Дисертації з теми "Quasars : absorption"

The origin of Broad Absorption Line Quasars (BAL QSOs) is still an open issue. Accounting for ~20% of the QSO population, these objects present broad absorption lines in their optical spectra generated from outflows with velocities up to 0.2 c. Nowadays, the hypotheses about their nature are principally related to orientation or evolutionary scenarios. In the first one, absorption lines are produced by outflows originated by the accretion disk, basically present in all QSOs, but seen only when they intercept the line of sight. In the second hypothesis, BAL QSOs would be young or recently re-fueled QSOs, still ejecting their dust cocoon. In this case orientation would not play a role, since the absorption features would be produced by spherically ejected matter. In this work we present the results of a multi-frequency study of a Radio-Loud BAL QSO sample, and a comparison sample of Radio-Loud non-BAL QSOs. We performed observations from radio to Near-Infrared, aiming at collecting useful informations about the orientation, the age, and the morphologies of these objects. Various techniques have been applied, including local and continental radio interferometry, single dish observations and spectroscopy. The comparison with the non-BAL QSO sample allows us to conclude that no particular orientation is present in BAL QSOs. Moreover, various morphologies and ages can be found, analogously to "normal" QSOs. Thus, the solution to this astrophysical problem seems not to reside in a peculiarity of the BAL QSO subclass with respect to non-BAL QSOs, since both the studied models do not completely explain the observed characteristics. Further experiments with future instrumentation will allow us to underline useful differences and test the physical conditions in BAL QSOs.

The origin of Broad Absorption Line Quasars (BAL QSOs) is still an open issue. Accounting for ~20% of the QSO population, these objects present broad absorption lines in their optical spectra generated from outflows with velocities up to 0.2 c. Nowadays, the hypotheses about their nature are principally related to orientation or evolutionary scenarios. In the first one, absorption lines are produced by outflows originated by the accretion disk, basically present in all QSOs, but seen only when they intercept the line of sight. In the second hypothesis, BAL QSOs would be young or recently re-fueled QSOs, still ejecting their dust cocoon. In this case orientation would not play a role, since the absorption features would be produced by spherically ejected matter. In this work we present the results of a multi-frequency study of a Radio-Loud BAL QSO sample, and a comparison sample of Radio-Loud non-BAL QSOs. We performed observations from radio to Near-Infrared, aiming at collecting useful informations about the orientation, the age, and the morphologies of these objects. Various techniques have been applied, including local and continental radio interferometry, single dish observations and spectroscopy. The comparison with the non-BAL QSO sample allows us to conclude that no particular orientation is present in BAL QSOs. Moreover, various morphologies and ages can be found, analogously to "normal" QSOs. Thus, the solution to this astrophysical problem seems not to reside in a peculiarity of the BAL QSO subclass with respect to non-BAL QSOs, since both the studied models do not completely explain the observed characteristics. Further experiments with future instrumentation will allow us to underline useful differences and test the physical conditions in BAL QSOs.

This dissertation investigates the properties of the metal-containing absorption lines seen in quasar spectra which have Z(abs) < < Z(em). These systems, which probably originate in the halos of galaxies at high redshift, are then compared to observations of the halo and interstellar medium of the Milky Way. We obtained echelle spectra at the Multiple Mirror Telescope (MMT) of the Z = 1.79 absorption system of the quasar B2 1225+317. The velocity profiles showed complex structure which varied from ion to ion, with ionization and column densities varying from component to component. The relative colums were consistent with the expectations for approximately interstellar abundance, low density material, in equilibrium with the ultraviolet radiation field of a spiral galaxy for λ > 912 A, and the integrated light from QSOs at Z = 1.79 for λ < 912 A. The aggregate C IV profile has a width of about 450 km/sec, larger than that expected for a single galaxy halo, however. With the MMT spectrograph and echellette grating, and MMT echelle, we studied the properties of three other redshift systems of B2 1225+317, which are optically thin at the Lyman limit, but have saturated Lyman alpha, and unlike material in the Milky Way, have strong C IV and no detectable C II. In some cases Si III and Si IV are weakly detected. Constructing photoionization models, we derive low total densities, cloud diameters on the order of a few kiloparsecs, and abundances which are consistent with the interstellar values. We calculated the contribution of quasars to the UV radiation field as a function of redshift. The calculated field depends on a number of uncertain assumptions, which were varied in order to estimate their effect on the result. Finally, we discuss an important input into these calculations, the continuum spectral energy distribution for quasars, with particular attention to the extreme ultraviolet.

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 > zabs > 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 > zabs > 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 > 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.

Very few low-ionization broad absorption line (LoBAL) QSOs have been found at high redshifts, to date. One high-redshift LoBAL QSO, J0122+1216, was recently discovered by the Lijiang 2.4 m Telescope, with an initial redshift determination of 4.76. Aiming to investigate its physical properties, we carried out follow-up observations in the optical and near-IR spectroscopy. Near-IR spectra from UKIRT and P200 confirm that it is a LoBAL, with a new redshift determination of 4.82 +/- 0.01 based on the Mg II emission-line. The new Mg II redshift determination reveals strong blueshifts and asymmetry of the high-ionization emission lines. We estimate a black hole mass of similar to 2.3 x 10(9) M-circle dot and Eddington ratio of similar to 1.0 according to the empirical Mg II-based single-epoch relation and bolometric correction factor. It is possible that strong outflows are the result of an extreme quasar environment driven by the high Eddington ratio. A lower limit on the outflowing kinetic power (>0.9% L-Edd) is derived from both emission and absorption lines, indicating that these outflows play a significant role in the feedback process that regulates the growth of its black hole, as well as host galaxy evolution.

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

SDSS J163459.82+204936.0 is a local (z = 0.1293) infrared-luminous quasar with L-IR = 10(11.91) L-circle dot. We present a detailed multiwavelength study of both the host galaxy and the nucleus. The host galaxy, appearing as an early-type galaxy in the optical images and spectra, demonstrates violent, obscured star formation activities with SFR approximate to 140 M-circle dot yr(-1), estimated from either the polycyclic aromatic hydrocarbon emission or IR luminosity. The optical to NIR spectra exhibit a blueshifted narrow cuspy component in H beta, He I lambda lambda 5876, 10830, and other emission lines consistently with an offset velocity of approximate to 900 km s(-1), as well as additional blueshifting phenomena in high-ionization lines (e.g., a blueshifted broad component of He I lambda 10830 and the bulk blueshifting of [O III].5007), while there exist blueshifted broad absorption lines (BALs) in Na I. D and He I lambda lambda 3889, 10830, indicative of the active galactic nucleus outflows producing BALs and emission lines. Constrained mutually by the several BALs in the photoionization simulations with Cloudy, the physical properties of the absorption line outflow are derived as follows: density 10(4) < n(H) less than or similar to 10(5) cm(-3), ionization parameter 10(-1.3) less than or similar to U 10(-0.7), and column density 10(22.5) less than or similar to N-H less than or similar to 10(22.9) cm(-2), which are similar to those derived for the emission line outflows. This similarity suggests a common origin. Taking advantages of both the absorption lines and outflowing emission lines, we find that the outflow gas is located at a distance of similar to 48-65 pc from the nucleus and that the kinetic luminosity of the outflow is 10(44)-10(46) erg s(-1). J1634+2049 has a off-centered galactic ring on the scale of similar to 30. kpc that is proved to be formed by a recent head-on collision by a nearby galaxy for which we spectroscopically measure the redshift. Thus, this quasar is a valuable object in the transitional phase emerging out of dust enshrouding as depicted by the coevolution scenario invoking galaxy merger (or violent interaction) and quasar feedback. Its proximity enables our further observational investigations in detail (or tests) of the co-evolution paradigm.

