This thesis presents the CfAIR2 data set, which includes over 4000 near-Infrared (NIR) \(JHK_s\)-band measurements of 104 Type Ia Supernovae (SN Ia) observed from 2005-2011 using PAIRITEL, the 1.3-m Peters Automated InfraRed Imaging TELescope at the Fred Lawrence Whipple Observatory (FLWO) on Mount Hopkins, Arizona. While the discovery of dark energy and most subsequent supernova cosmology has been performed using optical and Ultraviolet wavelength observations of SN Ia, a growing body of evidence suggests that NIR SN Ia observations will be crucial for future cosmological studies. Whereas SN Ia observed at optical wavelengths have been shown to be excellent standardizeable candles, using empirical correlations between luminosity, light curve shape, and color, the CfAIR2 data set strengthens the evidence that SN Ia at NIR wavelengths are essentially standard candles, even without correction for light-curve shape or for reddening. CfAIR2 was obtained as part of the CfA Supernova Program, an ongoing multi-wavelength follow-up effort at FLWO designed to observe high-quality, densely sampled light curves and spectra of hundreds of low-redshift SN Ia. CfAIR2 is the largest homogeneously observed and processed NIR data set of its kind to date, nearly tripling the number of individual \(JHK_s\) band observations and nearly doubling the set of SN Ia with published NIR light curves in the literature. Matched only by the recently published Carnegie Supernova Project sample, CfAIR2 complements the large and growing set of low-redshift optical and NIR SN Ia observations obtained by the CfA and other programs, making this data set a unique and particularly valuable local universe anchor for future supernova cosmology. / Astronomy

Type Ia supernovae (SNe Ia) have proven to be extremely useful for measuring cosmological distances and were used for the discovery of the accelerated expansion of the universe. Although thousands of SNe Ia have been observed to date, many questions surrounding the physics of the explosions and the nature of their progenitor systems remain unanswered. An notable property of many SNe Ia is the relation between extinction due to dust and their colour. For example SN 2014J, the nearest SN Ia in recent years, has an extinction relation which would be very unusual to observe in the Milky Way. One possible explanation to the peculiar extinction could be the presence of circumstellar (CS) dust surrounding the explosions. Incidentally, some proposed progenitor models of SNe Ia suggest that the explosions are surrounded by shells of matter, which could account for the unusual extinction. CS gas would be ionised, if it is exposed to the intense ultraviolet (UV) radiation of a SN Ia. The research presented in this thesis focuses on the search for CS gas by observing the effects of photoionisation on absorption lines commonly detected in optical spectra. Simple models suggest that the frequently studied sodium doublet (Na I D) should significantly decrease or even disappear if the gas is in the CS environment. Conversely, the absence of variations implies that the absorbing gas clouds must be far from the explosion, in the interstellar medium (ISM). To date, few SNe Ia have been shown to have variable absorption lines, to which we have added another case with SN 2013gh. Yet, we have also shown that most observations searching for variable absorption lines have been taken at too late phases, when most CS gas will have already been ionised. Setting out to obtain the earliest possible coverage of a SN Ia with high-resolution spectra, we have been able to set strong limits on the presence of CS gas surrounding SN 2017cbv. Along with evidence from other observational methods, these results have shown that there is little matter in the CS environments of SNe Ia, suggesting that the peculiar extinction likely results from the dust properties of their host galaxy ISM. Although the progenitor question cannot be resolved by these observations, nondetections of CS gas point to models which do not deposit large amounts of matter in their surroundings. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Submitted.</p>

20 supernovae that spectroscopically match the peculiar, superluminous type Ia supernova 2003fg are studied in this project. SN2003fg is thought to have erupted at a super-Chandrasekhar mass, thus breaching the theoretical mass limit for a white dwarf. By analysing the lightcurves of these 20 supernovae, this work aims to understand what the progenitor binary systems from which the supernovae erupt looked like. A lightcurve fitting using the software snpy is performed for each supernova. Using the produced models, time of maximum luminosity, stretch and maximum magnitudes in the g-, r- and i-bands are found. It is found that subluminous supernovae might be a sign of circumstellar material surrounding the progenitor star, though some of the supernovae were superluminous and some adhered to Phillip's relationship. Substructures were found in the lightcurves, as the sampled supernovae showed clearly different behaviours in each of the three bands.

