We describe the execution and data reduction of the European Southern Observatory Large Programme "Quasars and their absorption lines: a legacy survey of the high-redshift Universe with VLT/X-shooter" (hereafter "XQ-100"). XQ-100 has produced and made publicly available a homogeneous and high-quality sample of echelle spectra of 100 quasars (QSOs) at redshifts z similar or equal to 3.5-4.5 observed with full spectral coverage from 315 to 2500 nm at a resolving power ranging from R similar to 4000 to 7000, depending on wavelength. The median signal-to-noise ratios are 33, 25 and 43, as measured at rest-frame wavelengths 1700, 3000 and 3600 angstrom, respectively. This paper provides future users of XQ-100 data with the basic statistics of the survey, along with details of target selection, data acquisition and data reduction. The paper accompanies the public release of all data products, including 100 reduced spectra. XQ-100 is the largest spectroscopic survey to date of high-redshift QSOs with simultaneous rest-frame UV/optical coverage, and as such enables a wide range of extragalactic research, from cosmology and galaxy evolution to AGN astrophysics.

Precision cosmology challenges many aspects of fundamental physics. In particular, quasar absorption lines test the assumed constancy of fundamental constants over cosmological time-scales and distances. Until recently, the most reliable technique was the alkali doublet (AD) method where the measured doublet separation probes variations in the fine-structure constant, ???? e2/??c. However, the recently introduced many-multiplet (MM) method provides several advantages, including a demonstrated ???10-fold precision gain. This thesis presents detailed MM analyses of 3 independent Keck/HIRES samples containing 128 absorption systems with 0.2 &gt zabs &gt 3.7. We find 5.6 ?? statistical evidence for a smaller ?? in the absorption clouds: ????/?? = (-0.574 ?? 0.102) x 10-5. All three samples separately yield consistent, significant ????/??. The data marginally prefer constant d??/dt rather than constant ????/??. The two-point correlation function for ?? and the angular distribution of ????/?? give no evidence for spatial variations. We also analyse 21 Keck/HIRES Si iv doublets, obtaining a 3-fold relative precision gain over previous AD studies: ????/?? = (-0.5 ?? 1.3) x 10-5 for 2.0 &gt zabs &gt 3.1. Our statistical evidence for varying ?? requires careful consideration of systematic errors. Modelling demonstrates that atmospheric dispersion is potentially important. However, the quasar spectra suggest a negligible effect on ????/??. Cosmological variation in Mg isotopic abundances may affect ????/?? at zabs &gt 1.8. Galactic observations and theory suggest diminished 25;26Mg abundances in the low metallicity quasar absorbers. Removing 25;26Mg isotopes yields more negative ????/?? values. Overall, known systematic errors can not explain our results. We also constrain variations in y ?? ?? 2gp, comparing H i 21-cm and millimetrewave molecular absorption in 2 systems. Fitting both the H i and molecular lines yields the tightest, most reliable current constraints: ??y/y = (-0.20??0.44)x10-5 and (-0.16??0.54)x10-5 at zabs = 0.2467 and 0.6847 respectively. Possible line-ofsight velocity differences between the H i and molecular absorbing regions dominate these 1 ?? errors. A larger sample of mm/H i comparisons is required to reliably quantify this uncertainty and provide a potentially crucial check on the MM result.