Le Milieu Circumgalactique (CGM) désigne la zone située autour des galaxies qui constitue l’interface entre celles-ci et le milieu intergalactique. Le gaz qu’il contient provient notamment de phénomènes d’accrétion permettant d’alimenter la formation d’étoiles sur de longues périodes, et d’éjections provenant de l’explosion de supernovæ et causant des vents galactiques. Aujourd’hui le CGM constitue un test pour les modèles théoriques et les simulations qui ne parviennent pas encore à reproduire l’ensemble de ses caractéristiques physiques. Du point de vue observationnel, son étude est rendue compliquée par son aspect multi-phase et sa faible densité. Celle-ci implique une faible brillance de surface qui le rend presque invisible en émission avec les instruments actuels. C’est pourquoi il est, la plupart du temps, étudié en absorption, notamment grace à des lignes de visée de quasars. Dans cette thèse nous avons tenté d’améliorer la connaissance de la phase tiède du CGM (T~10^4K) en nous basant sur le doublet d’absorption à 2796,2803A du MgII. Pour cela nous avons utilisé l’échantillon MEGAFLOW qui se compose de 22 champs de quasars observés avec le spectrographe intégral de champs MUSE et le spectrographe haute résolution UVES. Le large champ de vue de MUSE et sa grande sensibilité le rendent idéal pour détecter les galaxies causant les absorptions. Cet échantillon, parmi les plus larges disponibles actuellement, est particulièrement adapté à l’étude du CGM des galaxies actives à redshift 0.4< z <1.5. Dans un premier temps nous nous sommes intéressés aux galaxies isolées, car celles-ci peuvent être associées sans ambiguïté aux absorptions MgII observées. Nous avons mesuré leur profil d’absorption en fonction du paramètre d’impact et étudié sa dépendance à différentes propriétés (masses stellaires, taux de formation d’étoiles et redshift). Dans un second temps nous avons conduit une analyse similaire pour les groupes de galaxies en les identifiant à l’aveugle grâce à une méthode combinant deux algorithmes de détection. Nous constatons d’abord que les absorptions de MgII sont principalement causées par des petits ensembles de galaxies (1 à 3) compatibles avec la corrélation naturelle et non par des groupes. La sélection rigoureuse des galaxies isolées permet d’obtenir une faible dispersion autour du profil d’absorption. Celui-ci s’étend sensiblement plus loin que ceux prédit par les simulations actuelles. Il semble en particulier que toutes les galaxies ayant une masse >10^9 Msun présentent une absorption >0.1A dans un paramètre d’impact de 50 kpc. Nous observons également que l’étendue des absorptions MgII est significativement plus importante le long du petit axe que le long du grand axe ce qui indique le rôle prépondérant des vents sur le CGM. D’autre part, Les halos de MgII s’étendent beaucoup plus loin pour les groupes que pour les galaxies isolées, et ce, même pour des masses de halos similaires et quelque soit la définition du paramètre d’impact utilisé. Cela témoigne des mécanismes différents pour ces deux environnements. L’intensité et la probabilité des absorptions MgII est positivement corrélée au SFR et à la masse stellaire. Elles ont également tendance à stagner ou diminuer avec le temps cosmique ce qui indique que la phase tiède ne croit pas comme les halos de matière noire. Nos observations favorisent plutôt le scénario de halos de gaz qui suivent la baisse du SFR cosmique. Enfin nous avons exploré de possibles liens entre les propriétés des halos de matière noire et les absorptions traçant la phase tiède. Nous pensons que le travail présenté ici mériterait d’être prolongé sur d’autres populations de galaxies et d’être comparé à des simulations afin de mieux contraindre les processus gouvernant l’évolution des galaxies
The Circumgalactic Medium (CGM) refers to the area surrounding galaxies that constitutes the interface between them and the intergalactic medium. The gas it contains originates, in particular, from accretion mechanisms which fuel star formation over long periods, and from ejections caused by supernova explosions that create galactic winds. Today, the CGM presents a test for theoretical models and simulations, which have not yet succeeded in reproducing all of its physical characteristics. Observationally, studying the CGM is challenging because of its multi-phase nature and low density. It’s low surface brightness, makes it almost invisible in emission with current instruments. Therefore, it is mostly studied in absorption, particularly through quasar sightlines. In this thesis, we aimed to improve the understanding of the warm phase of the CGM (T~10^4K) traced by the 2796,2803 Å MgII absorption doublet. To this end, we used the MEGAFLOW sample, consisting of 22 quasar fields observed with the integral field spectrograph MUSE and the high-resolution spectrograph UVES. The wide field of view and high sensitivity of MUSE make it ideal for detecting galaxies causing the absorptions. This sample, one of the largest currently available, is particularly suited for studying the CGM of active galaxies at redshift 0.4 < z < 1.5. First, we focused on isolated galaxies because they can be unambiguously associated with the observed MgII absorptions. We measured their absorption profiles as a function of impact parameter and studied its dependence on various properties (stellar masses, star formation rates, and redshift). Subsequently, we conducted a similar analysis for galaxy groups, identifying them blindly using a method combining two detection algorithms. We find that MgII absorptions are primarily caused by small ensembles of galaxies (1 to 3) compatible with natural correlation and not by groups. The rigorous selection of isolated galaxies results in a low dispersion around the absorption profile, which extends significantly further than those predicted by current simulations. In particular, all galaxies with masses >10^9 Msun exhibit absorption >0.1 Å within an impact parameter of 50 kpc. We find that the extent of MgII absorptions is significantly higher along the minor axis than along the major axis, indicating the predominant role of winds on the CGM. We also observe that MgII halos extend much further for groups than for isolated galaxies, even for similar halo masses and regardless of the impact parameter definition used. This indicates different mechanisms at play in these two environments. The intensity and probability of MgII absorptions are positively correlated with SFR and stellar mass. They also tend to stagnate or decrease with cosmic time, indicating that the warm phase does not grow like dark matter halos. Our observations favor a scenario where gas halos follow the decline of the cosmic SFR. Finally, we explored possible links between dark matter halo properties and absorptions tracing the warm phase. We believe that the work presented here deserves to be extended to other galaxy populations and compared to simulations to better constrain the processes governing galaxy evolution

We present a survey of 72 Seyfert galaxies and quasars observed by the Far Ultraviolet Spectroscopic Explorer (FUSE). Our survey is the largest to date searching for intrinsic UV absorption with high spectral resolution, and is the first step toward a more comprehensive study of intrinsic absorption in low-redshift AGN. We have determined that 72 of 253 available active galactic nuclei (AGN) are viable targets for detection of intrinsic absorption lines. We examined these spectra for signs of intrinsic absorption in the O VI doublet (lambda lamdba 1031.9, 1037.6) and Lyman beta (lambda 1025.7). The fraction of Seyfert 1 galaxies and low-redshift quasars at z<0.15 that show evidence of intrinsic UV absorption is ~50, which is slightly lower than Crenshaw et al. found (60%) based on a smaller sample of C IV absorption in Seyfert 1 galaxies observed with the Hubble Space Telescope (HST). The intrinsic absorption lines are mostly blueshifted with respect to the rest frame of the galaxy, indicating outflow of ionized gas from the AGN. With this new fraction we find a global covering factor of the absorbing gas with respect to the central nucleus of ~0.4. We also provide a deeper analysis of the intrinsic absorption features we found in 35 objects. We have characterized the relation between luminosity and velocity, and examined the relationships between equivalent width, full width at half maximum, velocity and continuum flux. The luminosity/velocity correlation has been explored previously by Laor & Brandt (2002), but at a significantly higher redshift and heavily weighted by Broad Absorption Line quasars. Our survey is for lower redshift and lower luminosity objects, mostly Seyfert galaxies. We have also explored each object with multiple observations for variablity in each of the aforementioned quantities and characterized the variation of equivalent width with continuum flux. Variability for low-z AGN has been seen in the past. In our survey, we find that variability of O VI (lambda lambda 1032, 1038) is less common than for the UV doublets of C IV and N V seen at longer wavelengths, because the O VI absorption is usually saturated. Lyman beta absorption variability is more frequent. In the target-by-target examination we find that Broad Absorption Line (BAL) features and Narrow Absorption Line (NAL) features are related, in that they follow a single relationship between the maximum outflow velocity and the AGN luminosity, and both can be exhibited in similar luminosity objects. IRAS F22456-5125 is one particular Seyfert galaxy that we have selected for modelling due to its interesting assortment of intrinsic absorption lines. It shows a system of five individual kinematic components of absorption features in both O VI lines and in several of the Lyman series lines. We find that each of the components are relatively simple to model and appear to be weak in the X-ray.

We present the first results from an ongoing survey to characterize the circumgalactic medium (CGM) of massive high-redshift galaxies detected as submillimeter galaxies (SMGs). We constructed a parent sample of 163 SMGQSO pairs with separations less than similar to 36" by cross-matching far-infrared-selected galaxies from Herschel with spectroscopically confirmed QSOs. The Herschel sources were selected to match the properties of the SMGs. We determined the sub-arcsecond positions of six Herschel sources with the Very Large Array and obtained secure redshift identification for three of those with near-infrared spectroscopy. The QSO sightlines probe transverse proper distances of 112, 157, and 198. kpc at foreground redshifts of 2.043, 2.515, and 2.184, respectively, which are comparable to the virial radius of the similar to 10(13) M circle dot halos expected to host SMGs. High-quality absorption-line spectroscopy of the QSOs reveals systematically strong H I Ly alpha absorption around all three SMGs, with rest-frame equivalent widths of similar to 2-3 A. However, none of the three absorbers exhibit compelling evidence for optically thick H I gas or metal absorption, in contrast to the dominance of strong neutral absorbers in the CGM of luminous z similar to 2 QSOs. The low covering factor of optically thick H I gas around SMGs tentatively indicates that SMGs may not have as prominent cool gas reservoirs in their halos as the coeval QSOs and that they may inhabit less massive halos than previously thought.

