Stellar population synthesis is a tool for modelling galaxies and their spectral energy distributions. By combining the spectra of every star within a galaxy, it becomes possible to form the spectrum of the galaxy as a whole. This requires a large collection of stellar spectra which, ideally, contains spectra for every kind of star in the model galaxy. To contribute to the development of stellar population synthesis and model atmospheres, I examine two such collections of stars, the MARCS and ATLAS9 theoretical stellar libraries. I compare 18 spectra of model stars for which both libraries have performed calculations. Stars with three different temperatures were chosen (8000K, 4500K and 3500K). For each temperature, three values of metallicity and two values of effective gravity were chosen. I find a mismatch in the spectra of the medium and low temperature model stars (4500K and 3500K), in addition, a difference in molecular features (~7000Å) is found in the 3500K low metallicity models ([Me/H]=-2.5). I conclude that this difference is caused by missing molecular opacities for the calcium hydride (CaH) molecule in the ATLAS9 library. Four possible causes of the overall mismatch are discussed: the temperature structure of the models; the geometry of the models; and partition functions used for the calculation of the models. I conclude that none of these four sources could produce the mismatch. This leaves room for further investigation into the cause of the mismatch.

abstract: The growing use of synthetic population, which is a disaggregate representation of the population of an area similar to the real population currently or in the future, has motivated the analysis of its sensitivity in the population generation procedure. New methods in PopGen have enhanced the generation of synthetic populations whereby both household-level and person-level characteristics of interest can be matched in a computationally efficient manner. In the process of set up, population synthesis procedures need sample records for households and persons to match the marginal totals with a specific set of control variables for both the household and person levels, or only the household level, for a specific geographic resolution. In this study, an approach has been taken to analyze the sensitivity by changing and varying this number of controls, with and without taking person controls. The implementation of alternative constraints has been applied on a sample of three hundred block groups in Maricopa County, Arizona. The two datasets that have been used in this study are Census 2000 and a combination of Census 2000 and ACS 2005-2009 dataset. The variation in results for two different rounding methods: arithmetic and bucket rounding have been examined. Finally, the combined sample prepared from the available Census 2000 and ACS 2005-2009 dataset was used to investigate how the results differ when flexibility for drawing households is greater. Study shows that fewer constraints both in household and person levels match the aggregate total population more accurately but could not match distributions of individual attributes. A greater number of attributes both in household and person levels need to be controlled. Where number of controls is higher, using bucket rounding improves the accuracy of the results in both aggregate and disaggregates level. Using combined sample gives the software more flexibility as well as a rich seed matrix to draw households which generates more accurate synthetic population. Therefore, combined sample is another potential option to improve the accuracy in matching both aggregate and disaggregate level household and person distributions. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2012

This thesis explores the evolution of galaxies from the onset of star formation shortly after the Big Bang until the present day. Particular emphasis lies on the redshift range z = 1.4 2.5, the so-called “redshift desert”, as it coincides with the peak epoch of cosmic star formation activity and mass assembly. Most of the information about galaxies and their evolution arrives in the form of their integrated light, i.e. the conglomeration of light emitted by stars of various ages and metallicities. In order to interpret the observed spectra and magnitudes, and to extract the physical parameters we therefore require models. This holds true in particular for galaxies too faint to target them spectroscopically, and for which redshifts and physical parameters derived from only their photometry is the only feasible way to study them in more detail. This thesis is concerned with such models, and describes how GALEV evolutionary synthesis models describe the spectral and chemical evolution of galaxies, accounting for gaseous emission and the increasing initial abundances of successive stellar generations, how they compare to observations and what we can learn from