We present a recalibration of the M-BH-sigma(star) relation, based on a sample of 16 reverberation-mapped galaxies with newly determined bulge stellar velocity dispersions (sigma(star)) from integral-field spectroscopy (IFS), and a sample of 32 quiescent galaxies with publicly available IFS. For both samples, sigma(star) is determined via two different methods that are popular in the literature, and we provide fits for each sample based on both sets of sigma(star). We find the fit to the active galactic nucleus sample is shallower than the fit to the quiescent galaxy sample, and that the slopes for each sample are in agreement with previous investigations. However, the intercepts to the quiescent galaxy relations are notably higher than those found in previous studies, due to the systematically lower sigma(star) measurements that we obtain from IFS. We find that this may be driven, in part, by poorly constrained measurements of bulge effective radius (r(e)) for the quiescent galaxy sample, which may bias the sigma(star) measurements low. We use these quiescent galaxy parameterizations, as well as one from the literature, to recalculate the virial scaling factor f. We assess the potential biases in each measurement, and suggest f = 4.82 +/- 1.67 as the best currently available estimate. However, we caution that the details of how sigma(star) is measured can significantly affect f, and there is still much room for improvement.

There is mounting evidence that supermassive black holes (SMBHs) form and grow in bulgeless galaxies. However, a robust determination of the fraction of active galactic nuclei (AGNs) in bulgeless galaxies, an important constraint to models of SMBH seed formation and merger-free models of AGN fueling, is unknown, since optical studies have been shown to be incomplete for AGNs in low-mass galaxies. In a recent study using the Wide-field Infrared Survey Explorer, we discovered hundreds of bulgeless galaxies that display mid-infrared signatures of extremely hot dust suggestive of powerful accreting massive black holes, despite having no signatures of black hole activity at optical wavelengths. Here we report X-ray follow-up observations of J122434.66+555522.3, a nearby (z = 0.052) isolated bulgeless galaxy that contains an unresolved X-ray source detected at the 3 sigma level by XMM-Newton with an observed luminosity uncorrected for intrinsic absorption of L2-10 (keV) = (1.1 +/- 0.4) x 10(40) erg s(-1). Ground-based near-infrared spectroscopy with the Large Binocular Telescope and multiwavelength observations from ultraviolet to millimeter wavelengths together suggest that J1224+5555 harbors a highly absorbed AGN with an intrinsic absorption of N-H > 10(24) cm(-2). The hard X-ray luminosity of the putative AGN corrected for absorption is L2-10 keV similar to 3 x 10(42) erg s(-1), which, depending on the bolometric correction factor, corresponds to a bolometric luminosity of the AGN of L-bol 6 x 10(43)-3 x 10(44) erg s(-1). and a lower mass limit for the black hole of M-BH similar or equal to 2 x 10(6) M-circle dot, based on the Eddington limit. While enhanced X-ray emission and hot dust can be produced by star formation in extremely low metallicity environments typical in dwarf galaxies, J1224+5555 has a stellar mass of similar to 2.0 x 10(10) M-circle dot and an above solar metallicity (12 + logO/H = 9.11), typical of our WISE-selected bulgeless galaxy. sample. While collectively. these observations suggest the presence of an AGN, we caution that identifying obscured AGNs in the low-luminosity regime is challenging. and often requires multiwavelength observations. These observations suggest that low-luminosity AGNs can be heavily obscured and reside in optically quiescent galaxies, adding to the growing body of evidence that the fraction of bulgeless galaxies with accreting black holes may be significantly underestimated based on optical studies.