Previous studies have shown that the incidence rate of intervening strong Mg II absorbers towards gamma-ray bursts (GRBs) were a factor of 2-4 higher than towards quasars. Exploring the similar sized and uniformly selected legacy data sets XQ-100 and XSGRB, each consisting of 100 quasar and 81 GRB afterglow spectra obtained with a single instrument (VLT/X-shooter), we demonstrate that there is no disagreement in the number density of strong Mg II absorbers with rest-frame equivalent widths W-r(lambda 2796) > 1 angstrom towards GRBs and quasars in the redshift range 0.1 less than or similar to z less than or similar to 5. With large and similar sample sizes, and path length coverages of Delta z = 57.8 and 254 : 4 for GRBs and quasars, respectively, the incidences of intervening absorbers are consistent within 1 sigma uncertainty levels at all redshifts. For absorbers at z < 2.3, the incidence towards GRBs is a factor of 1.5 +/- 0.4 higher than the expected number of strong Mg II absorbers in Sloan Digital Sky Survey (SDSS) quasar spectra, while for quasar absorbers observed with X-shooter we find an excess factor of 1.4 +/- 0.2 relative to SDSS quasars. Conversely, the incidence rates agree at all redshifts with reported high-spectral-resolution quasar data, and no excess is found. The only remaining discrepancy in incidences is between SDSS Mg II catalogues and high-spectral-resolution studies. The rest-frame equivalent-width distribution also agrees to within 1 sigma uncertainty levels between the GRB and quasar samples. Intervening strong Mg II absorbers towards GRBs are therefore neither unusually frequent, nor unusually strong.

Les raies en absorption observees dans les spectres des quasars permettent de detecter des nuages de gaz dont les densites de surface en hydrogene neutre sont tres faibles, jusqu'a dix millions de fois inferieures a celles detectables par leur emission. Cette these etudie trois grandes classes de systemes en absorption. La foret lyman-alpha, constituee d'un grand nombre de raies lyman-alpha en absorption a des decalages spectraux differents, est en partie due a des halos galactiques geants, de 200 kiloparsecs de rayon (pour une constante de hubble egale a 50 kilometres par seconde et par megaparsec). La grande majorite de ces absorptions serait par ailleurs due a du gaz reparti le long des grandes structures de l'univers. Par ailleurs, une etude statistique a permis de confirmer que les systemes magnesium-deux en absorption sont effectivement dus a des halos de galaxies brillantes, de 50 a 70 kiloparsecs de rayon, comme suggere par les premieres identifications, et non a des galaxies naines groupees autour de galaxies brillantes. Enfin, un programme d'observation en cours grace au telescope spatial hubble nous permettra d'etudier les systemes lyman-alpha amortis, caracteristiques des densites de surface tres importantes. Les resultats preliminaires montrent que les parties internes des galaxies sont a l'origine de ces absorptions

We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. We analyse the spectra of 100 quasars with 3.5 < z(em) < 4.5, observed with X-shooter/Very Large Telescope in the context of the XQ-100 Legacy Survey. We detect an similar to 8 sigma excess in the CIV number density within 10 000 km s(-1) of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000 km s(-1) cutoff traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10 000 km s(-1) when weak absorbers (equivalent width < 0.2 angstrom) are also considered. We infer NV is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion, we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 per cent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by C II) along the line of sight connected to the quasar host galaxy, in contrast with what is observed in the transverse direction.

In this thesis, I present my work on the characterization of quasar outflows which I carried out using the statistics and the ionization properties of Narrow Absorption Lines (NALs). The study is based on a new sample of intermediate resolution spectra of 100 high-redshift quasars (z_em = 3.5 − 4.5), obtained with X-shooter at the European Southern Observatory Very Large Telescope, in the context of the XQ-100 Legacy Survey (Lopez et al., 2016). The combination of high signal-to-noise ratio (S/N), wide wavelength coverage and moderate spectral resolution of this survey have allowed me to look for empirical signatures to distinguish between two classes of absorbers: intrinsic (produced in gas that is physically associated with the quasar) and intervening, without taking into account any a priori definition or velocity cut-off. Previous studies have shown that NALs tend to cluster near the quasar emission redshift, at z_abs = z_em. I detect a significant excess of absorbers over what is expected from randomly distributed intervening structures. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. Most interestingly, it extends far beyond the standard 5000 km/s cut-off traditionally defined for associated absorption lines. I take advantage of the large spectral coverage of the XQ-100 spectra to study the relative numbers of NALs in different transitions, indicative of the ionization structure of the absorbers and their locations relative to the continuum source. Among the ions examined in this work, NV is the ion that best traces the effects of the quasar ionization field, offering an excellent statistical tool to identify intrinsic systems and derive the fraction of quasar driving outflows. I also test the robustness of the use of NV as additional criterium to select intrinsic NALs, performing a stack analysis of the Lya forest of the XQ-100 sample, to search for NV signal at large velocity offsets. Lastly, I compare the properties of the material along the quasar line of sight, derived from my sample, with results based on close quasar pairs investigating the transverse direction. I find a deficiency of cool gas (traced by CII) along the line of sight connected to the quasar host galaxy, in contrast with what is observed in the transverse direction in agreement with the predictions of the AGN unification models.

Modern cosmology predicts that a galaxy overdensity (e.g., protocluster) will be associated with a large intergalactic medium gas reservoir, which can be traced by Ly alpha forest absorption. We have undertaken a systematic study of the relation between Coherently Strong intergalactic Lya Absorption systems (CoSLAs), which have the highest optical depth (tau) in the tau distribution, and mass overdensities on the scales of similar to 10-20 h(-1) comoving Mpc. On such large scales, our cosmological simulations show a strong correlation between the effective optical depth (tau(eff)) of the CoSLAs and the three-dimensional mass overdensity. In spectra with moderate signal-to-noise ratio, however, the profiles of CoSLAs can be confused with individual high column density absorbers. For z > 2.6, where the corresponding Ly beta is redshifted to the optical, we have developed a selection technique to distinguish between these two alternatives. We have applied this technique to similar to 6000 sight lines provided by Sloan Digital Sky Survey III quasar survey at z = 2.6-3.3 with a continuum-to-noise ratio greater than 8, and we present a sample of five CoSLA candidates with tau(eff) on 15 h(-1) Mpc greater than 4.5x the mean optical depth. At lower redshifts of z < 2.6, where the background quasar density is higher, the overdensity can be traced by intergalactic absorption groups using multiple sight lines with small angular separations. Our overdensity searches fully use the current and next generation of Ly alpha forest surveys, which cover a survey volume of > 1 (h(-1) Gpc)(3). Systems traced by CoSLAs will yield a uniform sample of the most massive overdensities at z > 2 to provide stringent constraints to models of structure formation.

Premiere partie: evolution cosmologique des systemes civ. Etude statistique de la distribution en redshift. Donnees relatives aux raies fe ii et mg ii de systemes civ deja connus confirmant la presence de 2 phases distinctes: la premiere fortement ionisee de type "halo" et l'autre de type "disque". Pour deux cas etudies, on montre qu'une galaxie appartenant a l'amas contenant le quasar est responsable des raies d'absorptions. Deuxieme partie, travaux relatifs au milieu interstellaire. Transfert de rayonnement par les poussieres dans un milieu inhomogene

We present Hubble Space Telescope far-UV spectra of four QSOs whose sightlines pass through the halo of NGC 1097 at impact parameters of rho = 48-165 kpc. NGC 1097 is a nearby spiral galaxy that has undergone at least two minor merger events, but no apparent major mergers, and is relatively isolated with respect to other nearby bright galaxies. This makes NGC 1097 a good case study for exploring baryons in a paradigmatic bright-galaxy halo. Ly alpha absorption is detected along all sightlines and Si III lambda 1206 is found along the three sightlines with the smallest.; metal lines of C II, Si II, and Si IV are only found with certainty toward the innermost sightline. The kinematics of the absorption lines are best replicated by a model with a disk-like distribution of gas approximately planar to the observed 21 cm H I disk, which is rotating more slowly than the inner disk, and into which gas is infalling from the intergalactic medium. Some part of the absorption toward the innermost sightline may arise either from a small-scale outflow or from tidal debris associated with the minor merger that gives rise to the well known "dog-leg" stellar stream that projects from NGC 1097. When compared to other studies, NGC 1097 appears to be a "typical" absorber, although the large dispersion in absorption line column density and equivalent width in a single halo goes perhaps some way toward explaining the wide range of these values seen in higher-z studies.

