and evolve throughout the cosmic time remains one of the greatest challenges of modern cosmology. Several processes are known to play a role in the formation of galaxies, such as feedback from supernovae and active galactic nuclei, chemical and dynamical evolution and environmental effects. This thesis encompasses these processes, from an observational point of view. The Milky Way plays a pivotal role in understanding the various processes involved in the formation of a galaxy, and we start our understanding program by studying our own Galaxy. Different formation processes leave typical signatures in the velocity and metallicity distribution of stars. For this reason, we were able to trace the origin of old and metal-rich stars by combining their kinematics and chemical abundances. Understanding how and where these stars were formed is closely related to mechanisms driving the evolution of the Galactic disk. Although we cannot observe individual stars in distant galaxies, only the integrated spectra, we are able to infer the mass assembly history of galaxies by combining single stellar population (SSP) models that reproduce the observed spectrum. Using this methodology, we traced the star formation history of elliptical galaxies and, by studying the signatures left in the star formation history, we were able to constrain the feedback mechanisms regulating the star formation within halos. In the LCDM scenario, small scale structures are formed first, and then they merge forming larger and larger structures. Therefore, galaxies grow into more and more massive systems, and processes operating in these high-density environments change their properties. For this reason, galaxy evolution and formation of large-scale structures go hand in hand, as we show in our study of properties of galaxies in groups. We explored the spatial distribution of galaxies within and in the surrounding of groups, and we also used the velocity distribution of galaxies as a probe of the evolutionary stage of the group. We found important correlations between the evolutionary stage of the group and the population of galaxies residing within it.

Nos encontramos em uma localização vantajosa para o estudo da formação e evolução de galáxias espirais. Situados no disco da Via-Láctea, somos capazes de fazer observações detalhadas sobre as estrelas individuais que a compõem. Com o avanço tecnológico das últimas décadas, foi possível coletar um grande conjunto de informações, (e.g. composição química, cinemática, astrometria e parâmetros atmosféricos), com alta resolução para uma vasta parte do volume Galáctico. Com o objetivo de compreender melhor a nossa Galáxia, desenvolvemos uma ferramenta, chamada StarHorse, que estima parâmetros como distâncias, idades, massas e avermelhamento utilizando informação disponível em levantamentos espectroscópicos, fotométricos e astrométricos. O código StarHorse estima os parâmetros através de um método Bayesiano, que constrói uma distribuição de probabilidade a partir do cálculo de verossimilhança entre observações e modelos de evolução teórica e a partir de priores Galácticos bem conhecidos. Os parâmetros que o StarHorse estima são cruciais para estudos de arqueologia Galáctica. Com eles é possível investigar a estrutura, o histórico de formação estelar, a função de massa inicial, o mapa tridimensional da nossa Galáxia e também adicionar vínculos a modelos quemodinâmicos da Via Láctea Neste trabalho, focaremos na descrição e validação do método, testando sua aplicabilidade em levantamentos recentes de espectroscópica, astrometria e fotometria. Também disponibilizamos catálogos com distâncias e extinção para comunidade astronômica. As nossas distâncias e extinções se tornaram referência dentro da colaboração APOGEE e foram liberadas junto com o seu Data Release 14. Ademais, catálogos foram liberados para os surveys RAVE, Gaia-ESO e GALAH. Neste trabalho, exploramos os resultados do StarHorse, especialmente os resultados APOGEE, em um contexto amplo de arqueologia Galáctica. / We are in an advantageous position to study the formation and evolution of disk galaxies. By being inside the Milky Way, we are able to make detailed observations about the individual stars that compose it. With the technological revolution of the latest years, it has been possible to collect a massive set of information, (e.g. chemical composition, kinematics, astrometry, and atmospheric parameters), with high resolution for a large portion of the Galactic volume. With the goal to understand better our Galaxy, we developed a tool, called StarHorse, that can estimate distances, ages, masses, and extinction from the available spectroscopic, astrometric, and photometric information. StarHorse makes these estimates through a Bayesian method, that builds a probability distribution over the models by calculating a likelihood function between observation and stellar evolution models, and by using common knowledge about our Galaxy as priors. The parameters that StarHorse estimates are crucial to Galactic archaeology studies. With them, we can investigate the structure, the star formation history, the initial mass function, the three-dimensional dust map of our Galaxy, and provide constraints to chemodynamical models of the Milky Way. In this work, we focus on the description and validation of the method, testing its applicability in recent spectroscopic and astrometric surveys. We also make available catalogs with distances and extinctions to the astronomy community. Our distances and extinctions became a reference inside the APOGEE-team and were released as part of the SDSS Data Release 14. Moreover, we made available catalogs also to other spectroscopic surveys such as Gaia-ESO, RAVE, and GALAH. In this work, we also explore these results, especially for APOGEE, in a broad Galactic archaeology context.