The first chapter assesses the impact of the cohort size on labour market outcomes. Using exogenous variation and micro-level data for France, the UK and the US, we study the effect of supply shocks measured at different ages on unemployment rates and wages during a cohort's life cycle. The results from an IV estimation show that the largest magnitude of the effects is found when the cohort size is measured at age 25. The impact of both wages and unemployment rates are temporary, however, both decreasing with time. The second chapter analyses the effects of large inflows of foreign students on English undergraduates. Our results confirm previous findings that there is no overall effect, but we identify changes in the distribution of natives. We find that top performing English students are crowded in by foreign students. It is also mainly English-born males, natives who do not have English as their mother tongue and those of Asian ethnic origins that are crowded in by foreign students. In chapter three, we aim to understand the short-term effects of changes in the level of the tuition fees charged by English universities on students' geographic mobility. Our results suggest that the increase in tuition fees in 2006/07 charged by English universities led students to enrol into universities that are closer to home, with a larger effect experienced by men and White students. Moreover, we find that students are less likely to move to universities located in rich areas.

Contrary to historic assumptions, bulges in the local Universe present a heterogeneous class of objects. Observations indicate that bulges are bimodal in structure, interstellar medium, stellar populations and dynamical state. Using observations in the UV, optical, near-infrared and mid-infrared we study the nature of local bulge-disk galaxies. The aim is first to find consistent means to differentiate different bulge types. Then we can use these diagnostic methods to study the properties of bulges of each type, thereby better understanding the possible formation mechanisms of each type. Finally, we will use these diagnostic methods to determine how many of each type of bulge exists in the local Universe, and thus understand how the heterogeneity of bulges may affect our understanding of galaxy evolution. Using 3.6-8.0 micron colors we show that dichotomy in bulge morphology is closely tied to the dichotomy in bulge interstellar medium. We find that those bulges with active interstellar medium, per unit stellar mass, have morphological features commonly found in disks (e.g. nuclear spirals, bars and rings). We follow this up with more robust star formation rates, as measured by linear combining UV and 24 micron luminosity, and determine that the boundary is near specific star formation rate ~30 Gyr⁻¹. We also find that the shape of bulge surface brightness profiles correlates well with morphology. When parameterized by a Sérsic function, we find that bulges with n[subscript b]<2 have disk-like morphology and those bulges with n[subscript b]>2 have morphology that is very similar to that of an elliptical galaxy. We thus conclude that bulges with disk-like nuclear morphology, specific star formation rate that is less than 30 Gyr⁻¹, and/or Sérsic index n[subscript b]<2 represents a distinct class of object. We refer to these bulges as "pseudobulges" and the complimentary set of bulges that are inactive, with high Sérsic index, and morphologically like elliptical galaxies is referred to as "classical bulges." We find that a significant amount of evidence points to pseudobulges and classical bulges originating from separate formation mechanisms. First, we rule out the possibility that pseudobulges are the result solely from mass dependent phenomenon. Rather, pseudobulges and classical bulges over lap significantly in mass, luminosity and size. Also, they are found in galaxies of similar mass, luminosity and size. Therefore, pseudobulges are not simply a low-mass phenomenon of the same process. Also, we find that many of the properties of pseudobulges are connected to properties of the outer disk. We find that the half-light radius of pseudobulges correlates linearly with the scale-length of the outer disk. Furthermore, this correlation does not exist for classical bulges. Also, the mass of pseudobulges correlates with the mass of the outer disk. We find that the star formation rate density of pseudobulges is a function of the stellar mass of the exponential outer disk such that pseudobulges with high star formation rate densities only occur more massive stellar disks. Thus it appears that both structure and growth of pseudobulges is a function of the properties of the outer disk. However, classical bulges do not show the same correlations. Also, we find that the star formation rate density of pseudobulges positively correlates with the mass density, classical bulges do not show an analogous correlation. If secular growth were responsible for the formation of pseudobulges, such a correlation should