Ce travail consiste en létude de deux échantillons de quasars lumineux et proches. Tout dabord, nous effectuons une étude simultanée de données provenant du Hubble Space Telescope et du Very Large Telescope dans le but détudier dans le détail les caractéristiques des galaxies hôtes de 6 quasars. Un traitement adéquat des données spectrales du VLT et des images du HST, basé sur la méthode de déconvolution MCS, permet de décrire avec une grande précision la structure de la galaxie hôte ainsi que diverses propriétés du système. Ainsi, nous pouvons caractériser linfluence du quasar sur son environnement. Nos analyses prouvent en effet la présence de gaz ionisé par le quasar dans des régions éloignées du centre et apparemment dépourvues détoiles, mais aussi lexistence de zones galactiques réfléchissant le rayonnement du quasar via des électrons libres ou de la poussière. La dynamique du gaz entourant le quasar est analysée via la courbe de rotation du système. Nos méthodes permettent également de résoudre les régions centrales (< 1 kpc) des galaxies hôtes et den analyser le contenu. Suite à ce projet, une étude dun plus grand échantillon de 104 quasars de bas redshift a été menée. Les résultats obtenus pour un sous échantillon de 69 quasars (observé avec le NTT/SUSI2 et complété par des données darchives), formant lessentiel de la seconde partie du travail, peuvent se résumer comme suit : La magnitude absolue du quasar ne se corrèle pas fortement avec celle de la galaxie hôte sur lensemble de léchantillon. Cependant, la corrélation est plus robuste si lon ne considère que les galaxies elliptiques. La proportion de galaxies arborant des traces dinteractions gravitationnelles (' 60%) est assez élevée, mais cela ne permet pas de déterminer univoquement si elles influencent lactivation du quasar. Les hôtes possèdent en moyenne une plus grande quantité de gaz ionisé par rapport aux galaxies inactives. Cette tendance est encore plus forte pour les elliptiques, qui pourtant ne contiennent quune faible quantité de gaz lorsquelle sont inactives. Les galaxies hôtes les plus asymétriques, associées à des collisions galactiques majeures, contiennent également plus de gaz ionisé que les moins asymétriques. Quelques elliptiques de léchantillon possèdent un noyau actif décentré par rapport au centre de leur galaxie. Ce décentrage suggère une collision galactique importante, voire même une éjection du trou noir avec son disque daccrétion à partir de la fusion dun système binaire de trous noirs. Quelques cas particuliers, méritant dêtre observés à plus haute résolution spatiale et en spectro-3D, sont décrits pour la première fois. La thèse se compose des deux articles liés aux études résumées ci-dessus. Le premier, publié dans lAstrophysical Journal en juin 2008 (Letawe et al. [72]), traite des images HST et des spectres VLT, et le second, soumis au Monthly Notices of the Royal Astronomical Society en septembre 2009, contient lanalyse de léchantillon SUSI2. Ces articles sont complétés par des contextualisations et analyses supplémentaires non publiées. This work consists in the study of two samples of nearby luminous quasars. First of all,we compare quasar images obtained from the Hubble Space Telescope and slit spectra from the VLT/FORS1 in order to study the properties of six quasar host galaxies. An appropriate data processing, based on the MCS deconvolution method, allows to separate the central source from the host and to describe their content in detail. We are able to characterize the quasars influence on its surrounding. Indeed, our analysis proves the presence of gas ionized by the quasar in remote regions apparently devoid of stars, but also the presence of quasar emission lines reflected by free electrons or dust. The dynamics of the gas surrounding the quasar is revealed via rotation curves and information about the central regions (< 1 kpc) is accessible thanks to our powerful quasar-host separation methods. As a second part, a study of a larger sample of 104 nearby quasars is made. Results for a subsample of 69 quasars (observed with NTT/SUSI2 and completed with archive data) form the second part of this work. They can be summarized as follows : The quasars absolute magnitude does not correlate strongly with the host magnitude. However, this correlation becomes more robust if we consider only elliptical hosts. The proportion of galaxies showing signs of gravitational interactions is quite large (' 60%), but this does not allow to assess unequivocally their influence in the triggering of the quasar activity. There is a tendency for quasar hosts to contain more ionized gas than in inactive galaxies. This trend is even stronger for ellipticals, which, when inactive, do not usually contain much gas. The most asymmetric hosts, linked to strong merging processes, also tend to have more ionized gas than less asymmetric ones. A few ellipticals have their active nucleus shifted compared to the galactic center. Such ff-nuclear activity is suggestive of important galactic collisions, and may be due to a gravitational black hole recoil in the fusion of binary black holes system. A few peculiar cases, deserving higher resolution imaging or 3D-spectroscopy, are described here for the first time. The thesis is composed of two articles linked to the two studies summarized above. The first one, published in the Astrophysical Journal in June 2008 (Letawe et al. [72]), deals with HST and VLT data. The second one, submitted to the Monthly Notices of the Royal Astronomical Society in September 2009, contains the analysis of the SUSI2 sample. These articles are completed by introductions and unplublished supplementary analyses and results.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 282-294). Available also in a digital version from Dissertation Abstracts.

