Universiẗat, Diss., 2002--München.

We have observed two high -redshift quasars with the echelle spectrograph and 2D- Frutti Photon Counter at Las Campanas, in order to investigate the statistical properties of the Lyman -a forest. The two-point correlation function for the Lyman -a forest lines at z .^s 3 is consistent with zero, for all velocity splittings A > 50 km /sec. When Lyman -a lines and other metal lines from known metalline systems are included, the correlation function shows a weak non -zero signal at small A . We suggest that the weak clustering of the Lyman -a forest detected by other workers may be the result of contamination by a small number of metal -line systems and their associated Lyman -a lines.

Galaxy formation is one of the central problems of Physical Cosmology. Neutral hydrogen plays an important role, linking the collapse of cooling gas into haloes with the formation of stars. Lyman alpha, hydrogen's strongest spectral line, can directly probe neutral hydrogen in the high redshift Universe. Lyα can be observed in absorption in Damped Lyman Alpha systems (DLAs): high Hi column density regions that dominate the neutral gas content of the Universe between z ~ 0-5. Lyα in emission is an important signature of early, starforming galaxies. Both populations, however, present significant theoretical challenges. As part of my thesis, I have developed a Monte Carlo Lyα radiative transfer code to investigate models of early galaxies. Rauch et al. (2008) performed an ultra-deep spectroscopic survey and discovered a new population of very faint, spatially extended Lyα emitters, which they claimed to be the long-sought host galaxies of DLAs at z ~ 3. I show here that a simple analytical model, which reproduces the incidence rate and kinematics of DLAs in the context of λCDM models for structure formation, also reproduces the size distribution of the faint Lyα emitters for plausible parameters, which supports their identification as DLA host galaxies. The model suggests that galaxies in haloes with vc ~ 100-150 km s-1 account for the majority of DLA host galaxies, and that these galaxies at z ~ 3 are the building blocks of typical present-day galaxies like our Milky Way. I further use my newly developed Lyα code to perform detailed 1D radiative transfer calculations, investigating the spatial and spectral distribution of Lyα emission due to star formation at the centre of DLAs, and its dependence on the spatial and velocity structure of the gas. The modelling reproduces the observed properties of both DLAs and the faint Lyα emitters, including the velocity width and column density distribution of DLAs and the large observed spatial extent of the faint emitters. In the model, haloes hosting DLAs retain up to 20% of the cosmic baryon fraction in the form of neutral hydrogen. The scattering of Lyα photons at the observed radii, which can be as large as 50 kpc, requires the bulk velocity of the gas at the centre of the haloes to be moderate. I furthermore perform 3D Lyα radiative transfer simulations, building on numerical simulations of galaxy formation that include galactic winds and gas infall. The Lyα emission region is shown to be larger and smoother than the cross-section for damped absorption by ~ 50%, with Lyα photons scattered effectively by gas with column densities >~ 1017 cm⁻². The spectra typically show two peaks, with the relative strength of the red (blue) peak being a reflection of the relative contribution of outflow (inflow) in the velocity profile. There is considerable variation in the observed line profile and spectral intensity with viewing angle. These more realistic models support many of the simplifying assumptions of my previous models, and have the potential to probe the important role of galactic winds in protogalaxies. The main conclusion is that the faint population of Lyα emitters are indeed the long sought host population of DLAs. Ultra-faint observations of Lyα emission have exceptional potential to directly probe the spatial distribution and kinematics of neutral hydrogen in early galaxies.

We present evidence for redshift quantization in the Lyman -a forest of several QSOs. The Ly -a data are at redshifts z from 1.89 to 3.74, and the theory of redshift quantization proposed by Cocke (1983, 1085) is used to scale the quantization interval (24.15 km s -') to these high redshift. The sealing depends on the deceleration parameter qo, and the quantization is present at a statistical significance of greater than 99% for qo = 1/2. This may be taken as confirming the inflationary model of the early history of the universe. The significance of the quantization is highest at go rs 0.48, and the width of the peak is about 0.03 . The result can also be seen as providing confirmatory evidence for both the theory of the redshift quantization and the above value of qo, but at a significance of only 03 %. The scenario proposed for the relativistic generalization of the theory is that of fermion wavefunctione and quantum operators in a background Riemannian spacetime satisfying Einstein's field equations.

Universiẗat, Diss., 2002--Heidelberg.

University, Diss., 2005--Heidelberg.