their application. Based on a large model grid, covering all observed galaxy evolution stages, I find that sub-solar metallicities have significant impact on the spectra of galaxies, and can lead to systematic errors and biases if not accounted for. A comparison of models with different metallicities furthermore reveals that photometric redshifts are also systematically biased if sub-solar metallicities are not properly accounted for. I also note that even a small mass-fractions of young stars can dominate the overall spectrum, leading to a large underestimation of the mass and age of the stellar population. The models explain not only the colour evolution of galaxies observed at a range of redshifts, but also their physical parameters. I show that with magnitudes in only a few bands we can successfully explain not only the masses of galaxies, but also their star formation rates and, where available from observations, their metallicities. If additional data are available, the grid of models can be used to refine colour selection criteria and to break degeneracies, e.g. between dust-reddened actively star-forming galaxies and intrinsically old, passively evolving galaxies. Using GAZELLE, a photometric redshift code that is purpose-tailored to harmonise with these models, I can extract accurate redshifts and a wealth of physical parameters from the largest ever sample of observed multi-wavelength photometry of galaxies. I then compare our findings with semi-analytical models that trace the evolution of individual galaxies based on cosmological simulations. In my sample I find a significant population of high-mass galaxies that is not accounted for by this class of models. Furthermore a small percentage of massive, yet starforming galaxies challenges our idea on how these galaxies form and evolve. In an appendix to this thesis I present a complementary approach to reconstruct the evolution of galaxies, using star clusters as tracers. I introduce a new technique to break the age-metallicity degeneracy and obtain individual ages and metallicities for a sample of globular clusters, revealing a merger of two Sb/Sc-type spirals 2 Gyrs ago in NGC 4570, a lenticular galaxy in the Virgo cluster. Also in the appendix I show that, at least in the studied galaxy Arp 78, the initial mass function conforms with our assumptions and does not change in low-density environments as recently predicted. Although studies of galaxy evolution are a major field in astronomy, there is still a lot more to be done to reveal the inner workings of these island universes, and this thesis also addresses how to continue and improve the work presented herein.

Population synthesis models (PSMs) are fundamental tools to study the star formation history and IMF of unresolved stellar populations using spectral features. This work presents a new set of PSMs constructed using theoretical isochrones and two state-ofthe- art synthetic spectral libraries. The BT-Settl and Munari libraries were chosen for their ability to predict the observed values of Lick-type and IMF-sensitive indices in individual stars of the solar neighbourhood. The BT-Settl library was used to sample the cool main sequence stars and the Munari library for the rest of the evolutionary phases. The PSMs cover a range of metallicities with [Fe/H]= 0, -1.31 and -1.81 for scaled-solar and α-enhanced metal mixtures. The models were used to study the behaviour of the IMF indices defined in the literature and the results are in good agreement with what other PSMs have determined. The PSMs in this work predict a strong degeneracy between age, metallicity and IMF. I used the models to study which are the main evolutionary phases contributing to each IMF-sensitive index and found that most indices reach their final integrated values before the turn off. The post-main sequence stars contribute mainly to the continuum of these bands. Uncertainties in the the effective temperature of the isochrones can affect IMF estimates. The PSMs were applied to extragalactic globular clusters (GCs) and early-type galaxies (ETGs) using data from the literature. I determined the ages, metallicities and IMFs of these systems using index combinations in the optical and infrared. I explored how the morphology of the Horizontal Branch (HB) and dynamical evolution (which are key uncertainties in the modelling of GCs) can affect the IMF predictions. In a population with a Milky Way IMF, dynamical evolution can make the IMF indices mimic a bottom-light IMF. HB morphology has no impact on the IMF estimates at low [Fe/H]. In the IMF index-index diagrams for GCs, the results are significantly affected by the unknown sodium abundances of these systems. Using the PSMs in this work the best index combination to determine the IMF is CaH1 and TiO2. The ETGs and the [Fe/H]=0 GCs appear to have a bottom-heavy IMF with x ~ 3:0. These results are discussed in the work.

