Polarised synchrotron emission from the Milky Way is of interest for its role as a foreground to the polarised CMB and as a probe of the interstellar medium. The Galactic ALFA Continuum Transit Survey (GALFACTS) and the Global Magneto-Ionic Medium Survey (GMIMS) are two ongoing surveys of the diffuse polarised emission around 1.4 GHz, with wide bandwidths and high frequency-resolution. In this thesis, I use early data from GALFACTS to investigate the behaviour of polarised, diffuse Galactic synchrotron emission. I also analyse GMIMS total intensity data. I derive a rotation measure (RM) map of the GALFACTS sky using a combination of RM-synthesis and linear angle fitting, commenting on the structure of the maps in general and on specific regions in particular. Overall I find that the maps are rich in features, and probe the RM structure of the extended Galactic emission with reasonable accuracy. I also derive the Angular Power Spectrum (APS) of the polarised emission for thirty-one 15 by 15 degree subregions across the GALFACTS data. I compute the E- and B-modes (E+B) and the scalar APS of the polarised emission (PI). I parametrise the APS by fitting a power law to the data. Comparing the E+B APS to the PI APS shows that E+B is consistently steeper across the sky. The APS data is also used to estimate the level of foreground contamination of the CMB B-mode by the synchrotron emission. I find that the slope of the APS averaged over high-latitude, low-emission subregions agrees exactly with that of the Planck 30 GHz polarised emission, thus setting an upper limit to the synchrotron contamination of CMB B-modes. Finally, I evaluate the spurious, systematic, temperature zero-level offset and associated uncertainty in preliminary GMIMS total intensity maps, finding a lower limit of ±0.26 K. I also make spectral index maps made using the GMIMS data and the Haslam et al. (1982) 408 MHz map, improving upon previous spectral index maps in the literature.

Le milieu interstellaire (MIS) où se forment les étoiles est constitué de gaz très dilué dominé par l'hydrogène moléculaire, et de grains de poussière de taille submicrométrique. Ces poussières jouent un rôle crucial en atténuant la lumière des étoiles lointaines, protégeant ainsi les molécules du gaz des rayonnements ultra-violets, et en servant de catalyseurs à une chimie hétérogène à très basse température. Outre la synthèse de l'hydrogène moléculaire, la surface des grains permet de former des molécules organiques dites complexes comme le méthanol (CH3OH) à partir de l'hydrogénation (et la deutération) du monoxyde de carbone (CO). Les glaces ainsi formées participent à la complexification moléculaire du MIS et seront à terme intégrées au sein de disques de poussières, berceaux des astéroïdes, comètes et exo-planètes. L'objectif de cette thèse est l'étude des mécanismes d'échanges hydrogène-deuterium sur certains groupements fonctionnels de molécules organiques simples, méthanol par exemple, présentes à la surface ou dans les manteaux des grains interstellaires. La thèse est centrée sur une exploration expérimentale de ces processus en phase condensée, à l'aide d'une expérience de cryogénie synthétisant des glaces à très basse température (15K) couplée à un spectromètre infrarouge. Nous montrons que ces échanges se produisent avant la sublimation du manteau de glace sur des groupes fonctionnels capables d'établir des liaisons hydrogènes avec les molécules d'eau voisines. Le processus catalysant est vraisemblablement la cristallisation de la glace d'eau. Des études cinétiques nous permettent d'évaluer les énergies d'activation du transfert H/D (6745K) et de la transition amorphe-cristalline (8100K), et de déterminer la constante de vitesse d'échange dans le domaine de température 120-140~K. Cette constante de vitesse est, de plus, comparée à des calculs semi-classiques basés sur un traitement ab initio. En marge de ces expériences, des observations millimétriques de la molécule de méthanol en direction de proto-étoiles confirment une variabilité des abondances relatives des isotopologues simplement deutérés de cette molécule en fonction de la masse de la protoétoile. / The interstellar medium