L'objet de cette thèse est le spectre de puissance à une dimension du flux transmis dans les forêts Lyman-alpha. Les forêts Lyman-alpha sont un motif d'absorption observé dans les spectres de quasars correspondant à l'absorption de la lumière du quasar par les nuages d'hydrogène le long de la ligne de visée. C'est un outil cosmologique puissant car il sonde des échelles relativement petites de l'ordre de quelques Mpc. Il est aussi sensible à de petits effets non-linéaires tel que celui produit par des neutrinos massifs.Premièrement, nous avons développé deux méthodes indépendantes pour mesurer le spectre de puissance. La première est fondée sur une transformée de Fourier et la seconde sur une fonction de vraisemblance. Les deux méthodes sont indépendantes et ont des incertitudes systématiques différentes. La détermination du niveau de bruit dans les données spectrales a fait l'objet d'un traitement particulier, du fait de son impact significatif sur le spectre de puissance calculé. Nous avons appliqué ces méthodes à 13821 spectres de quasars provenant de la 9e publication de données de l'expérience BOSS sélectionnés à partir d'un échantillon de plus de 60000 spectres sur des critères comme le rapport signal sur bruit et la résolution spectrale. Les deux spectres de puissance mesurés sont en bon accord sur les douze domaines de décalage vers le rouge (<z>=2.2 à <z>=4.4) et sur l'ensemble des échelles (0.001 (km/s)^−1 à 0.02 (km/s)^−1). Nous avons soigneusement déterminé les incertitudes systématiques d'origine instrumentale et méthodologique de notre mesure.Ensuite, nous présentons un ensemble de simulations cosmologiques N-corps incluant de la matière noire, du gaz baryonique et des neutrinos visant à modéliser les régions de basse densité sondées par les forêts Lyman-alpha. Les simulations sont conçues pour répondre aux exigences de précision des données BOSS et eBOSS. Elles comportent 768^3 ou 192^3 particules de chaque type et explorent des volumes allant de (25 Mpc/h)^3 pour les simulations haute résolution à (100 Mpc/h)^3 pour les simulations grand volume. En utilisant une technique de raboutage, nous atteignons une précision équivalente à une simulation comportant 3072^3 particules de chaque type dans un volume de (100 Mpc/h)^3. Nous montrons que cette technique est précise à 2% sur des échelles allant de quelques Mpc jusqu'à quelques dizaines de Mpc. Nous explorons l'effet sur le spectre de puissance de 4 paramètres cosmologiques (n_s, sigma_8, Omega_m ,H_0), 2 paramètres astrophysiques (T_0, gamma) décrivant la relation température/densité du milieu intergalactique et de la somme des masses des neutrinos. En faisant varier ces paramètres autour d'un modèle central choisi en accord avec les résultats de Planck, nous avons construit une grille de simulations, permettant non seulement l'étude de l'effet de chaque paramètre individuellement mais aussi l'effet de chaque paire de paramètres. Nous obtenons ainsi un développement au deuxième ordre complet, incluant les termes croisés, autour de notre modèle central. Nous avons vérifié la validité de ce développement avec des simulations indépendantes obtenues soit avec des paramètres différents soit une graine différente pour la génération des conditions initiales. Une comparaison entre le spectre de puissance mesuré à partir des données dans la première partie et celui obtenu à partir de nos simulations montre un excellent accord.Enfin, même s'il reste des biais potentiels et des erreurs systématiques à étudier dans nos simulations, nous avons réalisé des ajustements en combinant notre mesure du spectre de puissance à d'autres sondes cosmologiques comme les mesures du fond diffus cosmologique par le satellite Planck. Ces résultats préliminaires sont très encourageants car ils mènent à des contraintes sur les paramètres cosmologiques parmi les plus précises à ce jour, en particulier sur la sommes des masses des neutrinos avec une limite supérieure à 0.1 ev. / The framework of the studies presented in this thesis is the one-dimensional power spectrum of the transmitted flux in the Lyman-alpha forests. The Lyman-alpha forest is an an absorption pattern seen in the spectra of high redshift quasars corresponding to the absorption of the quasar light by the hydrogen clouds along the line of sight. It is a powerful cosmological tool as it probes relatively small scales, of the order of a few Mpc. It is also sensible to small non-linear effects such as the one induced by massive neutrinos.First, we have developed two independent methods to measure the one-dimensional power spectrum of the transmitted flux in the Lyman-alpha forest. The first method is based on a Fourier transform, and the second on a maximum likelihood estimator. The two methods are independent and have different systematic uncertainties. The determination of the noise level in the data spectra was subject to a novel treatment, because of its significant impact on the derived power spectrum. We applied the two methods to 13,821 quasar spectra from SDSS-III/BOSS DR9 selected from a larger sample of over 60,000 spectra on the basis of their high quality, large signal-to-noise ratio, and good spectral resolution. The power spectra measured using either approach are in good agreement over all twelve redshift bins from <z>=2.2 to <z>=4.4, and scales from 0.001 (km/s)^−1 to 0.02 (km/s)^−1. We carefully determined the methodological and instrumental systematic uncertainties of our measurements.Then, we present a suite of cosmological N-body simulations with cold dark matter, baryons and neutrinos aiming at modeling the low-density regions of the IGM as probed by the Lyman-alpha forests at high redshift. The simulations are designed to match the requirements imposed by the quality of BOSS and eBOSS data. They are made using either 768^3 or 192^3 particles of each type, spanning volumes ranging from (25 Mpc/h)^3 for high-resolution simulations to (100 Mpc/h)^3 for large-volume ones. Using a splicing technique, the resolution is further enhanced to reach the equivalent of simulations with 3072^3 = 29 billion particles of each type in a (100 Mpc/h)^3 box size, i.e. a mean mass per gas particle of 1.2x10^5 solar masses. We show that the resulting power spectrum is accurate at the 2% level over the full range from a few Mpc to several tens of Mpc. We explore the effect on the one-dimensional transmitted-flux power spectrum of 4 cosmological parameters (n_s, sigma_8, Omega_m ,H_0), 2 astrophysical parameters (T_0, gamma) related to the heating rate of the IGM and the sum of the neutrino masses. By varying the input parameters around a central model chosen to be in agreement with the latest Planck results, we built a grid of simulations that allows the study of the impact on the flux power spectrum of these seven relevant parameters. We improve upon previous studies by not only measuring the effect of each parameter individually, but also probing the impact of the simultaneous variation of each pair of parameters. We thus provide a full second-order expansion, including cross-terms, around our central model. We check the validity of the second-order expansion with independent simulations obtained either with different cosmological parameters or different seeds for the initial condition generation. Finally, a comparison to the one-dimensional Lyman-alpha forest power spectrum obtained in the first part with BOSS data shows an excellent agreement.Eventually, even if there are still some potential biases and systematic errors that need to be studied in our simulation, we performed cosmological fits combining our measurement of the one-dimensional power spectrum and other cosmological probes such as the CMB results provided by Planck. These preliminary results are very encouraging as they lead to some of the tighest cosmological constraints as of today, especially on the sum of the neutrino masses with an upper limit of 0.1 eV.