Les coûts élevés de collecte de données ne rendent souvent possible que l’échantillonnage d’un sous-ensemble de la population d’intérêt. Il arrive également que les données collectées renferment des renseignements personnels et sensibles au sujet des individus qui y figurent de sorte qu’elles sont protégées par des lois ou des pratiques strictes de sécurité et gouvernance de données. Dans les deux cas, l’accès aux données est restreint. Nos travaux considèrent deux angles de recheche sous lesquels on peut se servir de la génération de données fictives pour concevoir des modèles d’analyse où les données véritables sont inaccessibles. Sous le premier angle, la génératon de données fictives se substitue aux données du recensement. Elle prend la forme d’une synthèse de population constituée d’individus décrits par leurs attributs aux niveaux individuel et du ménage. Nous proposons les copules comme nouvelle approche pour modéliser une population d’intérêt dont seules les distributions marginales sont connues lorsque nous possédons un échantillon d’une autre population qui partage des caractéristiques de dépendances interdimensionnelles similaires. Nous comparons les copules à l’ajustement proportionnel itératif, technologie répandue dans le domaine de la synthèse de population, mais aussi aux approches d’apprentissage automatique modernes comme les réseaux bayésiens, les auto-encodeurs variationnels et les réseaux antagonistes génératifs lorsque la tâche consiste à générer des populations du Maryland dont les données sont issues du recensement américain. Nos expériences montrent que les copules surpassent l’ajustement proportionnel itératif à modéliser les relations interdimensionnelles et que les distributions marginales des données qu’elles génèrent correspondent mieux à celles de la population d’intèrêt que celles des données générées par les méthodes d’apprentissage automatique. Le second angle considère la génération de données qui préservent la confidentialité. Comme la désensibilisation des données est en relation inverse avec son utilité, nous étudions en quelles mesures le k-anonymat et la modélisation générative fournissent des données utiles relativement aux données sensibles qu’elles remplacent. Nous constatons qu’il est effectivement possible d’employer ces définitions de confidentialité pour publier des données utiles, mais la question de comparer leurs garanties de confidentialité demeure ouverte. / The high costs of data collection can restrict sampling so that only a subset of the data is available. The data collected may also contain personal and sensitive information such that it is protected by laws or strict data security and governance practices. In both cases, access to the data is restricted. Our work considers two research angles under which one can use the generation of synthetic data to design analysis models where the real data is inaccessible. In the first project, a synthetically generated population made up of individuals described by their attributes at the individual and household levels replaces census data. We propose copulas as a new approach to model a population of interest whose only marginal distributions are known when we have a sample from another population that shares similar interdimensional dependencies. We compare copulas to iterative proportional fitting, a technology developed in the field of population synthesis, but also to modern machine learning approaches such as Bayesian networks, variational autoencoders, and generative adversarial networks when the task is to generate populations of Maryland. Our experiments demonstrated that the copulas outperform iterative proportional fitting in modeling interdimensional relationships and that the marginal distributions of the data they generated match those of the population of interest better than those of the data generated by the machine learning methods. The second project consists of generating data that preserves privacy. As data privacy is inversely related to its usefulness, we study to what extent k-anonymity and generative modeling provide useful data relative to the sensitive data they replace. We find that it is indeed possible to use these privacy definitions to publish useful data, but the question of comparing their privacy guarantees remains open.

L’étude des amas globulaires (AGs) nous offre une opportunité d’appréhender l’histoire de leurs galaxies hôtes et ainsi l’histoire de l’univers. Dans cette thèse, je me suis intéressé aux propriétés des AGs dans différents environnements. Tout d’abord, je me suis concentré sur les AGs de l’amas de la Vierge, un amas de galaxies très dense situé à environ 16,5 Mpc. J’ai utilisé les données observées par le relevé NGVS (Next Generation Virgo Survey) pour définir un échantillon qui contient 1846AGs. J’ai ensuite comparé les couleurs de ces amas avec celles d’autres AGs originaires de la Voie Lactée et j’ai remarqué des différences de couleurs encore jamais observées, dont la nature exacte est encore énigmatique. Pour comprendre ces différences, j’ai ensuite comparé les AGs observés avec des AGs synthétiques basés sur 10 modèles de synthèse de populations stellaires. J’ai aussi étudié les âges et les métallicités ressortant de la confrontation directe des couleurs des AGs à ces modèles. En conclusion, en l’état actuel, les modèles ne rendent pas compte de la diversité identifiée dans ma thèse. Finalement, j’ai effectué une brève étude des propriétés spatiales des AGs autour de M87 pour repérer des marques d’accrétion. / Through the study of the globular cluster (GC) properties, it is possible to unravel the history of their host galaxies and by extension the history of the universe. During this thesis, I was interested in the GC properties in different environments. First, I looked at the GCs in the Virgo cluster, a dense galaxy cluster located at 16.5 Mpc. I used data from the survey NGVS (Next Generation Virgo Survey) to define a sample of 1846 GCs. Then, I compared the colors of these GCs with those of Milky Way GCs and I noted color differences never yet observed, which are still enigmatic. In order to understand these differences, I compared the observed GCs with synthetic GCs obtained with 10 stellar population synthesis models. I also studied the age and metallicity predictions of those models. In the end, in their current status, the models do not account for the diversity highlighted in my thesis. Finally, I assessed the spatial properties of the GCs around M87 in order to find any signatures of a recent accretion.

