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In this thesis, we exploit the potential of existing QSO and galaxy surveys for investigating the nature of the large scale structure in the Universe. A detailed analysis of clustering and redshift- space distortions allows us to constrain cosmological parameters. We model the anisotropies due to dynamical and geometrical effects in the measured clustering pattern of distant QSOs from the 2dF QSO Survey (2QZ) and also Lyman break galaxies. The 2QZ is then combined with the QSO sample from the 2dF SDSS LRG and QSO Survey (2SLAQ) to study the luminosity dependence of QSO clustering. Using AT-body simulations, we estimate the statistical gains in the determination of cosmological parameters from future LRG surveys. We measure the clustering of distant QSOs from the 2QZ survey by performing a correlation analysis of redshift-space (z-space) distortions. To interpret the z-space correlation function measured in orthogonal directions, ع(σ,π)， we require an accurate model for the QSO real-space correlation function, ع (r). Motivated by the form for ع (r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard ACDM predictions, we use a double power-law model for ع (r). which gives a good fit to the z-space and projected correlation functions. By fitting functional forms of ع(σ,π) which include both dynamical and geometrical modelling, we find, as expected, that β (which parameterises the infall into overdense regions) and the density of the Universe (Ω(^0_M)) are degenerate. However, this degeneracy can be lifted by using linear theory predictions under different cosmological scenarios. Using the 2QZ survey, we obtain: βQAO (z=1.4) = 0.50 (^0.13_0.15), Ω(^0_M) = 0.35 (^+0.19_-0.13). The modelling of geometrical and dynamical anisotropies in the measured ع(σ,π) pattern is then applied to a sample of distant Lymari-break galaxies. The presence of feedback mechanisms in these z〜 3 star-forming galaxies heightens the importance of understanding the effects of z-space distortions. Despite the limited size of the fields, which hampers the determination of ع(r) at large scales, we find that a double-power law ع(s) parameterisation is consistent with the correlation function measurements. This double power law model is then used as an input for the ع(σ,π) fitting and subsequent constraining of cosmological parameters. This investigation reveals that: ßLBG (z= 3) = 0.25± (^+0.05_-0.05) and Ω(^0_M) = 0.55(^+0.45_-0.16). The combination of the 2QZ with the fainter 2SLAQ QSO sample reveals that QSO clustering does not depend strongly on luminosity. This result is consistent with models which predict that haloes of similar mass can harbour QSOs of different luminosities. By assuming ellipsoidal models for the collapse of density perturbations, we test this hypothesis and estimate the mass of the dark matter haloes which the QSOs inhabit. We find that halo mass does not seem to evolve strongly with redshift nor depend on QSO luminosity. Having determined the black hole mass associated with the QSOs, we investigate how it correlates with luminosity and redshift and ascertain the relation between Eddington efficiency and black hole mass. Our results suggest that: (i) black hole mass does not depend strongly on accretion efficiency and (іі) black holes associated with QSOs of different luminosities have similar masses. Finally, the Hubble Volume simulation is used to construct a mock sample of a future ΑΑΩ Luminous Red Galaxy (LRG) survey. The ultimate aims of this survey are to identify the baryon acoustic features in the LRG clustering signal and to determine the equation of state of dark energy. We apply the z-space distortion analysis developed previously in the thesis to infer the statistical gain in terms of determinations of ß(_LRG) (z~ 0.7) and Ω(+0_m) .This thesis exploits the wealth of information contained in cosmological surveys, and demonstrates how the use of tools such as clustering statistics or z-space distortion analyses permit the extraction of such information.

This Thesis presents a study of galaxies and quasars from the viewpoint of their optical, infrared and X-ray properties by combining optical data from Gemini and WIYN with near to far-IR and optical data from the SWIRE survey and X-ray data from Chandra. This work represents the largest existing optical spectroscopic survey in ELAIS-N1 with ∽300 reliable spectroscopic redshifts and the largest Xray survey, in the same field, which has extended the previous X-ray coverage in ELAIS-N1 by a factor of 12 and has detected more than 600 X-ray sources. Optical spectroscopy is used both to calibrate photometric redshift techniques and distinguish between star forming galaxies and quasars. The merged X-ray, optical and infrared catalogue is used to determine spectral energy distributions and correctly identify and characterize AGN, star forming galaxies and the link between black hole growth and star formation in the host galaxy.

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.