abstract: Galaxies with strong Lyman-alpha (Lya) emission line (also called Lya galaxies or emitters) offer an unique probe of the epoch of reionization - one of the important phases when most of the neutral hydrogen in the universe was ionized. In addition, Lya galaxies at high redshifts are a powerful tool to study low-mass galaxy formation. Since current observations suggest that the reionization is complete by redshift z~ 6, it is therefore necessary to discover galaxies at z > 6, to use their luminosity function (LF) as a probe of reionization. I found five z = 7.7 candidate Lya galaxies with line fluxes > 7x10-18 erg/s/cm/2 , from three different deep near-infrared (IR) narrowband (NB) imaging surveys in a volume > 4x104Mpc3. From the spectroscopic followup of four candidate galaxies, and with the current spectroscopic sensitivity, the detection of only the brightest candidate galaxy can be ruled out at 5 sigma level. Moreover, these observations successfully demonstrate that the sensitivity necessary for both, the NB imaging as well as the spectroscopic followup of z~ 8 Lya galaxies can be reached with the current instrumentation. While future, more sensitive spectroscopic observations are necessary, the observed Lya LF at z = 7.7 is consistent with z = 6.6 LF, suggesting that the intergalactic medium (IGM) is relatively ionized even at z = 7.7, with neutral fraction xHI&le; 30%. On the theoretical front, while several models of Lya emitters have been developed, the physical nature of Lya emitters is not yet completely known. Moreover, multi-parameter models and their complexities necessitates a simpler model. I have developed a simple, single-parameter model to populate dark mater halos with Lya emitters. The central tenet of this model, different from many of the earlier models, is that the star-formation rate (SFR), and hence the Lya luminosity, is proportional to the mass accretion rate rather than the total halo mass. This simple model is successful in reproducing many observable including LFs, stellar masses, SFRs, and clustering of Lya emitters from z~ 3 to z~ 7. Finally, using this model, I find that the mass accretion, and hence the star-formation in > 30% of Lya emitters at z~ 3 occur through major mergers, and this fraction increases to ~ 50% at z~7. / Dissertation/Thesis / Ph.D. Astrophysics 2011