L’évolution des galaxies est un sujet relativement débattu en astronomie extra-galactique, étant donné que la plupart des mécanismes responsables des propriétés observées dans les galaxies (masse, taux de formation d’étoiles, contenu en métaux, moment angulaire) sont encore peu contraints et certains ne sont probablement même pas encore observés. Ma thèse porte sur une analyse de la région entourant les galaxies, connue sous le nom de Milieu Circum Galactique (MCG). Le MCG est à l’interface entreles galaxies et le Milieu Inter Galactique (MIG) et est considéré comme le lieu de prédilection pour les échanges gazeux et énergétiques entre les galaxies et le MIG, ce qui en fait la clé pour une meilleure compréhension de l’évolution des galaxies et du destin des baryons. Je présenterai dans un premier temps l’analyse d’un échantillon de systèmes à forte absorption issuent de la spectroscopie de quasars en absorption qui tracent les régions denses en hydrogène généralement associées au MCG des galaxies.Dans un deuxième temps, je présenterai ma contribution au développement d’une mission ballon embarquant un spectrographe UV, FIREBall-2, spécialement conçu pour observer l’émission faible et diffuse du MCG des galaxies à décalage vers le rouge inférieur à 1. D’un point de vue technique, je présenterai l’étude du composant optique clé de l’instrument: le réseau. D’un point de vue modélisation, je décrirai une simulation complète des observations, qui servira à la préparation du vol prévu pour l’Automne 2017notamment en ce qui concerne la sélection des cibles, la stratégie observationelle et le traitement des données
The evolution of galaxies is a rather hot topic in extra galactic astronomy, as many of the main mechanisms underlying the observed properties of galaxies (mass, star formation rate, metal content, angular momentum) are still poorly constraints and many of them are probably undiscovered yet. My thesis focuses on an analysis of the region surrounding galaxies, known as the Circum Galactic Medium (CGM). The CGMinterfaces the galaxy with the Inter Galactic Medium (IGM) and is thought to be the most active location for gas and energy exchanges (in and out), which makes it a key ingredient towards a better understanding of galaxy evolution and the fate of all baryons. I will present in a first part, the analysis of a sample of strong absorption features based on quasar absorption spectroscopy, that probe the dense neutral hydrogen usually associated with galaxies’ CGM. In a second part, I will present my contribution to the development of a balloon-borne UV spectrograph, FIREBall-2, specifically designed to observe the faint and diffuse emissions from the CGM of galaxies at redshifts below 1. On the technical side, I will present the characterization of the key optical component ofthe instrument: the grating. On the modeling side, I will focus on an end-to-end pixel simulation of the observations to prepare for the upcoming flight, planned for Autumn 2017, in terms of target selection, observational strategy and data analysis

From the introduction: "In this Thesis work we focus on the fundamental role that the Square Kilometre Array (SKA) will play in the search for Radio Recombination Lines (RRLs) from quasars and in radio-continuum observations of large scale structures, as, e.g. galaxy clusters. Moreover, we investigate the relationship between quasars and their host galaxies through studies of the cosmic LSS".

We report the first detection of extended neutral hydrogen (H I) gas in the interstellar medium (ISM) of a massive elliptical galaxy beyond z similar to 0. The observations utilize the doubly lensed images of QSO HE 0047-1756 at z(QSO) = 1.676 as absorption-line probes of the ISM in the massive (M-star approximate to 10(11) M-circle dot) elliptical lens at z = 0.408, detecting gas at projected distances of d = 3.3 and 4.6 kpc on opposite sides of the lens. Using the Space Telescope Imaging Spectrograph, we obtain UV absorption spectra of the lensed QSO and identify a prominent flux discontinuity and associated absorption features matching the Lyman series transitions at z = 0.408 in both sightlines. The H I column density is log N(H I)= 19.6-19.7 at both locations across the lens, comparable to what is seen in 21 cm images of nearby ellipticals. The H I gas kinematics are well-matched with the kinematics of the Fe II absorption complex revealed in ground-based echelle data, displaying a large velocity shear of approximate to 360 km s(-1) across the galaxy. We estimate an ISM Fe abundance of 0.3-0.4 solar at both locations. Including likely dust depletions increases the estimated Fe abundances to solar or supersolar, similar to those of the hot ISM and stars of nearby ellipticals. Assuming 100% covering fraction of this Fe-enriched gas, we infer a total Fe mass of M-cool(Fe) similar to (5-8) x 10(4) M-circle dot in the cool ISM of the massive elliptical lens, which is no more than 5% of the total Fe mass observed in the hot ISM.

In this thesis we investigate the large-scale distribution of Ly alpha forest absorption, the effect of ionizing radiation from QSOs on their surrounding intergalactic medium and the primordial abundance of deuterium. We develop a new technique for detecting structure on Mpc scales in the Ly alpha forest. This technique does not rely on identifying individual absorption lines but is rather based on the statistics of the transmitted flux. We demonstrate that the new method is significantly more sensitive to the presence of large-scale structure in the Ly alpha forest than a two-point correlation function analysis. We apply this method to 2 A resolution spectra of ten QSOs which cover the redshift range 2.2 < z < 3.4. The QSOs form a closely spaced group on the sky and are concentrated within a 1-deg^2 field. We find evidence for large-scale structure in the distribution of Ly alpha forest absorption at the > 99 per cent confidence level. Along the line of sight we find overdense Ly alpha absorption on scales of up to 1200 km s^-1. There is also strong evidence for correlated absorption across line of sight pairs separated by < 3 h^-1 Mpc. For larger separations the cross-correlation signal becomes progressively less significant. Using the same technique and dataset we confirm the existence of the proximity effect. We derive a value for the mean intensity of the extragalactic background radiation at the Lyman limit of J = (3.6^+3.5_-1.3) x 10^-22 ergs s^-1 cm^-2 Hz^-1 sr^-1. This value assumes that QSO redshifts measured from high ionization lines differ from the true systemic redshifts by Delta v = 800 km s^-1. Allowing for known QSO variability we find evidence at a level of 2.1 sigma that the significance of the proximity effect is correlated with QSO Lyman limit luminosity. From the complete sample we find no evidence for the existence of a foreground proximity effect, implying either that J > 20 x 10^-22 ergs s^-1 cm^-2 Hz^-1 sr^-1 or that QSOs emit at least a factor of 1.4 less ionizing radiation in the plane of the sky than along the line of sight to Earth. We do, however, find one counter-example where a foreground QSO apparently depletes the absorbing gas in four surrounding lines of sight. We discuss the feasibility of pre-selecting absorption systems from low resolution data for a measurement of the primordial deuterium abundance. We present a new, low resolution spectroscopic survey of 101 high redshift QSOs aimed at identifying candidate D/H systems. We further present an echelle spectrum of a Lyman limit system at z = 2.917. We find that this system is most likely heavily contaminated and does not yield an interesting limit on D/H.

We present multisightline absorption spectroscopy of cool gas around three lensing galaxies at z = 0.4-0.7. These lenses have half-light radii r(e) = 2.6-8 kpc and stellar masses of log M-*/M-circle dot = 10.9-11.4, and therefore resemble nearby passive elliptical galaxies. The lensed QSO sightlines presented here occur at projected distances of d = 3-15 kpc (or d approximate to 1-2 r(e)) from the lensing galaxies, providing for the first time an opportunity to probe both interstellar gas at r similar to r(e) and circumgalactic gas at larger radii r >> r(e) of these distant quiescent galaxies. We observe distinct gas absorption properties among different lenses and among sightlines of individual lenses. Specifically, while the quadruple lens for HE 0435-1223 shows no absorption features to very sensitive limits along all four sightlines, strong MgII, Fe II, Mg I, and Ca II absorption transitions are detected along both sightlines near the double lens for HE 0047-1756, and in one of the two sightlines near the double lens for HE 1104-1805. The absorbers are resolved into 8-15 individual components with a line-of-sight velocity spread of Delta v approximate to 300-600 km s(-1). The large ionic column densities, log N greater than or similar to 14, observed in two components suggest that these may be Lyman limit or damped Ly a absorbers with a significant neutral hydrogen fraction. The majority of the absorbing components exhibit a uniform supersolar Fe/Mg ratio with a scatter of < 0.1 dex across the full Delta v range. Given a predominantly old stellar population in these lensing galaxies, we argue that the observed large velocity width and Fe-rich abundance pattern can be explained by SNe Ia enriched gas at radius r similar to r(e). We show that additional spatial constraints in line-of-sight velocity and relative abundance ratios afforded by a multisightline approach provide a powerful tool to resolve the origin of chemically enriched cool gas in massive haloes.

Using Hubble Space Telescope Cosmic Origins Spectrograph observations of 89 QSO sightlines through the Sloan Digital Sky Survey footprint, we study the relationships between C IV absorption systems and the properties of nearby galaxies, as well as the large-scale environment. To maintain sensitivity to very faint galaxies, we restrict our sample to 0.0015 < z < 0.015, which defines a complete galaxy survey to L (SIC) 0.01 L-* or stellar mass M-* (SIC) 10(8) M-circle dot. We report two principal findings. First, for galaxies with impact parameter rho < 1 r(vir), C IV detection strongly depends on the luminosity/stellar mass of the nearby galaxy. C IV is preferentially associated with galaxies with M-* > 10(9.5) M-circle dot; lower-mass galaxies rarely exhibit significant C IV absorption (covering fraction f(C) = 9(-6)(+12)% for 11 galaxies with M-* < 10(9.5) M-circle dot.). Second, C IV detection within the M-* > 10(9.5) M-circle dot. population depends on environment. Using a fixed-aperture environmental density metric for galaxies with rho < 160 kpc at z < 0.055, we find that 57(-13)(+12)% (8/14) of galaxies in low-density regions (regions with fewer than seven L > 0.15 L* galaxies within 1.5 Mpc) have affiliated C IV absorption; however, none (0/7) of the galaxies in denser regions show C IV. Similarly, the C IV detection rate is lower for galaxies residing in groups with dark matter halo masses of M-halo > 10(12.5) M-circle dot. In contrast to C IV, H. I is pervasive in the circumgalactic medium without regard to mass or environment. These results indicate that C IV absorbers with log N(C IV). (SIC) 13.5 cm(-2) trace the halos of M-* > 10(9.5) M-circle dot galaxies but also reflect larger-scale environmental conditions.

