<p>There is by now compelling evidence that most of the matter in the universe is in the form of dark matter, a form of matter quite different from the matter we experience in every day life. The gravitational effects of this dark matter have been observed in many different ways but its true nature is still unknown. In most models dark matter particles can annihilate with each other into standard model particles. The direct or indirect observation of such annihilation products could give important clues for the dark matter puzzle. For signals from dark matter annihilations to be detectable, typically high dark matter densities are required. Massive objects, such as stars, can increase the local dark matter density both via scattering off nucleons and by pulling in dark matter gravitationally as the star forms. Dark matter annihilations outside the star would give rise to gamma rays and this is discussed in the first paper. Furthermore dark matter annihilations inside the star would deposit energy inside the star which, if abundant enough, could alter the stellar evolution. Aspects of this are investigated in the second paper. Finally, local dark matter overdensities formed in the early universe could still be around today; prospects of detecting gamma rays from such clumps are discussed in the third paper.</p> / Introduktionsdelen till en sammanläggningsavhandling

L'étude du processus de nucléation des bulles dans les magmas rhyolitiques a été abordée au cours de cette thèse. Des expériences de décompression isothermes en autoclave à chauffage externe et trempe rapide ont été réalisées afin de mieux comprendre : (1) les effets de différentes populations cristallines sur la cinétique de nucléation des bulles d'eau, et (2) les effets du CO2 sur la nucléation homogène des bulles. L'objectif ultime de nos travaux était d'identifier les paramètres texturaux qui pourraient constituer des marqueurs robustes de la dynamique d'ascension des magmas rhyolitiques. Le résultat majeur de cette étude est la démonstration que la relation très forte entre [dP/dt] et n3D tient aussi dans le cas de la nucléation hétérogène. La principale implication volcanologique est que l'étude texturale des ponces naturelles pourrait servir à des applications vélocimétriques et fournir des renseignements sur la dynamique d'ascension des magmas dans les conduits volcaniques

L'approche principalement géochimique menée (éléments majeurs et en trace, 87Sr/86Sr, 143Nd/144Nd, etdelta 18O) a montré que : tout au long de l'histoire de l'Islande, le gradiant géothermique résultant de l'interaction ride-panache mantellique favorise la genèse des magmas acide par fusion partielle de la croûte métabasaltique au centre de l'île et par cristallisation fractionnée en périphérie. En se basant sur le point précédent et des échantillons datés, un modèle d'évolution géodynamique de l'Islande a pu être établit afin de rendre compte de la largeur anormalement élevée de l'île. La comparaison des roches acides (roches "continentales") émises en Islande, à Hawaï et à Kerguelen, avec celles de la croûte continentale primitive (TTG) a montré que les plateaux océaniques n'ont pas été un environnement favorable lors de la genèse de la croûte primitive.

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The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with the surrounding large-scale structures. In this work, we aim to identify the galaxy and cluster quantities that most strongly predict the central galaxy alignment phenomenon among a large parameter space with a sample of 8237 clusters and 94 817 members within 0.1 < z < 0.35, based on the red-sequence Matched-filter Probabilistic Percolation cluster catalogue constructed from the Sloan Digital Sky Survey. We first quantify the alignment between the projected central galaxy shapes and the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, we investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. We find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centring probability, and redder colour. Satellites with redder colour, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation towards their central galaxy major axes. Finally, we provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.

Cosmological hydrodynamic simulations have shown that galaxies are fed by dense, cold gas streams at high redshift. However, the presence of such gas has never been observationally confirmed. Using the Horizon- MareNostrum simulation, I examined whether cold flows are detectable with low-ionisation metal absorption lines, such as C II 1334. It is concluded that due to their low metallicity and density, it is extremely difficult to prove/disprove the presence of cold flows using the metal absorption lines. Revisiting the acquisition of angular momentum in disc galaxies using high resolution simulations, I found that at the time of accretion, gas and dark matter do carry a similar amount of specific angular momentum which is systematically and significantly higher (at minimum by a factor of 2) than that of the dark matter halo as a whole. Whereas cold streams directly deposit this large amount of angular momentum within a sphere of radius r~0.1 Rvir, dark matter particles easily pass through the central region, depositing their angular momentum over a much more spatially extended region. As a result, in our simulations neither the total specific angular momentum of the baryons nor its radial profile ever follows that of the virialised dark matter halo, contrary to what is typically assumed in the standard theory of disc galaxy formation. In order to better understand the formation of disc galaxies and the missing baryon problem in a LCDM universe, continuous, collective galactic winds are implemented. It is demonstrated that stellar feedback processes are able to suppress star formation by ~30% at z=3, compared to that from the run without feedback sources, but it still produces an unrealistic central peak in the rotation curve. Although inclusion of hypernovae further suppresses star formation, it is unable to quench the formation of low-angular momentum stars enough to remove the peaked rotation curves at high redshift. Finally, feedback from active galactic nuclei turns out to be effective at suppressing star formation in massive galaxies at 1<z<2, reproducing their observed number densities in the redshift range. However, further suppression of residual star formation is required to form quiescent galaxies at z=2.

Thesis advisor: Kevin Newmark / Herein, the universe of Charles Baudelaire is explored in light of his relationship to the city of Paris. The circumstances of Baudelaire's life necessitated that he seek refuge from the realm of reality in a realm of imagination. The construction of this universe is examined through relevant historical discussion and analysis of several of Baudelaire's works. These works include selections from his Tableaux Parisiens as well as from his prose poetry. / Thesis (BA) — Boston College, 2004. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: College Honors Program.

>Magister Scientiae - MSc / Next-generation surveys of the large-scale structure of the Universe will be of great importance in allowing us to extract invaluable information about the nature of the Universe and the physical laws that govern it, at a higher precision than previously possible. In particular, they will allow us to more closely study primordial non-Gaussianity, a feature which leaves an imprint on the power spectrum of galaxies on the ultra-large scales and which acts as a powerful probe of the physics of the early Universe. To investigate the extent to which upcoming surveys will be able to improve our knowledge of primordial non-Gaussianity, we perform a forecast to predict the observational constraints on local-type primordial non-Gaussianity, as well as an extension that includes a scale dependence. We study the constraining power of a multi-tracer approach, where information from different surveys is combined to help suppress cosmic variance and break parameter degeneracies. More specifically, we consider the combination of a 21cm intensity mapping survey with each of two different photometric galaxy surveys, and also examine the effect of including CMB lensing as an additional probe. The forecast constraint from a combination of SKA1, a Euclid-like (LSST-like) survey and a CMB Stage 4 lensing experiment is (fNL) ' 0:9 (1:4) which displays a factor of 2 improvement over the case without CMB lensing, indicating that the surveys considered are indeed complementary. The constraints on the running index of the scale-dependent model are forecast as (nNL) ' 0:12 (0:22) from the same combination of surveys.