Vers la fin des années 1990, l’utilisation des supernovae de type Ia (SNe Ia) comme indicateurs de distance a permis de mettre en évidence l’expansion accélérée de l’univers. Depuis lors, des campagnes d’observations de grandes envergures ont permis d’augmenter de façon significative le nombre de SNe Ia observées, mais les incertitudes systématiques liées à la qualité des échantillons de SNe Ia proches restent un facteur limitant sur la précision des mesures actuelles. C’est dans le but de réduire ces incertitudes que le projet the Nearby Supernova Factory (SNfactory), à l’aide d’un instrument spectro-photométrique dédié à l’observation des SNe Ia (the Supernova Integral Field Spectrograph), a collecté depuis 2004 plus de 3000 spectres de près de 200 SNe Ia proches. Une des limitations actuelles de leur utilisation, outre les aspects liés aux problèmes d’inter-calibration entre les différentes expériences, est celle du mélange des différentes composantes de leurs variabilités lors de la standardisation empirique de leur module de distance. Une meilleure séparation de ces composantes, ainsi que la découverte de nouveaux indicateurs de distance, font partie des améliorations que peut apporter un échantillon spectral de SNe Ia proches tel que celui de la collaboration SNfactory. Cette thèse de doctorat, effectuée à l’Institut de Physique Nucléaire de Lyon et au Lawrence Berkeley National Laboratory, s’inscrit directement dans cette problématique, en se concentrant sur la mesure d’indicateurs spectraux sur l’échantillon spectral de la collaboration Snfactory. Le plan de cette thèse est le suivant : La première partie présente le contexte scientifique ainsi que l’échantillon de SNe Ia de la collaboration SNfactory utilisé dans les analyses. La deuxième partie se concentre sur la méthode de mesure d’indicateurs spectraux appliquée à l’échantillon spectrale présenté, ainsi que sur une étude de leur sensibilité à l’extinction par le milieu interstellaire. La troisième partie est une étude des corrélations des indicateurs spectraux et de leur utilisation pour la standardisation des Sne Ia. Dans la dernière partie, une utilisation de ces indicateurs spectraux pour la détermination d’une loi d’extinction moyenne est présentée / One of the current limitations of type Ia supernovae used as distance indicators is themixing of their different sources of variabilitiy during the empirical standardization of their distance modulus. Using the nearby SNe Ia spectral sample observed by the Nearby Supernovae Collaboration with the instrument SNIFS (Supernovae Intergral Field Sperctrograph), this thesis mainly focuses on this problematic using spectral indicators measurements. The first part of the thesis presents the scientific context as well as the sample used in the analysis. The second part focus on the spectral indicators measurement and their properties in the presence of interstellar dust extinction. The third part is a study of spectral indicators correlations and their use as standardization parameters. In the last part, we use these spectral indicators to construct a mean extinction law for type Ia supernovae

Les supernovae de type Ia (SNe Ia) sont de puissants indicateurs de distance cosmologique. Elles sont à l'origine de la découverte de l'énergie noire dans l'univers et restent aujourd'hui la meilleure méthode pour contraindre son équation d'état. Cependant, nous ignorons toujours le phénomène exact donnant naissance à ces supernovae. Notamment, nous ne connaissons pas l'influence de l'évolution des paramètres stellaires avec le redshift sur la luminosité de ces objets et donc sur les ajustements cosmologiques. De récentes études ont mis en évidence évidence des biais environnementaux ayant un impact significatif sur les mesures des paramètres cosmologiques. Cependant, ces études analysent les hôtes des SNe Ia dans leur globalité en négligeant les variations pourtant connues des propriétés stellaires et gazeuses au sein de ces galaxies. ! Dans cette thèse je montre comment les données de spectrographie à champ intégral de la collaboration The Nearby Supernova Factory permettent l'étude de l'environnement immédiat (~kpc) de la SNe Ia. Dans une première partie, j'introduis les bases physiques et le contexte scientifique dans lesquels ma thèse s'inscrit. Dans la seconde partie, je commence par détailler les techniques d'extraction des données environnementales locales et, une fois ces données extraites, je développe la mesure du taux de formation stellaire environnant les SNe Ia à partir du signal Hα. Dans mon analyse, je montre comment les propriétés des SNe Ia, et notamment leur luminosité standardisée, dépendent de la présence de formation stellaire à proximité. Ce biais, duquel découlent les biais environnementaux précédemment évoqués, a un impact significatif sur la cosmologie. En se basant sur les évolutions des propriétés stellaires des galaxies, je construit un modèle d'évolution de la luminosité moyenne des SNe Ia en fonction du redshift pour estimer cet impact; les données de la littérature semblent confirmer mes hypothèses. Ces résultats ont été publiés dans le journal européen Astronomy & Astrophysics (Rigault et al. 2013). Dans une troisième partie, je présente des analyses supplémentaires sur l'environnement local des SNe Ia et je suggère de nouvelles approches. ! Cette thèse a mis en évidence un biais environnemental important sur les propriétés des SNe Ia que seule l'analyse locale permet d'aborder. Cette découverte est une étape importante dans la compréhension de ces objets et dans l'amélioration de leur utilisation cosmologique / Type Ia supernovae (SNe Ia) are powerful cosmological distance indicators. They were key tools for the discovery of the accelerating expansion of the Universe and today they remain the strongest demonstrated technique for measuring the dark-energy equation of state. However, a major issue remains: despite decades of study, their progenitors are as yet undetermined. Notably, we still ignore the influence of the redshift-evolution of stellar properties on the absolute luminosity of the SNe Ia and therefore on the fitted cosmological parameters. Recent studies have highlighted potential biases correlated with the global properties of their host galaxies, large enough to induce systematic errors into cosmological measurements if not properly treated. However, those studies analyse hosts of Type Ia supernovae globally thus neglecting the known stellar and gas property variations across galaxies. ! In this thesis, I show how integral field spectroscopy data from the Nearby Supernova Factory allow the study of the local environment of the SNe Ia (~kpc). In the first part of this document, I introduce the physical principals and the scientific context of this work. In a second part, I start by detailing the technical extraction tools developed in order to extract the local host properties. Then, I show how one could measure the star formation activity in the SN vicinity from those data. I focus the analysis on this star formation activity and notably I show how the SNe Ia properties -- particularly their standardised Hubble residuals -- depend on the local host environment, which corresponds to a significant cosmological bias. I finish this second part by introducing a simple model based on the known evolution of the galactic star formation activity. This model enables me to estimate the potential influence of the aforementioned environmental bias on cosmology. I also show that this model can be tested using public data and a first analyses tend to confirm our hypotheses. Those results have been published in Astronomy & Astrophysics (Rigault et al. 2013). The third and last part of the document introduces new approaches and future work perspectives. ! In this thesis, I have highlighted significant environmental biases in SNe Ia properties, thanks to the local approach. However, those biases are less an issue for the cosmological analyses using Type Ia supernovae than a new opportunity to improve them as cosmological probes. ! This Document is written in French. The figures are in English