where stars are formed consists of a dilute gas which is dominated by molecular hydrogen and dust grains less than a few microm in size. The dust plays a crucial role in the attenuation of light from the stars. They also protect molecules within the gas from UV photons. Furthermore, they serve as heterogeneous catalysts for chemistry at low temperature. The surface of the grains also permit the formation of complex organic molecules such as methanol via the hydrogenation and/or deuteration of carbon monoxide. The ices are formed and subsequently participate in increasing the molecular complexity of the clouds. Finally, they are incorporated into debris disks, asteroids, comets, and exoplanets. The objective of this thesis is to study the mechanism of hydrogen/deuterium exchange within certain functionnal groups of simple organic molecules such as methanol, which are present on the surface of these grain mantles. The thesis is focused on the experimental determination of these processes in the condensed phase. This will be achieved with the aid of a cryogenic synthesis of the ices at very low temperatures coupled with infrared spectrometry. We observe that it is possible for the exchange to proceed before the sublimation of the ice mantles. However, this is only the case when the functional groups within the molecule may form hydrogen bonds with water. From our results we see that this process seems to be catalysed by the crystalization of the water ice. The kinetics study permits us to evalute the activation energy for the H/D exchange (6745 K) and for the transition from amorphous to crystaline ice (8100 K). In addition it also allows us to determine the rate constant for the exchange in the temperature range 120-140 K. In addition we have performed theoretical calulation in an attempt to elucidate the mechanism for the exchange. However, the experimental rate constant for the exchange is much larger in comparison to the one predicted by a semi- classical treatment based on the AB initio potential we have obtained. Further to this observations of methanol towards protostars have been conducted. These observations show that there is a variation in the relative abundance of the CH2DOH and CH3OD. This variation in relative abundance seems to have some dependence upon the mass of the protostar, with high mass stars showing (CH2DOH/CH3OD ≤ 1) and low/intermiediate mass stars showing (CH2DOH/CH3OD >> 3).

Os cianopoliinos (HCnN, n = 1, 3, 5, ...) e seus isômeros, os isocianopoliinos (HCn-1NC), constituem duas famílias de moléculas já identificadas no meio interestelar. No intuito de auxiliar a detecção e investigar a formação destas moléculas neste ambiente, foram obtidas as geometrias, as constantes rotacionais, os momentos de dipolo, as frequências vibracionais e as intensidades fundamentais de infravermelho em níveis MP2/cc-pVTZ (n = 1 a 17), CCSD/cc-pVDZ (n = 1 a 13) e CCSD/cc-pVTZ (n = 1 a 7). Além disso, foi empregado o modelo de partição em carga - fluxo de carga - fluxo de dipolo, CFCFD, em termos dos multipolos atômicos advindos da Teoria Quântica de Átomos em Moléculas, QTAIM, para compreender os efeitos do tamanho da cadeia sobre as propriedades elétricas destas moléculas, como suas intensidades de infravermelho. Os resultados indicam que o nível CCSD/cc-pVTZ é o que melhor descreve as propriedades mencionadas para os menores cianopoliinos e isocianopoliinos. Contudo, devido à demanda computacional, é preciso optar entre os níveis MP2/cc-pVTZ e CCSD/cc-pVDZ para abordar espécies maiores. Assim, os momentos de dipolo destes maiores cianopoliinos são mais bem descritos pelo nível MP2/cc-pVTZ, enquanto CCSD/cc-pVDZ é mais indicado para tal propriedade em respectivos isocianopoliinos. Por sua vez, as intensidades de infravermelho destas famílias apresentam melhor concordância com dados experimentais quando determinadas em nível CCSD/cc-pVDZ. Além disso, tanto para cianopoliinos quanto para isocianopoliinos, o aumento do tamanho das cadeias resulta num incremento das intensidades do estiramento CH, o que é explicado por variações no fluxo de carga eletrônica. O estiramento das ligações triplas CC centrais é o modo mais intenso em