The work we present in this manuscript revolves around the use of quasar spectra to probe the Universe. Absorption features in the electromagnetic spectrum of bright distant quasars by ionized hydrogen give us access to the distribution of gas in the Universe. Because the light from distant quasars is redshifted as it travels through the Universe, photons emitted with an energy below the Lyα transition will be absorbed along their journey, at the point where their wavelength has been redshifted to the transition wave- length of 1216 Å. As a result, an observed spectrum and its features, referred to as Lyα Forest, depend on the density of neutral hydrogen as a function of position along the line of sight from the quasar. Similar studies can be made with photons blueward of the emission line of the triply ionized carbon. Studying the distribution of this ionized gas on cosmological scales allows us to trace the underlying matter density field while at the same time gaining insight on the thermal state of the intergalactic medium by studying the small-scale correlations of the Lyα absorption. Part I of this manuscript, Introduction to the Universe introduces all the physical and observational notions necessary for the understanding of this doctoral work. In chapter 1, we put in context the field of cosmology and its motivations as well as acquaint ourselves with the standard models that made consensus as best describing our Universe at this time. Chapter 2 presents the formalism and notions of cosmology used in the following chapters. Additional clarifications are available for the interested reader in appendix A. Chapter 3 introduces useful concepts for the use of quasars and their spectra as observables for cosmological surveys. Part II starts with chapter 4, On the effect of the ionizing background on the Lyα forest autocorrelation function. In this work, we present an analytical frame- work to understand the effects of a fluctuating intensity of the cosmic ionizing background on the correlations of the Lyα Forest transmission fraction measured in quasar spectra. In the absence of intensity fluctuations, , and in the limit of large scales at which the linear regime is applicable, the Lyα power spectrum should have the expected cold dark matter power spectrum with redshift distortions in the linear regime, with a bias factor bδ and a redshift distortion parameter β that depend on redshift but are independent of scale. We found that the intensity fluctuations introduce a scale dependence in both bδ and β, but keeping their product bδβ fixed. We also showed that these fluctuations do not bias current or future measurements of the baryon acoustic oscillation (BAO) scale from Lyα Forest. Only the amplitude of the Lyα autocorrelation is affected, the position of the BAO peak is not. Chapter 5 is titled Quasar - CIV Forest cross-correlation. In a similar fash- ion that the Lyα Forest is used to probe neutral hydrogen clouds, we use the absorp- tion features of triply ionized carbon (CIV) to (a) probe metal enriched gas at redshift 1.4 < z < 4.2, (b) trace structures at z < 2 that were not accessible with the Lyα For- est. Thanks to the data provided by the full BOSS survey, there is a sufficient increase in quasar number density, compared to previous data sets available, to offset the lower sensitivity of the CIV Forest. As a result, we have made the first detection using the con- tinuum transmission approach of a signal from the Quasar - CIV forest cross-correlation. This detection allows to measure the transmission CIV bias factor at redshift z = 2.3: (1 + βCIV )bCIV = −0.024 ± 0.003.
El treball que presentem en aquesta tesi versa sobre l’ús d’espectres de quàsars per a investigar l’Univers. Els sistemes d’absorció produïts per l’hidrogen intergalàctic en l’espectre electromagnètic de quàsars llunyans i brillants ens permeten explorar la dis- tribució de gas en l’Univers. Atès que la llum dels quàsars es decala cap al roig a mesura que viatja a través de l’Univers, els fotons emesos amb una energia superior a la de la transició Lyα són absorbits (en realitat, rebotats per àtoms d’hidrogen) al llarg del seu viatge, just al punt on la seva longitud d’ona coincideix amb la línia de ressonància Lyα a 1216 Å. El resultat és el que denominem bosc Lyα , un camp d’absorció variable al llarg de l’espectre que reflecteix la densitat d’hidrogen neutre en funció de la posició al llarg de la línia de visual del quàsar. Estudis similars poden realitzar-se a la part de l’espectre cap al blau de la línia d’emissió del carboni triplement ionitzat (CIV), en què apareix absorció per part del CIV intergalàctic. La distribució d’aquest gas ionitzat a escales cosmològiques ens permet rastrejar el camp de densitat de matèria subjacent, i al mateix temps obtenir una visió de l’estat tèrmic del medi intergalàctic mitjançant l’estudi de les correlacions a petita escala de l’absorció Lyα . La part I de la tesi, Introducció a l’Univers, ens introdueix les nocions físiques i observacionals necessàries per a la comprensió d’aquest treball doctoral. En el capítol 1, posem en context el camp de la cosmologia i les seves motivacions, i presentem el model estàndard que ha assolit un consens com la millor descripció del nostre Univers en l’actualitat. Seguidament, el capítol 2 presenta el formalisme i les nocions de cosmolo- gia emprades en els segënts capítols. A l’annex A hi ha aclariments addicionals pel lector interessat. A continuació, el capítol 3 presenta conceptes útils sobre l’ús dels espectres de quàsars per estudis cosmològics. La part II comença amb el capítol 4, titolat sobre l’efecte del fons ionitzant en la funció d’autocorrelació del bosc Lyα . Aquest treball desenvolupa un marc analític per a comprendre els efectes d’una intensitat fluctuant del fons còsmic ionitzant sobre les correlacions de l’absorció en el bosc Lyα mesurades en espectres de quàsars. En absència d’aquestes fluctuacions d’intensitat, i en el límit d’escales grans en què el règim lineal és aplicable, l’espectre de potència del bosc Lyα ha de ser proporcional a l’espectre de potència de la massa en la teoria estàndard de matèria fosca freda esperada, amb les conegudes distorsions de decalatge al vermell del règim lineal, i està totalment carac- teritzat per un factor de biaix bδ i un paràmetre de distorsió per decalatge β. Aquests dos paràmetres poden evolucionar amb el temps però són independents de l’escala. En el nostre treball trobem que les fluctuacions d’intensitat introdueixen una dependència d’escala tant en bδ como en β, però mantenint el seu producte bδβ fix. També mostrem que aquestes fluctuacions d’intensitat no esbiaixen de manera sistemàtica les mesures de l’escala d’oscilůlacions acústiques bariòniques (BAO) del bosc Lyα , la qual s’utilitza per indagar la presència d’energia fosca a l’Univers a les diverses èpoques en què podem mesurar aquesta escala. Només l’amplitud de l’autocorrelació Lyα es veu afectada. El capítol 5 es titula Creu-Correlació quàsars - bosc CIV. De forma semblant a com el bosc Lyα s’utilitza per a sondar els núvols d’hidrogen neutre, hem utilitzat les característiques d’absorció del CIV per traçar estructures en l’interval de decalatge 1.4 < z < 4.2, sondant el gas enriquit en metall i correlacionant-lo amb els quàsars. a. Gràcies a les dades del cartografiat complet de BOSS i al gran nombre de quàsars que inclou, hem pogut mesurar la creu-correlació de l’absorció de CIV amb quàsars amb precisió suficient per obtenir la primera mesura dels factors de biaix dels absorbidors de CIV. El resultat d’aquesta mesura pel factor de biaix de la fracció transmesa per CIV a un decalatge de z = 2.3 és: (1 + βCIV )bCIV = −0.024 ± 0.003, amb un error més gran per mesurar el factor de distorsió βCIV i bCIV separadament.
El trabajo que presentamos en este manuscrito gira en torno al uso de espectros de cuasar para investigar el Universo. Las características de absorción en el espectro electromagnético de los cuasares distantes brillantes por el hidrógeno ionizado nos dan acceso a la distribución de gas en el Universo. Debido a que la luz de cuásares distantes es redshifted a medida que viaja a través del Universo, los fotones emitidos con una energía por debajo de la transición Lyα serán absorbidos a lo largo de su viaje, en el punto donde su longitud de onda ha sido redshifted a la transición de longitud de onda de 1216 Å. Como resultado, un espectro observado y sus características, denominado Bosque Lyα , dependen de la densidad del hidrógeno neutro en función de la posición a lo largo de la línea de visión a partir del cuásar. Estudios similares pueden realizarse con fotones hacia el azul de la línea de emisión del carbono ionizado triple. El estudio de la distribución de este gas ionizado en las escalas cosmológicas nos permite rastrear el campo de densidad de materia subyacente, mientras que al mismo tiempo obtener una visión sobre el estado térmico del medio intergaláctico mediante el estudio de las correlaciones a pequeña escala de la absorción de Lyα . La parte I de este manuscrito, Introducción al Universo, introduce todas las no- ciones físicas y observacionales necesarias para la comprensión de este trabajo doctoral. En el capítulo 1, ponemos en contexto el campo de la cosmología y sus motivaciones, así como nos acostumbramos a los modelos estándares que hicieron del consenso como la mejor descripción de nuestro Universo en este momento. El capítulo 2 presenta el formalismo y las nociones de cosmología utilizadas en los siguientes capítulos. En el apéndice A se encuentran aclaraciones adicionales para el lector interesado. Por último, el capítulo 3 presenta conceptos útiles para el uso de cuásares y sus espectros como ob- servables para estudios cosmológicos. La parte II comienza con el capítulo 4, Sobre el efecto del fondo ionizante en la función de autocorrelación del bosque Lyα . En este trabajo se presenta un marco analítico para comprender los efectos de una intensidad fluctuante del fondo ionizante cósmico sobre las correlaciones de la fracción de transmisión de Lyα bosque medido en espectros de cuasar. En ausencia de fluctuaciones de intensidad, y en el límite de grandes escalas en las que el régimen lineal es aplicable, el espectro de potencia Lyα debería tener el espectro de potencia de materia oscura fría esperada con distorsiones de desplazamiento al rojo en el régimen lineal, con un factor de sesgo bδ y un parámetro de distorsión de desplazamiento al rojo β que dependen del desplazamiento al rojo pero son independientes de la escala. Encontramos que las fluctuaciones de intensidad introducen una dependencia de escala tanto en bδ como en β, pero manteniendo su producto bδβ fijo. También mostraron que estas fluctuaciones no sesgo actual o futuras mediciones de la oscilación acústica barión (BAO) escala de Bosque Lyα . Sólo la amplitud de la autocorrelación Lyα se ve afectada, la posición del pico BAO no lo es. El capítulo 5 se titula Cuasar - CIV bosque correlación cruzada. De man- era similar, el bosque de Lyα se utiliza para probar las nubes de hidrógeno neutras, utilizamos las características de absorción del carbono ionizado triple (CIV) para (a) sondar el gas enriquecido en metal a cambio de rojo 1.4 < z < 4.2, (b) z < 2 que no eran accesibles con el bosque Lyα . Gracias a los datos proporcionados por la encuesta completa de BOSS, existe un aumento suficiente en la densidad del número de cuásar, en comparación con los conjuntos de datos anteriores disponibles, para contrarrestar la menor sensibilidad del bosque CIV. Como resultado, hemos hecho la primera detección usando el método de transmisión continua de una señal de la correlación cruzada del bosque Cuasar-CIV. Esta detección permite medir el factor de sesgo de transmisión CIV al desplazamiento al rojo z = 2.3: (1 + βCIV )bCIV = −0.024 ± 0.003.