Je présente ma thèse sur l'analyse des ondes gravitationnelles dans les deux domaines suivants. Pour le premier il s'agit de vérifier que les collaborations LIGO et Virgo sont prêtes pour la détection d'un fond gravitationnel stochastique astrophysique pendant l'ère des détecteurs avancés qui va démarrer à l'été 2015. Pour le deuxième il s'agit de poursuivre l'étude du potentiel scientifique, notamment pour l'astrophysique et la cosmologie, d'un détecteur de troisième génération, le Einstein Telescope. Dans les deux cas, j'utilise des "mock data and science challenges" qui consistent à simuler Les données des détecteurs gravitationnels contenant un grand nombre de sources distribuées de façon réalistes dans l'espace des paramètres. / Here I present my thesis investigating gravitational-wave data analysis in the following two areas. The first is to test the readiness of the LIGO-Virgo collaborations to the advanced detector era, which will begin in the summer of 2015, to make a detection of an astrophysical stochastic gravitational-wave background. The second is to continue an investigation into the science potential of a conceived, third generation gravitational-wave detector, the Einstein Telescope, in terms of astrophysics and cosmology. Both of these are conducted with the use of mock data and science challenges which consists of the production of expected gravitational-wave detector data, containing a large number of sources, that are simulated using realists distributions.

The main objective of the thesis is to study the properties of the Galactic population of radio-quiet and thermally emitting isolated neutron stars (INSs). This is done by studying further the existing neutron star sample of nearby seven sources, known as the Magnificent Seven (M7), as well as by searching for new candidates and constraining possible populations. During the thesis, we investigated the proper motions of three of the faintest M7 in X-rays with the satellite Chandra. This work allowed us to constrain the neutron star displacement in two cases as well as to accurately determine the high proper motion of a third source, for the first time in X-rays with a significance approaching 10 standard deviations (Motch, Pires, Haberl, & Schwope, 2007, Ap&SS, 308, 217; Motch, Pires, Haberl, Schwope, & Zavlin, 2009, A&A 497, 423). The search of new INS candidates in the serendipitous catalogue of the XMM-Newton Observatory, with more than 120,000 X-ray sources, had as well the aim to constrain the spatial density of thermally emitting sources located beyond the solar vicinity. This work allowed the long awaited discovery of a new thermally emitting INS with properties similar to those of the seven nearby sources discovered by ROSAT (Pires, Motch, Turolla, Treves, & Popov, 2009, A&A 498, 233). Moreover, deep optical observations with SOAR and the ESO-VLT have been obtained during the thesis work in order to optically identify a handful of INS candidates that have been selected among more than 72,000 sources (Pires, Motch, & Janot-Pacheco, 2009, A&A, 504, 185). Finally, population synthesis of Galactic thermally emitting INSs allows constraining the global properties of this population based on the whole sample of XMM-Newton observations. By estimating the density of similar sources at more remote distances in the Milky Way, the final objective is to determine whether the spatial density derived from the group of seven nearby sources is a local anomaly caused by the Suns current location near regions of active stellar formation of the Gould Belt. / O objetivo da tese é estudar as propriedades da população Galáctica de estrelas de nêutrons isoladas com emissão térmica em raios X mas silenciosas em rádio. Isto é feito iinvestigando-se a amostra existente de sete fontes próximas, conhecidas como Magnificent Seven (M7), assim como através da procura por novos candidatos e restringindo possíveis cenários e populações. Durante a tese, nós investigamos os movimentos próprios de três das mais fracas fontes em raios X com o satélite Chandra. Este trabalho nos permitiu restringir o deslocamento da estrela de nêutrons em dois casos assim como medir com grande precisão o