exist. Furthermore, we find that the specific star formation rates of most pseudobulges are high enough to account for the stellar mass within the typical ages of disk (~10 Gyr). We also show that classical bulges participate in the same structural parameter correlations as elliptical galaxies. Just like elliptical galaxies, as classical bulges become brighter they also become larger in radius, lower in surface density, and have higher Sérsic index. However pseudobulges behave very differently. There is little-to-no correlation between the size of pseudobulges and the luminosity, surface brightness or Sérsic index. We stress that this observation extends of 9 magnitudes in brightness. Therefore the size of pseudobulges, has thus far only been found to correlate with the size of the outer disk. Furthermore we find that pseudobulges show a positive correlation between surface density and luminosity. The behavior of pseudobulges in these parameter correlations implies that they are not virialized stellar systems that have experienced violent relaxation. Thus it is likely that the formation of pseudobulges is not like that of elliptical galaxies and classical bulges. Furthermore, the connection between pseudobulge properties and those of their associated outer disk seem to favor long-term growth that is more likely to be driven by disk processes, commonly called "secular evolution." Finally we show that the dichotomy of bulge types has a strong influence on our understanding of galaxy evolution. We find that global galaxy properties are tied to the bulge dichotomy. Galaxies with pseudobulges are found to be in "blue sequenc" galaxies and those with classical bulges are found to be in "red sequence" galaxies. A large body of literature has shown that blue and red galaxies appear to be distinct classifications of galaxies. The correlation with bulge type implies that the bulge dichotomy may be also be a consequence of the bimodal nature of galaxy evolution. Finally, we show that in the local Universe pseudobulges are by far the most common type of massive galaxy. We find that only 17% of galaxies have a detectable classical bulge. Also we show that over 3/4 of the star formation in spiral and elliptical galaxies in the local Universe occurs in galaxies with pseudobulges. Thus understanding pseudobulges is a necessary step to understanding the processes that have lead to the population of galaxies in the nearby Universe. / text

We report the identification of a bright hard X-ray source dominating the M31 bulge above 25 keV from a simultaneous NuSTAR-Swift observation. We find that this source is the counterpart to Swift J0042.6+4112, which was previously detected in the Swift BAT All-sky Hard X-ray Survey. This Swift BAT source had been suggested to be the combined emission from a number of point sources; our new observations have identified a single X-ray source from 0.5 to 50 keV as the counterpart for the first time. In the 0.5-10 keV band, the source had been classified as an X-ray Binary candidate in various Chandra and XMM-Newton studies; however, since it was not clearly associated with Swift J0042.6+4112, the previous E < 10 keV observations did not generate much attention. This source has a spectrum with a soft X-ray excess (kT similar to 0.2 keV) plus a hard spectrum with a power law of Gamma similar to 1 and a cutoff around 15-20 keV, typical of the spectral characteristics of accreting pulsars. Unfortunately, any potential pulsation was undetected in the NuSTAR data, possibly due to insufficient photon statistics. The existing deep HST images exclude high-mass (> 3 M-circle dot) donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass (< 3 M-circle dot) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.

We present a combined morphological and X-ray analysis of Was. 49, an isolated, dual-AGN system notable for the presence of a dominant AGN, Was 49b, in the disk of the primary galaxy, Was 49a, at a projected radial distance of 8. kpc from the nucleus. Using X-ray data from Chandra, the Nuclear Spectroscopic Telescope Array, and Swift, we find that this AGN has a bolometric luminosity of L-bol similar to 10(45) erg s(-1), with a black hole mass of M-BH = 1.3(-0.9)(+10)M(circle dot) . Despite the large mass, our analysis of optical data from the Discovery Channel Telescope shows that the supermassive black hole (SMBH) is hosted by a stellar counterpart with a mass of only 5.6(-2.6)(+4.9)M(circle dot), which makes the SMBH potentially larger than expected from SMBH-galaxy scaling relations, and the stellar counterpart exhibits a morphology that is consistent with dwarf elliptical galaxies. Our analysis of the system in the r and K bands indicates that Was. 49 is a minor merger, with the mass ratio of Was 49b to Was 49a between similar to 1:7 and similar to 1:15. This is in contrast with findings that the most luminous merger-triggered AGNs are found in major mergers and that minor mergers predominantly enhance AGN activity in the primary galaxy.