grandes cianopoliinos, o que também se deve ao fluxo de carga observado. Ademais, o espectro dos isocianopoliinos apresenta um número maior de bandas relevantes na região de estiramento de ligações triplas CC. Um estudo também foi conduzido, onde foram estimados os dados termodinâmicos, as geometrias do estado de transição e as constantes de velocidade da reação HCnN → HCn-1NC (n = 1 a 9) para temperaturas entre 298,15 e 3000 K. Os níveis B3LYP/aug-cc-pVsZ, MPW1K/aug-cc-pVsZ (s = Q) e CCSD(T)/aug-cc-pVmZ (m = T e Q) foram adotados em um tratamento composto para as reações com n = 1, 3 e 5, enquanto as reações com n = 7 e 9 foram investigadas de forma semelhante, porém com s = T e m = D e T. O método B3LYP foi o que apresentou melhor desempenho comparado ao MPW1K na determinação de frequências e geometrias. Os resultados indicam que esta reação é exotérmica no sentido em que os cianopoliinos são formados e, portanto, é mais fácil de ocorrer em ambientes mais frios do meio interestelar. Por outro lado, suas constantes de velocidade no sentido direto e inverso tendem a ser de mesma magnitude em temperaturas elevadas, indicando que estes ambientes mais quentes são mais propícios para detecção de isocianopoliinos. Por fim, equações parametrizadas foram ajustadas para reproduzir nossos dados de constantes de velocidade das reações com n = 1 até 9 dentro do intervalo de temperaturas considerado. / Cyanopolyynes (HCnN, n = 1, 3, 5, ...) and their isomers, isocyanopolyynes (HCn-1NC), constitute two families of molecules already identified in the interstellar medium. In order to provide data for their detection and to investigate the formation of these molecules in this environment, geometries, rotational constants, dipole moments, vibrational frequencies and infrared fundamental intensities were obtained at MP2/cc-pVTZ (n = 1 to 17), CCSD/cc-pVDZ (n = 1 to 13) and CCSD/cc-pVTZ (n = 1 to 7) levels. Furthermore, the partition model in charge - charge flux - dipole flux, CFCFD, from atomic multipoles given by the Quantum Theory of Atoms in Molecules, QTAIM, was applied to understand the effects of chain size on electrical properties of these molecules, such as intensities. Results indicate that the best description of the properties mentioned is achieved at the CCSD/cc-pVTZ level for smaller cyanopolyynes and isocyanopolyynes. However, due to computational demand, one needs to choose between MP2/cc-pVTZ and CCSD/cc-pVDZ levels to deal with larger species. In this sense, the dipole moments of large cyanopolyynes are better described by the MP2/cc-pVTZ level, while CCSD/cc-pVDZ is indicated for such property in respective isocyanopolyynes. In addition, the infrared intensities of both families from CCSD/cc-pVDZ calculations are in better accordance with experimental data. Moreover, chain size increases of cyanopolyynes and isocyanopolyynes result in intensity increments of CH stretching, which is explained by electronic charge flux changes. The stretching of central CC triple bonds is the strongest mode for large cyanopolyynes and this is also due to charge flux. A study was also conducted, in which thermodynamic data, transition state geometries and rate constants of the reaction HCnN → HCn-1NC (n = 1 to 9) were estimated for temperatures between 298.15 and 3000 K. B3LYP/aug-cc-pVsZ, MPW1K/aug-cc-pVsZ (s = Q) and CCSD(T)/aug-cc-pVmZ (m = T and Q) were adopted in a combined treatment for reactions with n = 1, 3 and 5, while reactions with n = 7 and 9 were investigated in a similar way, but with s = T and m = D and T. Frequencies and geometry data from the B3LYP method exhibited a better performance than MPW1K. The results indicated that this reaction is exothermic in the direction that leads to cyanopolyynes, and therefore it is easier to occur in colder environments of the interstellar medium. On the other hand, rate constants of forward and reverse reactions tend to show the same magnitude at higher temperatures, indicating these warmer environments are more amenable to detection of isocyanopolyynes. Finally, parameterized equations were fitted to reproduce our rate constant data for reactions with n = 1 to 9 in the temperature range considered.