In this thesis we make a new measurement of the primordial deuterium abundance, and analyse five other systems selected as possible D/H candidates. We also undertake an investigation of systematic errors in a system where an existing deuterium measurement has been made. We measure the number of hydrogen components and their velocity distributions in a moderate and high redshift sample of Lyman limit systems in one Angstrom resolution spectra. We present a new measurement of the deuterium-to-hydrogen ratio, D/H, at z=3.2560 in a newly-discovered low metallicity absorption system towards the quasar PG1937-1009. We attempt to account for any systematic effects that could influence the D/H measurement. We find a 1 sigma range for D/H*1e5 of 1.6 (+0.25) (-0.30). Using high resolution spectra from the Hubble Space Telescope and the Very Large Telescope, we assess the suitability of five D/H candidate absorption systems. These systems were selected as candidates using lower resolution spectra. We measure the neutral hydrogen column density, identify metal lines and analyse the velocity structure of each system, and show them to be unsuitable for measuring D/H. We also investigate the systematic errors in the absorber at z=0.701 towards quasar PG1718-4801 that was initially thought to show a high primordial D/H value. We analyse the dependence of the putative deuterium line's parameters on wavelength calibration errors in the HST spectra and present a revised deuterium measurement. We examine the velocity widths of two samples of one Angstrom resolution quasar spectra showing Lyman limit absorption systems. The first sample is at high redshifts, taken from the Sloan quasar data release 3 catalogue. The second is at intermediate redshifts, compiled from a survey for UV quasar absorption systems taken with the Hubble Space Telescope. We use a modified version of the Voigt profile fitting program, VPFIT, to estimate the number of hydrogen velocity components and column density in the Lyman limit systems. We compare the velocity distributions of the higher and lower redshift samples. We find the distributions are consistent with other measures of the velocity spread in absorption systems, and find no compelling evidence for evolution between the redshift samples.

Absorption profiles are found in the observed spectra from quasars, and the most prominent of these are the Damped Lyman-alpha Absorbers (DLAs). They are caused by large collections of neutral hydrogen (HI) gas, which are thought to be housed in galaxies that lie along the line-of-sight to quasars. HI gas associated with DLAs contains most of the HI gas in the Universe during 2 < z < 5, and hence details about DLAs are important for understanding the history of star formation, as well as the formation and evolution of galaxies. Wyithe (2008) proposed a method of determining the characteristic mass of dark matter haloes that host DLAs. This involves generating an analytic power spectrum of the fluctuations in 21cm brightness temperature caused by the HI gas in the Universe. Calculating this analytic 21cm power spectrum requires a formalism for the HI mass weighted clustering bias of DLAs on both large and small scales. We include this DLA clustering bias by firstly generating an analytic galaxy power spectrum using the halo model of Peacock & Smith (2000), as well as including the occupation of haloes by galaxies -- using the Halo Occupation Distribution (HOD) weighting of Peacock (2003). This weighting is then adapted to account for the occupation of haloes by HI gas.
We then fit the analytic 21cm power spectrum generated using this formalism to a simulated 21cm power spectrum, with the characteristic mass of DLA host haloes being used as a fitting parameter. The DLA host halo mass is in turn dependent upon two parameters in our model: the minimum mass of haloes M_{min} included in our formalism, and the HI weighting index alpha_{HI}. The neutral hydrogen fraction is another parameter, which we can choose to be the same as that from our simulation volume. If we also choose a value for alpha_{HI} that is motivated by analysis of the dark matter and HI gas content of the haloes in the simulation, then we are able to fit the 21cm power spectrum at both large and small scales, with an M_{min} that is the same or similar to the lowest mass in the simulation's halo catalogue. This in turn gives a similar value for the DLA host halo mass that is known to be the case in the simulation. This demonstrates the viability of the Wyithe (2008) method for determining the DLA host halo mass using observations of 21cm fluctuations. However, degeneracies in the free parameters of our analytic formalism would hinder an accurate determination of the DLA host halo mass from actual future observations. This is due to the fact that the real space, spherically averaged 21cm power spectrum is used throughout this thesis. However, extending our analytic formalism to the redshift space, angular-dependent 21cm power spectrum should be capable of breaking the degeneracy between DLA host halo mass and neutral hydrogen fraction.

One of the most refined qualities of the human mind concerns with its natural attitude in questioning itself about the reason of everything it gets in touch with. This is a cascade process which inevitably ends up in wondering how the Universe originated and evolved into terrestrial life. In the course of ages the best approach to satisfy the human thirst of knowledge has proved to be the “scientific method”, based on the precious interplay between “tangible” (observations) and “intelligible” (theory). Cosmology is a discipline which aims, through this method, at shedding light on all the phases of the evolution of the Universe. Up to now the available technology has allowed to open and only partially come through the gates of the comprehension of the Universe...