Decades of research on compression ignition engines have led to a highly efficient combustion cycle in contemporary diesel engines. Nonetheless, the combustion process is being studied perpetually to meet both current and future emission regulations. One of the most influential parameters that impacts the combustion quality, is the fuel spray evolution during injection, and subsequent fuel-air mixture formation inside the engine cylinder. The spray evolution has been investigated to a high level of detail, and the highly complex processes of mixture formation and combustion are well-documented for diesel engines. Most of these investigations are limited to studying either research-grade injectors, or brand new production injectors. Injectors in real-world diesel engines, i.e. normal passenger cars and trucks that are used on a daily basis, are however subject to deposit formation at the tip of the injector nozzle. These deposits have the potential of altering the internal nozzle flow and fuel spray pattern, which in turn degrades combustion quality and increases engine emissions. In the work presented in this thesis the spray evolution of production injectors has been studied over a wide range of injector conditions. Common rail light-duty injectors with a usage history of up to 90 000 miles were acquired from the UK commuter car parc, and several brand new injectors were studied for comparison purposes. It is shown that the spray pattern of the injected fuel changes over the lifetime of the injector. For used injectors a reduced penetration rate was observed in the transient regime of fuel injection, during needle lift. The reduced penetration rate was often accompanied by anomalous radial expansions. Although the magnitude of the effects varied from injector to injector, the highest mileage injectors tended to produce the strongest spray deviations. For several high-mileage injectors the end of injection appeared retarded with respect to new injectors. Expulsions of liquid ligaments and droplets after the end of injection were observed from all injectors, irrespective of the mileage of the injector.

Les bulbes sont présents dans environ 80% des galaxies spirales locales de masse intermédiaire. Les galaxies spirales représentent environ 70% des galaxies de masse intermédiaire (typiquement avec des masses comprises entre 2 × 10^10 et 10^11 masses solaires) de l’Univers local. Alors que les bulbes classiques sont généralement associés aux résultats de fusions, les pseudo-bulbes sont plutôt associés à l’évolution séculaire. Cependant, le modèle cosmologique ΛCDM prévoit une croissance hiérarchique des galaxies par les fusions alors que l’on trouve plus de 50% de pseudo-bulbes dans les galaxies spirales de masse intermédiaire de l’Univers local. Le but de la thèse est de vérifier s’il est possible de construire des pseudo-bulbes à partir de fusions majeures riches en gaz. La première partie de cette thèse est consacrée à la présentation du sujet ainsi qu’à l’état de l’art sur la formation et l’évolution des bulbes galactiques.La deuxième partie de cette thèse porte sur la description de la méthodologie mise en place pour analyser les bulbes des galaxies spirales et comprendre leur formation. La thèse com- porte deux axes d’études, une partie observationnelle avec l’analyse de deux échantillons complets de galaxies spirales locales de masse intermédiaire pour déterminer la proportion de pseudo-bulbes dans ces échantillons et avoir une référence robuste. Une autre partie, qui est le coeur de l’étude, est dédiée à l’analyse de simulations numériques de fusions majeures de deux progéniteurs riches en gaz réalisées avec un code N-body/Hydrodynamique (GADGET2). L’objectif est de reproduire ce type de galaxies et d’étudier leurs propriétés grâce à une décomposition bulbe+disque.Dans la troisième partie, je montre que, dans les limites données par les simulations, nous pou- vons reproduire des galaxies spirales présentant des pseudo-bulbes via des fusions majeures riches en gaz. Cette thèse propose un nouveau scénario de formation des pseudo-bulbes grâce à la formation de barres durant les fusions majeures qui permet d’amener du gaz dans les parties centrales. De plus, beaucoup de structures observées comme des barres, anneaux ou double-disques sont reproduits dans les simulations. Les différents paramètres des simulations ont ensuite été modifiés (fraction de gaz, rapport de masses, masse des progéniteurs, feedback, extension du gaz, pericentre) pour explorer leur impact sur