Les propriétés globales des galaxies montrent une forte évolution du taux de formation stellaire et de la densité de masse stellaire à l'époque de l'assemblage des galaxies précédent le pic de formation stellaire dans l'univers, produite par plusieurs processus physiques concurrents (fusion, accrétion, rétroaction, environnement, ...). Les propriétés morphologiques des galaxies ont aussi fortement évolué à la même époque. Dans cette thèse, j'étudie comment l'évolution des propriétés morphologique est reliée aux propriétés spectrophotométriques des galaxies depuis z ~ 6. Les données spectroscopiques obtenues au sein du VIMOS Ultra Deep Survey (VUDS), un nouveau sondage spectroscopique unique de ~ 10000 galaxies entre redshift z~2 et z~6 qui fournissent un excellent moyen de sonder l'évolution galactique à travers cette époque cosmique. A partir des mes résultats, je conclus que les différentes propriétés morphologiques de galaxies à formation stellaire aux redshifts 2<z<6 montrent qu'il existe plusieurs façons pour les galaxies de se former. La grande diversité de tailles, la fraction importante de super-amas d'étoiles et de gaz très lumineux indiquant des fusions et ceux moins lumineux résultant probablement d'instabilités dans la formation des disques galactiques, avec la prévalence de galaxies irrégulières couvrant un grand domaine de masse stellaire et formation stellaire, pointent ensemble un scénario ou l'assemblage des galaxies procéde de différents méchanismes physiques. La formation des galaxies apparait plus complexe qu'un scénario simple impliquant la formation d'un disque avec de l'accrétion de gaz pourrait le faire croire. / The global properties of galaxies show a strong evolution of the star formation rate and stellar mass density at the epoch of galaxy assembly, driven by several competing physical processes (merging, accretion, feedback, environment,...). The morphological properties of galaxies are also strongly evolving over the same timescales. I investigate how the evolution of the morphological properties is connected to the spectrophotometric properties of galaxies since z~6. The spectroscopic data obtained within the VIMOS Ultra Deep Survey (VUDS), a new unique spectroscopic survey of ~10000 galaxies between redshifts z~2 and z~6 conducted at the ESO-VLT, combined with the available Hubble Space Telescope imaging surveys such as COSMOS or CANDELS provide a great way of probing galactic evolution across this cosmic epoch.From the results that I have obtained, I conclude that the different morphological properties of star-forming galaxies at 2<z<6 show that there are several mechanisms that take part in galaxy formation. The great diversity in galaxy sizes, the high number of bright two clump systems as well as faint multi-clump systems indicating merger and disk instabilities processes, respectively, and the wide range in physical properties that are populated by irregular galaxies all point to a diverse history for galaxy formation. This suggests that forming galaxies is far more complex that the simple explanation of evolution from gas accretion alone.

Angular differential imaging provides a novel way of probing high contrast regions of our universe. Until now, its applications have been primarily localized to searching for exoplanets around nearby stars. This work presents a suite of applications of angular differential imaging from the theoretical underpinning of data reduction, to its use characterizing substellar objects, to a new application looking for the host galaxies of damped Lyman α systems which are usually lost in the glare of ultra-bright quasars along the line of sight. The search for exoplanets utilizes angular differential imaging and relies on complex algorithms to remove residual speckles and artifacts in the images. One such algorithm, the Template Locally Optimized Combination of Images (TLOCI), uses a least-squares method to maximize the signal-to-noise ratio and can be used with variable parameters, such as an input spectral template, matrix inversion method, aggressivity and unsharp mask size. Given the large volume of image sequences that need to be processed in any exoplanet survey, it is important to find a small set of parameters that can maximize detections for any conditions. Rigorous testing of these parameters were done with on-sky images and simulated inserted planets to find the optimal combination of parameters. Overall, a standard matrix inversion, along with two to three input templates, a modest aggressivity of 0.7 and the smallest unsharp mask was found to be the best choice to balance optimal detection. Beyond optimizations, TLOCI has been used in conjunction with angular differential imaging to characterize substellar objects in our local solar neighbourhood. In particular, the star HD 984 was imaged as a part of the Gemini Planet Imager Exoplanet Survey. Although previously known to have a substellar companion, new imaging presented here in the H and J bands help further characterize this object. Comparisons with a library of brown dwarf spectral types found a best match to HD 984 B of a type M7±2. Orbital fitting suggests an 18 AU (70 year) orbit, with a 68% confidence interval between 12 and 27 AU. Object magnitude was used to find the luminosity, mass and temperature using DUSTY models. Although angular differential imaging has proven its value in high contrast imaging, it has largely remained in the field of substellar object detection, despite other high contrast regimes in which it could be applied. One potential application is outside the local solar neighbourhood with studies of damped Lyman α systems, which have struggled to identify host galaxies thought to be caused by systems seen in the spectra of bright quasars. Work herein presents the first application of angular differential imaging to finding the host galaxies to damped Lyman α systems. Using ADI we identified three potential systems within 30kpc of the sightline of the quasar and demonstrate the potential for future imaging of galaxies at close separations. In summary, this thesis presents a comprehensive look at multiple aspects of high contrast angular differential imaging. It explores optimizations with a data reduction algorithm, implementations characterizing substellar objects, and new applications imaging galaxies. / Graduate