alto valor de movimento próprio de uma terceira fonte, pela primeira vez em raios X com uma precisão alcançando 10 desvios-padrão (Motch, Pires, Haberl & Schwope, 2007, Ap&SS, 308, 217; Motch, Pires, Haberl, Schwope & Zavlin, 2009, A&A 497, 423). A procura por novos candidatos a estrelas de nêutrons isoladas no catálogo de fontes do satélite XMM-Newton, com mais de 120.000 fontes de raios X, teve igualmente como objetivo restringir a densidade espacial de fontes com emissão térmica situadas além da vizinhança solar. Este trabalho levou à aguardada descoberta de uma nova estrela de nêutrons isolada em processo de resfriamento, a qual exibe propriedades similares às sete fontes descobertas pelo ROSAT (Pires, Motch, Turolla, Treves, & Popov, 2009, A&A 498, 233). Mais ainda, observações óticas profundas com os telescópios SOAR e ESO-VLT foram obtidas durante a tese de maneira a identificar no óptico a amostra mais brilhante de candidatos a estrelas de nêutrons, os quais foram selecionados entre mais de 72.000 fontes (Pires, Motch, & Janot-Pacheco, 2009, A&A, 504, 185). Finalmente, a síntese de população de estrelas de nêutrons isoladas Galácticas permite restringir as propriedades globais da população com base na amostra total de observações em raios X realizadas com o satélite XMM-Newton. Estimando-se a densidade de fontes similares a maiores distâncias na Via Láctea, o objetivo final é determinar se a densidade espacial derivada do grupo de sete estrelas próximas corresponde a uma anomalia local causada pela proximidade do Sol em relação a regiões de ativa formação estelar do Cinturão de Gould.

Supermassive black holes, black holes with masses <106 Msun, are found at the centers of all massive galaxies. These massive black holes grew from smaller seed black holes through accretion events. Accreting black holes are very bright in the radio through very hard X-ray spectral regimes. Due to the location of these accreting black holes at the centers of galaxies, they are referred to as active galactic nuclei (AGN). It is understood that AGN are an important phase of galaxy evolution; however, the role of AGN in massive galaxy formation is very poorly constrained. Here, the unique tool of multi-wavelength population synthesis modeling is used to study the average properties of AGN and their host galaxies with a focus on host galaxy star formation and the role of black hole growth in galaxy evolution. Knowledge of the AGN population from deep X-ray surveys is combined with theoretical AGN spectral energy distributions to predict various observables of the AGN population in wavelength regions from the far infrared to very hard X-rays. Comparison of the model predictions to observations constrains the model input parameters and allows for the determination of average properties of the AGN population. Particular attention is paid to a special class of AGN known as Compton thick AGN. These AGN are deeply embedded in gas and dust such that the column density obscuring the line of sight to the central engine of the AGN exceeds 1/σT ~ 10²⁴ cm⁻², where σT is the Thomson cross-section of the electron---a column density comparable to that of the human chest. Theoretical and simulational evidence suggest that these Compton thick AGN may be recently triggered, rapidly accreting AGN, making them of special interest to researchers. I found that Compton thick AGN are likely to contribute ~20% of the peak of the cosmic X-ray background (XRB) at ~30 keV and demonstrated that a significant portion of Compton thick AGN may be accreting very rapidly. Moreover, Compton thick AGN do not appear to follow the orientation based unified model of AGN. According to the unified model, AGN exhibit a range of obscuration levels due to a dusty 'torus' which, depending on the orientation of the torus to the observer's line of sight, may obscure the central engine of the AGN. Upon further investigation into the stellar populations of AGN host galaxies, it appears that the unified model holds in general at z < 1, but not at z > 1. I found that this is likely due to the dominant triggering mechanism of AGN switching from major mergers at z > 1.5 to secular processes by z ~ 1.