les résultats. On constate que les disparités des indices de Sersic et des rapports B/T proviennent autant de la différence entre les orbites que de celle entre les paramètres physiques initiaux choisis pour les simulations, mais certaines grandes tendances peuvent tout de même être extraites. Par exemple, l’étude montre que plus la fraction de gaz des progéniteurs est élevée, plus les indices Sersic et le rapport B/T diminuent, plus le nombre de barres et leur taille augmentent. / Bulges are present in almost 80% of nearby spiral galaxies of intermediate mass. Spiral galaxies represent about 70% of the intermediate-mass galaxies (typically with a mass between 2 × 10^10 and 10^11 solar masses) in the local Universe. While classical bulges have been associated to the result of major mergers, pseudo-bulges have been rather associated to secular evolution. However, the cosmological ΛCDM model predicts a hierarchical growth of galaxies via mergers while pseudo-bulges are found in > 50% of large nearby spiral galaxies. The aim of this thesis is to verify if we can build pseudo-bulges with gas-rich major mergers. The first part of this thesis is devoted to the presentation of the subject and the state of the art on the formation and evolution of galactic bulges.The second part of this thesis is focusing on the methodology developped to analyse bulges of spiral galaxies and understand their formation. The thesis has two axes of study, an observational part with the analysis of two complete samples of local spiral galaxies of intermediate mass to determine the proportion of pseudo-bulges in these samples and to have a reliable reference. Another part, which is the core of the study, is dedicated to the analysis of nume- rical simulations of gas-rich major mergers done with a N-body / SPH code (GADGET2). The aim is to reproduce this type of galaxy and to study their properties thanks to a bulge + disk decomposition.In the third part, I show that, within the limits given by the simulations, we can reproduce spiral galaxies with pseudo-bulges via gas-rich major mergers. This thesis propose a new scenario of pseudo-bulge formation thanks to the formation of a bar, which bring gas into the central parts. In addition, most of the observed structures, such as bars, rings or double-disks, are reproduced in the simulations. The different parameters of simulations has been then modified (gas fraction, mass ratio, mass of progenitors, feedback, gas extension, pericenter) to explore their impact on the results. We found that the disparities on Sersic index and B/T ratio comes as much from the difference between orbits as from between initial physical parameters chosen for simulations but we can still extract some trends. For instance, I show that the higher the gas fraction of the progenitors, the lower the Sersic index and the B/T ratio, the more the number of bars and their size increases.

Cette thèse a pour but de faire le lien entre l’évolution des galaxies, leur morphologie et les processus physiques internes, notamment la formation stellaire comme le résultat du milieu interstellaire turbulent et multiphase, en utilisant les simulations cosmologiques zoom-in, les simulations des galaxies isolées et en interaction, et le modèle analytique de la formation stellaire. Dans le chapitre 1, j’explique la motivation pour cette thèse et je passe brièvement en revue le contexte nécessaire lié à la formation des galaxies et la modélisation en utilisant les simulations numériques. Tout d’abord, j’explore l’évolution de la morphologie des galaxies du type de la Voie Lactée dans la série des simulations cosmologiques zoom-in à travers l’analyse des barres. J’analyse l’évolution de la fraction des barres avec le redshift, sa dépendance en fonction de la masse stellaire et l’histoire d’accrétion de galaxies individuelles. Je montre en particulier, que la fraction de barres décroit avec le redshift croissant, en accord avec les observations. Ce travail montre également que les résultats obtenus suggèrent que l’époque de la formation des barres correspond à la transition entre une phase précoce “violente” de la formation de galaxies spirales à z > 1, pendant laquelle elles sont souvent perturbées par les fusions avec les galaxies de masse comparable ou par multiple fusions avec les galaxies de petite masse, mais aussi les instabilités violentes de disque, et une phase "séculaire" tardive à z < 1, quand la morphologie finale est généralement stabilisée vers une structure dominée par le disque. Cette