Luminous high-redshift quasars can be used to probe of the intergalactic medium in the early universe because their UV light is absorbed by the neutral hydrogen along the line of sight. They help us to measure the neutral hydrogen fraction of the high-z universe, shedding light on the end of reionization epoch. In this paper, we present a discovery of a new quasar (PSO J006.1240+39.2219) at redshift z = 6.61 +/- 0.02 from Panoramic Survey Telescope & Rapid Response System 1.Including this quasar, there are nine quasars above z > 6.5 up to date. The estimated continuum brightness is M-1450 = -25.96 +/- 0.08. PSO J006.1240+39.2219 has a strong Ly alpha emission compared with typical low-redshift quasars, but the measured near-zone region size is R-NZ = 3.2 +/- 1.1 proper megaparsecs, which is consistent with other quasars at z similar to 6.

We report the results of a faint quasar survey in a one-square-degree field. The aim is to test the Y - K/g - z and J - K/i - Y color selection criteria for quasars at faint magnitudes to obtain a complete sample of quasars based on deep optical and near-infrared color-color selection and to measure the faint end of the quasar luminosity function (QLF) over a wide redshift range. We carried out a quasar survey based on the Y - K/g - z and J - K/i - Y quasar selection criteria, using the deep Y-band data obtained from our CFHT/WIRCam Y-band images in a two-degree field within the F22 field of the VIMOS VLT deep survey, optical co-added data from Sloan Digital Sky Survey Stripe 82 and deep near-infrared data from the UKIDSS Deep Extragalactic Survey in the same field. We discovered 25 new quasars at 0.5 < z < 4.5 and i < 22.5 mag within one-square-degree field. The survey significantly increases the number of faint quasars in this field, especially at z similar to 2-3. It confirms that our color selections are highly complete in a wide redshift range (z < 4.5), especially over the quasar number density peak at z similar to 2-3, even for faint quasars. Combining all previous known quasars and new discoveries, we construct a sample with 109 quasars and measure the binned QLF and parametric QLF. Although the sample is small, our results agree with a pure luminosity evolution at lower redshift and luminosity evolution and density evolution model at redshift z > 2.5.

We present a survey of the [C II] 158 mu m line and underlying far-infrared (FIR) dust continuum emission in a sample of 27 greater than or similar to 6 quasars using the Atacama Large Millimeter Array (ALMA) at similar to 1 '' resolution. The [C II] line was significantly detected (at > 5-sigma) in 23 sources (85%). We find typical line luminosities of L-[C (II]) = 10(9-10) L-circle dot, and an average line width of similar to 385 km s(-1). The [C II]-to-far-infrared luminosity ratios ([C II]/FIR) in our sources span one order of magnitude, highlighting a variety of conditions in the star-forming medium. Four quasar host galaxies are clearly resolved in their [C II] emission on a few kpc scales. Basic estimates of the dynamical masses of the host galaxies give masses between 2 x 10(10) and 2 x 10(11) M-circle dot, i.e., more than an order of magnitude below what is expected from local scaling relations, given the available limits on the masses of the central black holes (> 3 x 10(8) M-circle dot, assuming Eddington-limited accretion). In stacked ALMA [C II] spectra of individual sources in our sample, we find no evidence of a deviation from a single Gaussian profile. The quasar luminosity does not strongly correlate with either the [C II] luminosity or equivalent width. This survey (with typical on-source integration times of 8 minutes) showcases the unparalleled sensitivity of ALMA at millimeter wavelengths, and offers a unique reference sample for the study of the first massive galaxies in the universe.