Les étoiles massives, de type O ou B, sont d'une importance capitale pour le budget énergétique des galaxies et l'enrichissement du milieu interstellaire. Néanmoins, leur formation, contrairement à celle des étoiles de type solaire reste sujet à débats, sinon une énigme. Les toutes premières étapes de la formation des étoiles massives ainsi que la formation de leur nuage parent sont des thèmes qui stimulent une grande activité sur les plans théorique et observationnel depuis une décennie. Il semble maintenant acquis que les étoiles massives naissent dans des cœurs denses massifs, qui se forment au travers de processus dynamiques, tels que les flots de gaz collisionnels. Au cours de ma thèse, j'ai mené une étude approfondie de la formation des cœurs denses et des étoiles massives au sein de la structure hypermassive W43-MM1, localisée à 6~kpc du soleil. Dans un premier temps, j'ai montré une corrélation directe entre l'efficacité à former des étoiles et la densité volumique des nuages moléculaires, en décalage avec un certain nombre d'études précédentes. En effet, la distribution spatiale et de masse des cœurs denses massifs en formation au sein de W43-MM1 suggère que ce filament hypermassif est en phase de flambée de formation d'étoiles, flambée d'autant plus grande que l'on se rapproche de son cœur. J'ai comparé ces résultats observationnels aux modèles numériques et analytiques d'efficacité de formation stellaire les plus récents. Cette confrontation permet non seulement d'apporter de nouvelles contraintes sur la formation des filaments hypermassifs, mais suggère aussi que la compréhension de la formation d'étoiles dans les nuages hypermassifs nécessite une description fine de la structure de ces objets exceptionnels. En second lieu, ayant montré que la formation des étoiles massives est fortement dépendante des propriétés des filaments qui les forment, je me suis naturellement intéressé aux processus de formation de ces filaments, grâce à une étude de leur dynamique globale. Plus précisément, j'ai utilisé un traceur de chocs (la molécule de SiO) pour discerner les chocs dûs aux processus locaux de formation des étoiles (jets et flots bipolaires), des chocs dûs aux processus permettant la formation du nuage. J'ai ainsi pu, via une étude sans précédent alliant observations et modélisation de chocs dans une région formant de nombreuses étoiles, montrer l'existence de chocs à basse vitesse, première signature directe de la formation du nuage moléculaire dans lequel les étoiles massives se forment. Ces résultats constituent une étape importante reliant, via des processus dynamiques, la formation des nuages moléculaires à la formation des étoiles massives. / O and B types stars are of paramount importance in the energy budget of galaxies and play a crucial role enriching the interstellar medium. However, their formation, unlike that of solar-type stars, is still subject to debate, if not an enigma. The earliest stages of massive star formation and the formation of their parent cloud are still crucial astrophysical questions that drew a lot of attention in the community, both from the theoretical and observational perspective, during the last decade. It has been proposed that massive stars are born in massive dense cores that form through very dynamic processes, such as converging flows of gas. During my PhD, I conducted a thorough study of the formation of dense cores and massive stars in the W43-MM1 supermassive structure, located at ~ 6 kpc from the sun. At first, I showed a direct correlation between the star formation efficiency and the volume gas density of molecular clouds, in contrast with scenarii suggested by previous studies. Indeed, the spatial distribution and mass function of the massive dense cores currently forming in W43-MM1 suggests that this supermassive filament is undergoing a star formation burst, increasing as one approaches its center. I compared these observational results with the most recent numerical and analytical models of star formation. This comparison not only provides new constraints on the formation of supermassive filaments, but also suggests that understanding star formation in high density, extreme ridges requires a detailed portrait of the structure of these exceptional objects. Second, having shown that the formation of massive stars depends strongly on the properties of the ridges where they form, I studied the formation processes of these filaments, thanks of the characterization of their global dynamics. Specifically, I used a tracer of shocks (SiO molecule) to disentangle the feedback of local star formation processes (bipolar jets and outflows) from shocks tracing the pristine formation processes of the W43-MM1 cloud. I was able, via an unprecedented study combining observations and modeling of shocks in a starbust region, to show the existence of widespread low velocity shocks, that are the first direct signature of the formation of the massive molecular cloud from which massive stars form.These results are an important step connecting, via dynamical processes, the formation of molecular clouds to the formation of massive stars.