2008/2009
The aim of this thesis work is to explore coherently different aspects related to the properties of the Intergalactic Medium (IGM) and to its chemical and physical evolution from high to low redshift, especially regarding metal enrichment and the impact of different feedback processes. In the last years, high resolution spectroscopic observations have shown that the neutral hydrogen (HI) in the IGM at redshift around three, traced by the Lyman-alpha forest lines in absorption, is subjected to metal pollution down to very low column density (10^13 atoms cm^-2) with a metallicity of about 10^-3 in solar units. Since metals are produced only by stars inside galaxies, the diffuse metals in the IGM retain an important trace of the star formation and of the feedback processes from the galaxies to the IGM. The purpose of the thesis is to identify the mechanisms responsible of the enrichment, propose some physically motivated theoretical models and compare the prediction of the models with the latest observational data. In particular we focussed on two different type of enrichment: galactic (energy and momentum driven) winds produced by "starburst" galaxies at redshift z=1.5-4 and AGN feedback associated to the energy released by gas accretion onto super-massive black holes. We analysed in detail the following aspects: dynamic and energetic of wind and AGN feedbacks, IGM contamination efficiency as a function of different astrophysical and cosmological parameters, temperature and chemical composition of the metal systems, nature of the ultraviolet ionizing background (UVB). In the first part of the thesis we investigated the properties of a particular class of cosmological objects, the so called Damped Lyman-alpha systems (DLAs). These are defined as quasar (QSO) absorption systems with neutral hydrogen column density N_HI > 2 x 10^20 atoms cm^-2 (Wolfe et al. 1986). DLAs are considered as an important reservoir and/or sink of gas for the galaxy formation process in the high redshift Universe and their HI content dominate the total neutral hydrogen budget over a large fraction of the cosmic history. The interplay between DLAs and galaxies is thereby fundamental and should be addressed by any galaxy formation model. Using parallel national and internationals supercomputers, we ran high-resolution and large box-size cosmological hydrodynamical simulations of a LambdaCDM model. The numerical code used is a modified version of the Tree Particle-Mesh Smoothed Particle Hydrodynamics code GADGET-2 (Springel 2005). The main modification consists in an accurate modelling of the chemical evolution which allow us to follow the metal release from Type II and Type Ia supernovae (SNII, SNIa), along with low and intermediate mass stars (LIMS) (see Tornatore et al. 2007). We explored the numerical convergence of some relevant physical quantities and we vary the parameters describing: the properties of galactic winds, the initial stellar mass function, the linear dark matter power spectrum and the metal enrichment pattern of the IGM around DLAs. We focussed on the properties of dark matter haloes that are likely to be the hosts of DLAs systems: we predict relatively low star formation rates (0.01-0.1 M_sun/year) and metallicities around 0.1 Z_sun, at least for the bulk of our haloes of masses between 10^9 and 10^10 h^-1 M_sun hosting DLAs. For more massive haloes metallicities and star formation rates depend on the specific wind model. We found that strong galactic winds with speed of about 600 km/s, in an energy-driven wind scenario, are needed in order to match the observed column density distribution function for DLAs and the evolution of the neutral hydrogen content with redshift. The momentum-driven implementation of the galactic wind model, that relates the speed and mass load in the wind to the properties of the dark matter haloes, shows a behaviour which is intermediate between the energy-driven galactic winds of small (100 km/s) and large (600 km/s) velocities. At z=3 the contribution of haloes of masses between 10^9 and 10^10 h^-1 M_sun, for DLAs below 10^20.8 atoms cm^-2, to the column density distribution function, is significant. By interpolating physical quantities along line-of-sights through massive haloes we qualitatively showed how different galactic wind models impact on the IGM around DLAs. Furthermore, we analysed statistics related to the velocity widths of SiII associated to DLAs: while the expanding shells of gaseous matter associated to the wind can account for the observed velocities, the metallicity in the wind seems to be rather clumpy and this produces an underestimation of the observed velocity widths. We outlined possible solutions to this problem. These results are published in the paper Tescari et al. (2009, MNRAS, 397, 411). In the second part of the thesis we turned our attention to the cosmic evolution of the CIV, i.e. triply ionized carbon. Most studies of the high redshift IGM have focussed on CIV absorption, because it is strong and lies redward of the Lyman-alpha forest. Moreover the absorption line is actually a doublet with rest frame wavelengths 1548.204 and 1550.781 Angstrom, so its identification in the observational spectra is easier because of the fixed ratio between the wavelengths of the two components. The cosmological mass density of CIV, Omega_CIV, observed as a function of redshift is a fundamental quantity closely related to the metal enrichment of the IGM. Its apparent lack of evolution in the redshift interval z=[1.5,5] (Songaila 2001; Pettini et al. 2003; Boksenberg et al. 2003) is puzzling since both the physical conditions of the IGM and the properties of the ionizing background are thought to evolve between these epochs. The most recent measurements of CIV absorptions in spectra of QSOs at z=6 seem to indicate a downturn in the CIV mass density at z>5 (Becker et al. 2009; Ryan-Weber et al. 2009). At z<1, recent results based on HST UV data (Cooksey et al. 2009) give Omega_CIV=(6 +- 1) x 10^-8 corresponding to a 2.8 +- 0.5 increase over the 1.5Lo scopo di questa tesi di dottorato è l'esplorazione coerente di diversi aspetti concernenti le proprietà del Mezzo Intergalattico (IGM) e la sua evoluzione chimica e fisica da alto a basso redshift, specialmente considerando l'arricchimento metallico e l'impatto di differenti processi di feedback. Negli ultimi anni, osservazioni spettroscopiche ad alta risoluzione hanno mostrato che l'idrogeno neutro (HI) nell'IGM a redshift circa tre, tracciato dalle linee di assorbimento della foresta Lyman-alpha, è soggetto ad arricchimento metallico fino a densità di colonna estremamente basse (10^13 atomi cm^-2) con metallicità attorno a 10^-3 in unità solari. Poiché i metalli sono prodotti solo dalle stelle all'interno delle galassie, i metalli diffusi nell'IGM conservano la traccia dei processi di formazione stellare e dei processi di feedback dalle galassie al mezzo intergalattico. Il fine di questa tesi è di identificare i meccanismi responsabili dell'arricchimento, proporre alcuni modelli teorici fisicamente plausibili e confrontare le predizioni dei modelli con i più aggiornati dati osservativi disponibili. In particolare ci siamo concentrati su due tipi distinti di arricchimento: feedback da venti galattici (sia a conservazione di energia che a conservazione di momento), prodotti da galassie "starburst" a redshift z=1.5-4, e feedback da AGN, associato all'energia rilasciata dall'accrescimento del gas su buchi neri supermassivi. Abbiamo analizzato in dettaglio i seguenti aspetti: dinamica ed energetica dei due precedenti tipi di feedback, efficienza di contaminazione dell'IGM in funzione di differenti parametri astrofisici e cosmologici, temperatura e composizione chimica dei sistemi metallici, natura del background ionizzante ultravioletto (UVB). Nella prima parte della tesi abbiamo investigato le proprietà di una particolare classe di oggetti cosmologici, i sistemi Damped Lyman-alpha (DLAs): definiti come sistemi di assorbimento con densità di colonna in idrogeno neutro N_HI > 2 x 10^20 atomi cm^-2 (Wolfe et al. 1986). I DLAs sono considerati come un importante bacino e/o riserva di gas per i processi di formazione delle galassie ad alto redshift e contengono la maggior parte dell'idrogeno neutro dell'Universo per una larga frazione della storia cosmica. La reciproca interazione tra galassie e DLAs è quindi di fondamentale importanza e ogni modello di formazione galattica dovrebbe essere in grado di spiegarla all'interno di un contesto fisicamente plausibile. Usando supercomputer in Italia e all'estero, abbiamo eseguito simulazioni cosmologiche idrodinamiche, ad alta risoluzione e per box di grandi dimensioni, di un modello di universo LambdaCDM. Il codice utilizzato è una versione modificata del codice TreePM-SPH GADGET-2 (Springel 2005). La modifica principale consiste in un'accurata modellizzazione dell'arricchimento chimico dovuto a supernovae di tipo Ia e di tipo II (SNIa, SNII), e a stelle di massa intermedia (LIMS) (Tornatore et al. 2007). Abbiamo analizzato la convergenza numerica di alcune quantità fisiche rilevanti e variato i parametri che descrivono: le proprietà dei venti galattici, la funzione di massa stellare iniziale (IMF), lo spettro di potenza iniziale della materia oscura e il modello di arricchimento metallico dell'IGM attorno ai DLAs. Ci siamo concentrati sulle proprietà degli aloni di materia oscura che, statisticamente, ospitano sistemi DLAs, trovando tassi di formazione stellare relativamente bassi (0.01-0.1 M_sun/anno) e metallicità attorno a 0.1 Z_sun, almeno per il grosso degli aloni con masse tra 10^9 e 10^10 h^-1 M_sun contenenti DLAs. Per aloni più massivi le metallicità e i tassi di formazione stellare dipendono dallo specifico modello di vento. Venti galattici "forti" con velocità di 600 km/s, nello scenario a conservazione di energia, riproducono la funzione di distribuzione della densità di colonna osservata per i DLAs e l'evoluzione col redshift del contenuto totale di idrogeno neutro nella box. L'implementazione dei venti galattici a conservazione del momento, che mette in stretta relazione la velocità e l'efficienza del vento con le proprietà degli aloni di materia oscura, mostra un andamento intermedio tra i venti galattici "deboli" (100 km/s) e "forti" (600 km/s) nello scenario a conservazione dell'energia. A z=3 il contributo degli aloni di massa tra 10^9 and 10^10 h^-1 M_sun alla funzione di distribuzione della densità di colonna, per DLAs con densità di colonna minori di 10^20.8 atomi cm^-2, è significativo. Interpolando quantitià fisiche di interesse lungo linee di vista attraverso gli aloni più massivi delle simulazioni abbiamo mostrato qualitativamente come i diversi modelli di vento galattico influiscono sull'IGM attorno ai DLAs. Inoltre, abbiamo analizzato statistiche relazionate alla "velocity width" del SiII associato ai DLAs: anche se le velocità delle bolle di gas espulse dai venti galattici riproducono le velocità osservate, l'arricchimento prodotto dal vento sembra essere costituito da piccoli agglomerati metallici isolati e non un arricchimento uniforme. Questo produce una sottostima delle velocity widths osservate. Possibili soluzioni a questo problema sono brevemente discusse. I risultati di questo lavoro sono stati pubblicati nell'articolo Tescari et al. (2009, MNRAS, 397, 411). Nella seconda parte della tesi ci siamo focalizzati sull'evoluzione cosmica del CIV, cioè il carbonio tre volte ionizzato. Molti studi dell'IGM ad alto redshift si basano sull'analisi delle righe di assorbimento del CIV, perché sono ben definite e marcate e si situano a lunghezza d'onda superiore rispetto alla foresta Lyman-alpha, non essendone pertanto contaminate. Inoltre, la linea di assorbimento è in realtà un doppietto con lunghezze d'onda a riposo di 1548.204 e 1550.781 Angstrom, per cui la sua identificazione nello spettro è più facile per via della distanza fissata tra le lunghezze d'onda delle due componenti. La densità di massa cosmologica in CIV, Omega_CIV, osservata in funzione del redshift è una quantità fondamentale strettamente correlata all'arricchimento chimico dell'IGM. La sua apparente mancanza di evoluzione nell'intervallo di redshift z=[1.5,5] (Songaila 2001; Pettini et al. 2003; Boksenberg et al. 2003) è interessante poiché sia le condizioni fisiche dell'IGM che le proprietà del background ionizzante ultravioletto evolvono tra queste due epoche. Le più recenti osservazioni delle righe di assorbimento del CIV in spettri di quasars (QSOs) a z=6, sembrano indicare una flessione nella densità di massa in CIV a z>5 (Becker et al. 2009; Ryan-Weber et al. 2009). A z<1, risultati recenti basati su dati HST in banda UV (Cooksey et al. 2009) danno come risultato Omega_CIV=(6 +- 1) x 10^-8 corrispondente a un incremento di 2.8 +- 0.5 rispetto ai valori a 1.5XXII Ciclo
1980