analyse est présentée dans le chapitre 2. Étant donné que ces simulations cosmologiques forment trop d'étoiles trop tôt par rapport aux populations de galaxies observées, je me concentre dans le chapitre 3 sur la formation stellaire dans un échantillon de simulation de galaxies en isolation, à bas redshift, et à résolution du parsec et sous-parsec. J'étudie l'origine physique de leurs relations de formation stellaire avec les cassures, et montre que le seuil de densité surfacique pour une formation stellaire efficace peut être lié à la densité caractéristique d'apparition de turbulence supersonique. Ce résultat s'applique aussi bien aux galaxies qui fusionnent, dans lesquelles l'augmentation de la turbulence compressive déclenchée par les marées compressives les conduit au régime de sursaut de formation d'étoiles. Un modèle analytique idéalisé de formation stellaire liant la densité surfacique de gaz au taux de formation stellaire comme une fonction de la présence de turbulence supersonique et la structure associée du milieu interstellaire est ensuite présenté dans le chapitre 4. Ce modèle prédit une cassure à basse densité de surface qui est suivie par un régime de loi de puissance à haute densité dans différents systèmes en accord avec les relations de formation stellaire des galaxies observées et simulées. La dernière partie de cette thèse est dédiée à la technique alternative de zoom-in cosmologique (Martig et al. 2009) et son implémentation dans le code à raffinement de maillage adaptatif RAMSES. Dans le chapitre 5, je présente les caractéristiques de base de cette technique aussi bien que certains de nos tout premiers résultats dans le contexte de l'accrétion cosmologique diffuse. / This thesis aims at making the link between galaxy evolution, morphology and internal physical processes, namely star formation as the outcome of the turbulent multiphase interstellar medium, using the cosmological zoom-in simulations, simulations of isolated and merging galaxies, and the analytic model of star formation. In Chapter 1, I explain the motivation for this thesis and briefly review the necessary background related to galaxy formation and modeling with the use of numerical simulations. I first explore the evolution of the morphology of Milky-Way-mass galaxies in a suite of zoom-in cosmological simulations through the analysis of bars. I analyze the evolution of the fraction of bars with redshift, its dependence on the stellar mass and accretion history of individual galaxies. I show in particular, that the fraction of bars declines with increasing redshift, in agreement with the observations. This work also shows that the obtained results suggest that the bar formation epoch corresponds to the transition between an early "violent" phase of spiral galaxies formation at z > 1, during which they are often disturbed by major mergers or multiple minor mergers as well as violent disk instabilities, and a late "secular" phase at z < 1, when the final morphology is generally stabilized to a disk-dominated structure. This analysis is presented in Chapter 2. Because such cosmological simulations form too many stars too early compared to observed galaxy populations, I shift the focus in Chapter 3 to star formation in a sample of low-redshift galaxy simulations in isolation at parsec and sub-parsec resolution. I study the physical origin of their star formation relations and breaks and show that the surface density threshold for efficient star formation can be related to the typical density for the onset of supersonic turbulence. This result holds in merging galaxies as well, where increased compressive turbulence triggered by compressive tides during the interaction drives the merger to the regime of starbursts. An idealized analytic model for star formation relating the surface density of gas and star formation rate as a function of the presence of supersonic turbulence and the associated structure of the ISM is then presented in Chapter 4. This model predicts a break at low surface densities that is followed by a power-law regime at high densities in different systems in agreement with star formation relations of observed and simulated galaxies. The last part of this thesis is dedicated to the alternative cosmological zoom-in technique Martig et al. 2009 and its implementation in the Adaptive Mesh Refinement code RAMSES. In Chapter 5, I will present the basic features of this technique as well as some of our very first results in the context of smooth cosmological accretion.