Le milieu interstellaire (MIS) est un système extrêmement complexe. Il correspond à une échelle intermédiaire entre les étoiles et les galaxies. Le gaz interstellaire est présent dans toute la galaxie, remplissant l’espace entre les étoiles. Une grande diversité de processus couplés, comme la gravité, le champs magnétiques, la turbulence et la chimie, participe à son évolution, faisant de la modélisation du MIS un problème ardu. Une description correcte du MIS nécessite un bon traitement des équations de la magnetohydrodynamique (MHD), de la gravité, du bilan thermique et de l’évolution chimique à l’intérieur du nuage moléculaire.L’objectif de ce travail de thèse est une meilleure compréhension de la formation et de l’évolution des nuages moléculaires, et plus particulièrement de la transition du gaz atomique en gaz moléculaire. Nous avons réalisé des simulations numériques de la formation des nuages moléculaires et de la formation de l’hydrogène moléculaire sous l’influence de la gravité et de la turbulence MHD, en utilisant des estimations précises de l’écrantage par les poussières et de l’auto-écrantage par la molécule H2. Ceci a été calculé grâce à une méthode en arbre, à même de fournir une rapide estimation des densités de colonne.Nous avons trouvé que l’hydrogène moléculaire se forme plus rapidement que prévu par les estimations classiques du fait de l’augmentation de densité locale provoquée par les fluctuations turbulentes du gaz. L’hydrogène moléculaire, formé à des densités plus élevées, peut alors migrer vers les régions plus chaudes et moins denses.Les densités de colonne totale d’hydrogène moléculaire montrent que la transition HI-H2 se produit à des densités de colonne de quelques 10^20 cm−2. Nous avons calculé les populations des niveaux rotationnels de H2 à l’équilibre thermique et intégré le long de plusieurs lignes de visée. Ces résultats reproduisent bien les valeurs observées par Copernicus et FUSE, suggérant que la transition observée et les populations excitées pourraient être une conséquence de la structure multi-phasique des nuages moléculaires. Comme la formation de H2 précède la formation des autres molécules, le H2 chaud pourrait permettre le développement d’espèces endothermiques et éventuellement expliquer certains aspects de la richesse moléculaire observée dans l’ISM. / The interstellar medium (ISM) is a highly complex system. It corresponds to an intermediate scale between stars and galaxies. The interstellar gas is present throughout the galaxy, filling the volume between stars. A wide variety of coupled processes, such as gravity, magnetic fields, turbulence and chemistry, participate in its evolution, making the modeling of the ISM a challenging problem. A correct description of the ISM requires a good treatment of the magnetohydrodynamics (MHD) equations, gravity, thermal balance, and chemical evolution within the molecular clouds.This thesis work aims at a better understanding of the formation and evolution of molecular clouds, specially how they become "molecular", paying particular attention to the transition HI-to-H2. We have performed ideal MHD simulations of the formation of molecular clouds and the formation of molecular hydrogen under the influence of gravity and turbulence, using accurate estimates for the shielding effects from dust and the self-shielding for H2, calculated with a Tree-based method, able to provide fast estimates of column densities.We find that H2 is formed faster than predicted by the usual estimates due to local density enhancements created by the gas turbulent motions. Molecular hydrogen, formed at higher densities, could then migrate toward low density warmer regions.Total H2 column densities show that the HI-to-H2 transition occurs at total column densities of a few 10^20 cm−2. We have calculated the populations of rotational levels of H2 at thermal equilibrium, and integrated along several lines of sight. These two results reproduce quite well the values observed by Copernicus and FUSE, suggesting that the observed transition and the excited populations could arise as a consequence of the multi-phase structure of molecular clouds. As H2 formation is prior to further molecule formation, warm H2 could possibly allow the development of a warm chemistry, and eventually explain some aspects of the molecular richness observed in the ISM.