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The goal of this thesis is to develop an obscured AGN model for the X-ray background (XRB), and then to test the model via its predictions for the intensity of the cosmic background in the far infra-red, and by searching for obscured nuclei in individual X-ray sources in the near infra-red. A model invoking populations of obscured QSOs with a flat distribution of absorbing columns is found to give a good fit to the X-ray source counts and to the XRB spectrum. The model also accommodates the recent detection of a population of narrow-line X-ray galaxies, identifying them as low-luminosity obscured AGN. We investigate the selection effects present in optical QSO samples, and find that absorption in both the X-ray and optical wavebands combine to produce the tight observed X-ray/optical correlation, while still allowing a wide range of intrinsic column densities. X-ray sources with no obvious optical counterparts are predicted by this model, with a frequency in agreement with the numbers of these 'blank field' sources found in deep ROSAT surveys. We predict that in forthcoming AXAF surveys, ~ 50 per cent of the sources detected will be optically blank and lie at z (^>))(_~) 1. Obscured QSOs are estimated to outnumber unobscured QSOs by a factor of at least four to one. At longer wavelengths, we make a conservative prediction that obscured QSOs can account for approximately ten per cent of the sub-mm number counts and the far infra-red background, which is a modest, but non-negligible fraction. We then make observations to determine the extent of dust reddening in X-ray galaxies and QSOs, in the light of predictions of our obscured QSO model. We present K-band imaging of ROSAT and ASCA X-ray luminous galaxies and blank field sources. A trend is observed between the hardness of the X-ray spectra and the occurrence of red, unresolved counterparts, consistent with an obscured QSO origin for the X-ray emission. Near infra-red spectroscopy of X-ray luminous galaxies is then presented, searching for broad Pa(_a) emission lines. A broad line is possibly detected in one of six galaxies observed, which would indicate AGN activity. From far infra-red ISO photometry of X-ray galaxies and QSOs, we detect emission at ~ lOOμm from six narrow- line galaxies at low redshift, and from a Type 2 QSO at higher redshift. For at least two of the low redshift galaxies, there is clear proof of AGN activity on the grounds of X-ray variability and near infra-red spectroscopy. This, together with the 100μm detections, forms conclusive proof of the presence of dust-enshrouded AGN in at least some X-ray galaxies, supporting the obscured QSO explanation for the cosmic X-ray background.

Precision cosmology challenges many aspects of fundamental physics. In particular, quasar absorption lines test the assumed constancy of fundamental constants over cosmological time-scales and distances. Until recently, the most reliable technique was the alkali doublet (AD) method where the measured doublet separation probes variations in the fine-structure constant, ???? e2/??c. However, the recently introduced many-multiplet (MM) method provides several advantages, including a demonstrated ???10-fold precision gain. This thesis presents detailed MM analyses of 3 independent Keck/HIRES samples containing 128 absorption systems with 0.2 &gt zabs &gt 3.7. We find 5.6 ?? statistical evidence for a smaller ?? in the absorption clouds: ????/?? = (-0.574 ?? 0.102) x 10-5. All three samples separately yield consistent, significant ????/??. The data marginally prefer constant d??/dt rather than constant ????/??. The two-point correlation function for ?? and the angular distribution of ????/?? give no evidence for spatial variations. We also analyse 21 Keck/HIRES Si iv doublets, obtaining a 3-fold relative precision gain over previous AD studies: ????/?? = (-0.5 ?? 1.3) x 10-5 for 2.0 &gt zabs &gt 3.1. Our statistical evidence for varying ?? requires careful consideration of systematic errors. Modelling demonstrates that atmospheric dispersion is potentially important. However, the quasar spectra suggest a negligible effect on ????/??. Cosmological variation in Mg isotopic abundances may affect ????/?? at zabs &gt 1.8. Galactic observations and theory suggest diminished 25;26Mg abundances in the low metallicity quasar absorbers. Removing 25;26Mg isotopes yields more negative ????/?? values. Overall, known systematic errors can not explain our results. We also constrain variations in y ?? ?? 2gp, comparing H i 21-cm and millimetrewave molecular absorption in 2 systems. Fitting both the H i and molecular lines yields the tightest, most reliable current constraints: ??y/y = (-0.20??0.44)x10-5 and (-0.16??0.54)x10-5 at zabs = 0.2467 and 0.6847 respectively. Possible line-ofsight velocity differences between the H i and molecular absorbing regions dominate these 1 ?? errors. A larger sample of mm/H i comparisons is required to reliably quantify this uncertainty and provide a potentially crucial check on the MM result.

Thesis (Ph. D.)--University of New South Wales, 2000. / Also available online.

Thesis (Ph. D.)--University of New South Wales, 2002. / Also available online.