The absorption lines found in the spectra of distant quasars provide a unique method of probing the physical conditions in the universe at early epochs. This thesis describes a study of the Lyman alpha forest absorption systems seen in the spectra of high redshift QSOs. The Anglo-Australian Telescope has been used to obtain high resolution spectra of several bright QSOs. Considerable effort has gone into developing statistical techniques for profile fitting to the data to objectively and reliably extract the parameters associated with each absorbing cloud. The distribution functions for these are given and discussed. Particular attention has been paid to the clustering properties of the Lyman alpha clouds and it is found that they are weakly (but significantly) clustered on small velocity scales. Possible interpretations of this result are discussed. One especially interesting aspect of QSO absorption systems concerns the potential for measuring, or obtaining limits on, the deuterium to hydrogen abundance at high redshifts. A knowledge of this quantity is important for constraining cosmological models and can also help us to understand the chemical evolution of light elements in galaxies. A series of numerical simulations has been carried out to explore the potential for such measurements and an absorption system has been analysed to obtain an upper limit to D/H at z = 3.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.
Includes bibliographical references (p. 43-44).
We present results on the evolution of Ly[alpha] absorption at low redshift, and the first systematic search for Si II absorption systems in the low redshift IGM. Our sample consists of 832 Ly[alpha] absorbers from 328 spectra of 204 QSOs taken from the Hubble Space Telescope archive. We develop a new, reproducible method of quasar continuum fitting, designed to quickly identify absorption lines and measure the relative line strength (a proxy for equivalent width). Our method, which fails to identify the weakest lines, does manage to detect the strong features in a given spectrum and provides enough information to identify metal absorption line systems. We confirm the results of previous studies of Ly[alpha] evolution at low redshift and find the number density of absorbers can be described by a power law in (l+z) that is much flatter than that found for Lya evolution at high redshift. Specifically, we measure a power law index of [gamma] = 0.57 ± 0.16 for lines with a rest relative line strength greater than 0.10 [Angstroms]. We also identify the presence of 14 Si II systems at z [approx] 1. The number of Si ii 1193 and 1260 [Angstroms] systems per unit redshift path length at a mean redshift of z = 0.9 is < N(z) >= 1.6 ± 0.6. This density is similar to that found for C Ii, Mg ii, and O vi absorbers.
by Adam A. Miller.
S.B.

In this thesis, we examine the relationship between the metal-enriched intergalactic medium (IGM) and galaxies at z < 1. In particular, we investigate the nature and consequence of feedback from active galactic nuclei (AGN) and supernovae, which shape the evolution of galaxies and are responsible for enriching the IGM with metals. The IGM is surveyed in ultraviolet (UV) absorption lines against background quasars (QSOs), whilst galaxies are surveyed in emission by means of optical photometry and spectroscopy. Simulated samples of IGM absorption systems and galaxies are also extracted from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological hydrodynamical simulation for critical comparison with the data. We present the results of two primary studies that are designed to address key questions on the nature and consequence of feedback: 1. We examine complex absorption profiles in the spectrum of a QSO at z ~ 1, that trace a metal-rich outflow originating from the host galaxy. We show that these absorption profiles originate from dense, sub-pc scale gas clumps at distances of a few kpc from the central AGN. The gas is likely to be dynamically unstable, and is potentially far from ionization equilibrium. We favour a scenario in which the clumps are formed in-situ, and are entrained in a hot (T > 10^6 K) outflowing wind that may trace the majority of the mass, but is undetected in the UV. These observations provide a detailed set of constraints on the nature of feedback in QSO host galaxies. 2. We investigate the distribution and dynamics of metal-enriched gas around galaxies at z < 1 through the two-point cross- and auto-correlation functions of OVI absorbers and galaxies.

I investigate the chemical evolution of the Universe in a series of cosmological hydrodynamic simulations with the purpose of finding a self-consistent evolutionary scenario of galaxy formation able to reproduce key observables focusing on the enrichment of the intergalactic medium (IGM). The most successful models I run and analyze use the scalings of momentum-driven feedback whereby UV photons generated during the Main Sequence stage accelerate dust-driven winds while providing a significantly larger energy budget than from supernovae alone. The success of this outflow model relies on its ability to drive highly mass-loaded winds from small galactic haloes. These feedback relations, supported by observations of local starburst, are inserted into simulations at all epochs, reproducing observables including the C IV column density and linewidth distributions at z=6->1.5 and the O VI forest at z=0-0.5. Outflows at z>=5 propagate early nucleosynthetic products traced by C IV and lower ionization species into an otherwise metal-free IGM. Continual outflows at the peak ages of star formation (z=5->1.5) produce a non-evolving cosmic mass density of C IV despite continual enrichment increasing IGM metallicity by a factor of ten. The z=0-0.5 O VI forest is composed of weaker absorbers tracing photo-ionized diffuse IGM metals, sometimes injected by primordial galaxies, and stronger absorbers tracing recently injected metals, often unable to escape their parent haloes and sometimes collisionally ionized. Tracking the individual histories of metals in outflows shows the average outflow travels ~100 physical kpc and returns to galaxies on an average timescale of 1-2 Gyr; this result implies metals in superwinds do not remain in the IGM for a Hubble time and are more likely to rejoin galaxies. Metal absorbers aligned with Lyman-alpha are examined in detail, finding that the two often trace different phases of gas with the former tracing an inhomogeneous distribution of metals exhibiting turbulence imparted during the outflow phase dissipating on a Hubble timescale. I find this is the first model to self-consistently reproduce the wide range of IGM observables spanning the history of heavy metal production while being consistent with key galaxy observables. The link between star formation and galactic superwinds requires that a successful model of galaxy formation reproduces both the evolution of galaxies and the IGM.

My dissertation focuses on a relatively new field of study: the region immediately around galaxies known as the circumgalactic medium (CGM). The CGM holds vast quantities of mass and metals, yet its connection to galaxies is not well understood. My work uses cosmological hydrodynamic simulations and comparisons to data from Hubble's Cosmic Origins Spectrograph (COS) to understand the CGM's connection to galaxy evolution, gas accretion, outflows, star formation, and baryon cycling. This includes studies of the CGM's extent and physical conditions; the cause and nature of outflows; gas dynamics, including the first comprehensive study of tracers of inflowing and outflowing gas at low redshift (z=0.25); and direct comparison of theoretical results to observational data. Chapter 1 introduces my research and show its connection to galaxy evolution. Chapter 2 investigates hydrogen and metal line absorption around low-redshift galaxies in cosmological hydrodynamic simulations. This chapter studies different models for stellar outflows, physical conditions, and dependencies on halo mass. Chapter 3 examines the flow of gas into, out of, and around galaxies using a novel particle tracking technique. This chapter examines the baryon cycle in detail for our preferred model of stellar outflows. Chapter 4 compares our model results, including two separate prescriptions for outflows, with data from COS. We contrast these wind models, showing how they cycle baryons differently, and show degeneracies in observational diagnostics. In Chapter 5, I summarize and discuss plans for future research in this field, and how it can be more fully leveraged to understand galaxy evolution.