Je combine de nouveaux modèles de production de radiations stellaires et de transport radiatif à travers le milieu interstellaire (MI). Cela permet de caractériser les étoiles ainsi que le MI neutre et ionisé dans des galaxies formant des étoiles (GFE), via des raies ultraviolettes dans leur spectre. J'évalue la fiabilité des modèles stellaires en ajustant dans l'ultraviolet les indices d'absorption mesurés dans les spectres stellaires de 10 amas d'étoiles dans le Grand Nuage de Magellan. Je montre que négliger l'échantillonnage stochastique de la fonction de masse initiale stellaire de ces amas jeunes et peu massifs a une faible influence dans l'estimation d'âge et de métallicité, mais peut entraîner une surestimation significative des estimations de leur masse. Ensuite, je développe une approche basée sur une description épurée des principales caractéristiques du MI, afin de calculer de manière auto-cohérente l'influence combinée de l'émission et de l'absorption de ce milieu dans le spectre ultraviolet des GFE. Ce modèle tient compte du transport radiatif aussi bien à travers les couches intérieures ionisées, qu'à travers les couches extérieures neutres des nuages de formation d'étoiles ainsi que le milieu diffus entre ces nuages. J'utilise cette approche pour étudier la signature enchevêtrée des étoiles, du milieu neutre et du milieu ionisé dans les spectres ultraviolets des GFE. J'obtiens que la plupart des indices stellaires dans l'ultraviolet sont susceptibles de présenter une contamination par le MI qui augmente avec la métallicité. Enfin, j'identifie des raies d'émission et d'absorption interstellaires pouvant discriminer efficacement les différentes phases du MI. / I combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. I start by assessing the reliability of the stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large-Magellanic-Cloud clusters. In doing so, I find that neglecting stochastic sampling of the stellar initial mass function in these young low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, I develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. My model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. I use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. I find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. I also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Quantitative measurements of line intensities have been made since the beginning of the last century. The quantity and quality of the data available have increased drastically with the advent of electronic detectors. However, the data are widely scattered in the literature. In face of this, we compiled a catalog of emission-lines intensities. It contains data on HII regions in 41 galaxies, all totaling approximately 36 000 line intensities. We have constructed a table with 1 750 emission-lines observed, showing their transition probabilities and configurations or terms. We have standardized the identification of all the emission-lines of the catalog based on this table. The database was used for different studies. We checked the values of the ratios [OIII] λ5007/λ4959 and [NII] λ6583/λ6548 with the emission-line ratios from the HII regions in the catalog. The values found are in agreement with the theoretical ones. With the diagram λ6717/Hβ versus λ6731/Hβ, we verified that most of the objets in the catalog are near the low-density limit. We also present a comparison of different temperature indicators based on observational data from HII regions, HII galaxies and planetary nebulae extracted from the literature. We have found that there is not a unique relation between the temperature indicators of different ionization zones which allows a reliable derivation of one of these from another. We have constructed diagnostic diagrams comparing the emission-lines ratios [OI]/Hα, [OII]/Hβ, [OIII]/Hβ, [NII]/Hα, [SII]/Hα e [OII]/[OIII]. For them, we have distinguished the emission-line ratios of HII regions of different galaxies and, for data from our galaxy, we have distinguished different objects. We described the diagnostic diagrams using theoretical grids varying the ionization parameter and the chemical abundance. These were computed using a photoionization code and different spectral energy distributions. With the diagram [NII]/[OII] versus [OIII]/[OII], we have obtained the best separation between ionization parameter and metallicities. We observed large discrepancies between the chemical abundances of the grids of models and those determined from collisionaly excited lines. / Medidas quantitativas de intensidades de linhas de emissão têm sido feitas desde o in´ıcio do século passado. A quantidade e a qualidade dos dados disponíveis têm crescido drasticamente com o advento dos detectores eletrônicos. Porém, os dados estão amplamente espalhados na literatura. Diante disso, compilamos um catálogo de intensidades de linhas de emissão. Este contém dados de regiões HII de 41 galáxias, totalizando aproximadamente 36 000 intensidades de linhas. Construímos uma tabela com 1 750 linhas de emissão observadas, apresentando suas probabilidades de transição e configurações ou termos. Padronizamos a identificação de todas as linhas de emissão do catálogo com base nessa tabela. O banco de dados foi utilizado para diferentes estudos. Checamos os valores das razões [OIII] λ5007/λ4959 e [NII] λ6583/λ6548 com razões de linhas de emissão de regiões HII do catálogo. Os valores encontrados concordam com os teóricos. Com o diagrama λ6717/Hβ versus λ6731/Hβ, verificamos que a maior parte dos objetos do catálogo estão próximos ao limite de baixa densidade. Apresentamos também uma comparação de diferentes indicadores de temperatura baseada em dados observacionais de regiões HII, de galáxias HII e de nebulosas planetárias extraídos da literatura. Encontramos que não há uma única relação entre indicadores de temperaturas de diferentes zonas de ionização que permita uma derivação confiável de uma destas a partir da outra. Construímos diagramas de diagnóstico comparando as razões de linhas [OI]/Hα, [OII]/Hβ, [OIII]/Hβ, [NII]/Hα, [SII]/Hα e [OII]/[OIII]. Para eles, distinguimos as razões de linhas de emissão de regiões HII de galáxias diferentes e, para os dados de nossa galáxia, distinguimos os diferentes objetos. Descrevemos os diagramas de diagnóstico utilizando grades teóricas variando o parâmetro de ionização e a metalicidade. Estas foram calculadas usando um código de fotoionização e diferentes distribuições espectrais de energia. Com o diagrama [NII]/[OII] versus [OIII]/[OII], obtivemos a melhor separação entre o parâmetro de ionização e a metalicidade. Verificamos grandes discrep ancias entre as abundâncias químicas das grades de modelos e aquelas determinadas de linhas excitadas colisionalmente.