The main objective of the thesis is to study the properties of the Galactic population of radio-quiet and thermally emitting isolated neutron stars (INSs). This is done by studying further the existing neutron star sample of nearby seven sources, known as the Magnificent Seven (M7), as well as by searching for new candidates and constraining possible populations. During the thesis, we investigated the proper motions of three of the faintest M7 in X-rays with the satellite Chandra. This work allowed us to constrain the neutron star displacement in two cases as well as to accurately determine the high proper motion of a third source, for the first time in X-rays with a significance approaching 10 standard deviations (Motch, Pires, Haberl, & Schwope, 2007, Ap&SS, 308, 217; Motch, Pires, Haberl, Schwope, & Zavlin, 2009, A&A 497, 423). The search of new INS candidates in the serendipitous catalogue of the XMM-Newton Observatory, with more than 120,000 X-ray sources, had as well the aim to constrain the spatial density of thermally emitting sources located beyond the solar vicinity. This work allowed the long awaited discovery of a new thermally emitting INS with properties similar to those of the seven nearby sources discovered by ROSAT (Pires, Motch, Turolla, Treves, & Popov, 2009, A&A 498, 233). Moreover, deep optical observations with SOAR and the ESO-VLT have been obtained during the thesis work in order to optically identify a handful of INS candidates that have been selected among more than 72,000 sources (Pires, Motch, & Janot-Pacheco, 2009, A&A, 504, 185). Finally, population synthesis of Galactic thermally emitting INSs allows constraining the global properties of this population based on the whole sample of XMM-Newton observations. By estimating the density of similar sources at more remote distances in the Milky Way, the final objective is to determine whether the spatial density derived from the group of seven nearby sources is a local anomaly caused by the Suns current location near regions of active stellar formation of the Gould Belt. / O objetivo da tese é estudar as propriedades da população Galáctica de estrelas de nêutrons isoladas com emissão térmica em raios X mas silenciosas em rádio. Isto é feito iinvestigando-se a amostra existente de sete fontes próximas, conhecidas como Magnificent Seven (M7), assim como através da procura por novos candidatos e restringindo possíveis cenários e populações. Durante a tese, nós investigamos os movimentos próprios de três das mais fracas fontes em raios X com o satélite Chandra. Este trabalho nos permitiu restringir o deslocamento da estrela de nêutrons em dois casos assim como medir com grande precisão o alto valor de movimento próprio de uma terceira fonte, pela primeira vez em raios X com uma precisão alcançando 10 desvios-padrão (Motch, Pires, Haberl & Schwope, 2007, Ap&SS, 308, 217; Motch, Pires, Haberl, Schwope & Zavlin, 2009, A&A 497, 423). A procura por novos candidatos a estrelas de nêutrons isoladas no catálogo de fontes do satélite XMM-Newton, com mais de 120.000 fontes de raios X, teve igualmente como objetivo restringir a densidade espacial de fontes com emissão térmica situadas além da vizinhança solar. Este trabalho levou à aguardada descoberta de uma nova estrela de nêutrons isolada em processo de resfriamento, a qual exibe propriedades similares às sete fontes descobertas pelo ROSAT (Pires, Motch, Turolla, Treves, & Popov, 2009, A&A 498, 233). Mais ainda, observações óticas profundas com os telescópios SOAR e ESO-VLT foram obtidas durante a tese de maneira a identificar no óptico a amostra mais brilhante de candidatos a estrelas de nêutrons, os quais foram selecionados entre mais de 72.000 fontes (Pires, Motch, & Janot-Pacheco, 2009, A&A, 504, 185). Finalmente, a síntese de população de estrelas de nêutrons isoladas Galácticas permite restringir as propriedades globais da população com base na amostra total de observações em raios X realizadas com o satélite XMM-Newton. Estimando-se a densidade de fontes similares a maiores distâncias na Via Láctea, o objetivo final é determinar se a densidade espacial derivada do grupo de sete estrelas próximas corresponde a uma anomalia local causada pela proximidade do Sol em relação a regiões de ativa formação estelar do Cinturão de Gould.