Les interactions gaz-grains jouent un rôle important dans la chimie des milieux interstellaires et protoplanétaires. Le paramètre-clé qui gouverne les échanges entre la surface des grains et la phase gazeuse est l’énergie d’adsorption Ea. Ce travail a pour but de développer une approche jointe expérimentale et théorique afin de déterminer les énergies d’adsorption pour des atomes et molécules d’intérêt astrophysique sur des substrats-modèles des surfaces des grains de poussière interstellaires. Expérimentalement, la méthode employée est la désorption programmée en température (TPD). Le travail a contribué en l’établissement d’une méthode de traitement des courbes de désorption, basée sur une distribution d’énergie d’adsorption et utilisant un set limité de données à plusieurs rampes de chauffage, pour déterminer le couple de paramètres de l’équation de Polanyi-Wigner que sont l’énergie d’adsorption et le préfacteur. D’un point de vue de la chimie théorique, les énergies d’adsorption sont déterminées en utilisant la théorie de la fonctionnelle de la densité (DFT) implémentée dans le module Vienna Ab initio Simulation Package (VASP). Cette méthode permet également d’accéder aux géométries d’adsorption, ainsi qu’aux différents sites sur la surface. La méthode expérimentale a été validée par une comparaison avec un système connu : l’adsorption du méthanol CH3OH sur le graphite. L’adsorption des gaz rares Ar/Kr/Xe sur les glaces d’eau a été étudiée comme un cas d’intérêt pour la planétologie. L’adsorption de l’acétonitrile (CH3CN) et de son isomère l’isoacétonitrile (CH3NC) sur les surfaces de graphite, de quartz et de glaces d’eau a également été étudiée, puisque ces deux molécules sont détectées dans le milieu interstellaire. Les énergies d'adsorption trouvées dans le cadre de ce travail seront intégrées dans la base des données KIDA. / Gas-grain interaction plays an important role in the chemistry of the cold interstellar medium and protoplanetary disks. A key parameter for modeling the exchange between grain surfaces and gas phase is adsorption energy, Ea. This work aims to develop a reliable and systematic experimental/theoretical approach to determine the adsorption energies of relevant atoms and molecules on models of interstellar grain surfaces. Employed experimental technique is the Temperature Programmed Desorption. Developed experimental protocol and data treatment technique based on distribution of adsorption energies and use of a set of heating rates enable to determine the coupled parameters of Polanyi-Wigner equation: adsorption energy Ea and prefactor N. Computational chemistry approach, Density Functional Theory (DFT) as implemented in Vienna Ab initio Simulation Package (VASP) is used to get the insight on the behaviour of the surface-adsorbate systems at the atomic level. This approach allows as well to determine adsorption energies. A presence of multiple adsorption sites with different adsorption energies is predicted. Methanol CH3OH adsorption on graphite is used as a known example to validate the technique. Ar/Kr/Xe adsorption on water ice is studied as a case relevant for planetology. Acetonitrile (CH_3CN) and methyl isocyanide (CH_3NC) adsorption on water ice, quartz and graphite is investigated since those two molecules are both detected in the interstellar medium. Adsorption energies determined in this work will be included in KIDA database.

We present a catalog of the neutral atomic hydrogen structures (H I holes) and the analysis of their properties in nearby (≤ 10.3 Mpc) gas-rich dwarf galaxies of the LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey) group. We used high sensitivity (≤ 1.1 mJy beam-1 channel-1), high velocity resolution (1.3 km s-1 to 2.6 km s-1) and high linear resolution (average ~110 pc; angular resolution ~6”) H I data of 37 dwarf irregulars and four blue compact dwarf galaxies. We cataloged H I holes in the entire sample and studied the of the properties of holes. We also investigated the effect of H I porosity on star formation, and the correlation of the star formation rate (SFR) calculated from H I holes with standard star formation tracers Hα and FUV. We detected 306 H I holes in LITTLE THINGS galaxies. We confirmed 22 kpc-sized holes, the largest and the smallest hole diameters are about 2.3 kpc and 38 pc (resolution limit) respectively. The expansion velocities of the holes range from 5 km s-1 (upper limit) to 30 km s-1, and the rotational velocities range from 6 km s-1 to 77 km s-1. The H I disk radii of the galaxies range from about 0.5 kpc to 6.7 kpc. The kinetic ages of the holes range from about 1 to 127 Myr, and the estimated scale heights are varying from 61 pc to 653 pc. The percentage distribution of the holes outside and inside the V-band break radius is nearly uniform, 49% and 51% respectively. In LITTLE THINGS galaxies, we found no obvious correlation between the surface and volume porosities, and SFR. However, two highest and two lowest porosity galaxies have no star formation at present. The holes are consistent with the SFR estimated from the energy required to create a hole and the star formation rates measured from Hα and FUV, indicating that the holes are consistent with a star formation origin.

Les raies d'absorption de quasars sont des outils efficaces pour étudier le milieu interstellaire dans les galaxies. Dans ce travail, nous étudions un échantillon de soixante-six systèmes absorbants à z<1.5 sélectionnés pour la présence de raies d'absorption de CI intenses dans leurs spectres SDSS. Ils sont observés par les spectrographes X-shooter et UVES du VLT de l'ESO. Nous étudions en tout 17 systèmes observés par X-shooter. Nous déduisons la métallicité, la déplétion par la poussière, le taux d'extinction par la poussière et le taux d'absorption des raies de MgII, MgI, CaII et NaI décalées dans l'infrarouge proche. Nous détectons neuf raies d'absorption de CaII avec W(CaII λ3934)>0.23Å. Nous détectons dix raies d'absorption de NaI dans quatorze systèmes susceptibles d'en montrer. La largeur équivalente médiane de W(NaI λ5891)=0.68Å est plus grande que celles observées dans des nuages proches ayant des densités-colonnes de HI similaires ou dans des systèmes CaII à z<0.7 détectés par le SDSS. La présence systématique de raies d'absorption de NaI dans ces systèmes CI suggère fortement que le gaz environnant est neutre et froid, et donc peut faire partie du gaz moléculaire diffus dans le milieu interstellaire de galaxies à fort décalage vers le rouge. Les raies d'absorption de MgII s'étalent sur plus de 400km/s en Δv pour la moitié de l'échantillon; trois systèmes ont un Δv supérieur à 500 km/s. Tout ceci suggère qu'une fraction importante du gaz froid à fort décalage vers le rouge émane d'environnements perturbés. Nous détectons de l'hydrogène moléculaire dans tous les systèmes dans la limite de détection. / Quasar absorption lines are a powerful tool to study the interstellar medium(ISM) in the galaxies. We study a sample of 66 z >1.5 absorbers selected based on the presence of strong CI absorption lines in SDSS spectra and observed with the ESO-VLT spectrograph X-shooter/UVES. I study 17 systems that are re-observed by X-shooter. I derive metallicities, depletion onto dust, extinction by dust and analyse the absorption from MgII, MgI, CaII and NaI that are redshifted into the near infrared wavelength range. I detect 9 CaII absorptions with W(CaII λ3934) > 0.23 Å out of 14 systems. I detect 10 NaI absorptions in the 11 systems where we could observe this absorption. The median equivalent width (W(NaI λ5891) = 0.68 Å) is larger than what is observed in local clouds with similar HI column densities but also in z<0.7 CaII systems detected in the SDSS. The systematic presence of NaI absorption in these CI systems strongly suggests that the gas is neutral and cold, maybe part of the diffuse molecular gas in the ISM of high-redshift galaxies. The MgII absorptions are spread over more than Δv ~ 400 km/s for half of the systems; three absorbers have Δv > 500 km/s. The kinematics is strongly perturbed for most of these systems which probably do not arise in quiet disks and must be close to regions with intense star formation activity. All this suggests that a large fraction of the cold gas at high redshift arises in disturbed environments. We detect molecular hydrogen in all the systems within the detection limit.