We present reverberation mapping results from the first year of combined spectroscopic and photometric observations of the Sloan Digital Sky Survey Reverberation Mapping Project. We successfully recover reverberation time delays between the g+i band emission and the broad H beta emission line for a total of 44 quasars, and for the broad Ha emission line in 18 quasars. Time delays are computed using the JAVELIN and CREAM software and the traditional interpolated cross-correlation function (ICCF): using well-defined criteria, we report measurements of 32 H beta and 13 Ha lags with JAVELIN, 42 H beta and 17 Ha lags with CREAM, and 16 H beta and eight Ha lags with the ICCF. Lag values are generally consistent among the three methods, though we typically measure smaller uncertainties with JAVELIN and CREAM than with the ICCF, given the more physically motivated light curve interpolation and more robust statistical modeling of the former two methods. The median redshift of our H beta-detected sample of quasars is 0.53, significantly higher than that of the previous reverberation mapping sample. We find that in most objects, the time delay of the Ha emission is consistent with or slightly longer than that of H beta. We measure black hole masses using our measured time delays and line widths for these quasars. These black hole mass measurements are mostly consistent with expectations based on the local M-BH-sigma* relationship, and are also consistent with single-epoch black hole mass measurements. This work increases the current sample size of reverberation-mapped active galaxies by about two-thirds and represents the first large sample of reverberation mapping observations beyond the local universe (z < 0.3).

We present the first discoveries from a survey of z greater than or similar to 6 quasars using imaging data from the DECam Legacy Survey (DECaLS) in the optical, the UKIRT Deep Infrared Sky Survey (UKIDSS) and a preliminary version of the UKIRT Hemisphere Survey (UHS) in the near-IR, and ALLWISE in the mid-IR. DECaLS will image 9000 deg(2) of sky down to z(AB) similar to 23.0, and UKIDSS and UHS will map the northern sky at 0 < decl. < + 60 degrees, reaching J(VEGA) similar to 19.6 (5-sigma). The combination of these data sets allows us to discover quasars at redshift z greater than or similar to 7 and to conduct a complete census of the faint quasar population at z greater than or similar to 6. In this paper, we report on the selection method of our search, and on the initial discoveries of two new, faint z greater than or similar to 6 quasars and one new z = 6.63 quasar in our pilot spectroscopic observations. The two new z similar to 6 quasars are at z = 6.07 and z = 6.17 with absolute magnitudes at rest-frame wavelength 1450 angstrom being M-1450 = -25.83 and M-1450 = -25.76, respectively. These discoveries suggest that we can find quasars close to or fainter than the break magnitude of the Quasar Luminosity Function (QLF) at z greater than or similar to 6. The new z = 6.63 quasar has an absolute magnitude of M-1450 = -25.95. This demonstrates the potential of using the combined DECaLS and UKIDSS/UHS data sets to find z greater than or similar to 7 quasars. Extrapolating from previous QLF measurements, we predict that these combined data sets will yield similar to 200 z similar to 6 quasars to z(AB) < 21.5, similar to 1000 z similar to 6 quasars to z(AB) < 23, and similar to 30 quasars at z > 6.5 to J(VEGA) < 19.5.

Cette thèse s'inscrit dans le domaine d'étude de l'Univers lointain, en particulier sur l'étude d'une période méconnue de notre Univers à savoir « la ré-ionisation ». Le choix de la sonde utilisée pour l'étude d'un Univers aussi lointain est quelque peu restreint. En effet il faut que la sonde soit visible à cette grande distance et donc que ce soit un objet extrêmement lumineux. Ainsi on se sert de galaxies très énergétiques avec un noyau galactique actif (appelées quasars) en tant que sonde. En étudiant le rayonnement de ces quasars on pourra alors caractériser l'environnement qui les entoure. Ces quasars étant des objets rares, il nous faut rechercher sur une grande surface du ciel pour espérer en obtenir quelques uns. Il existe beaucoup de projets d'observation dédiés à la cosmologie, un des futurs projets majeurs nommé Euclid sera un grand pas pour l'étude de la ré-ionisation. Ce futur satellite de l'ESA (lancement prévu en 2020) sera particulièrement performant dans l'infrarouge, permettant ainsi de détecter des quasars à des distances actuellement insondées. Afin de pouvoir bien préparer cette mission il nous faut établir et anticiper les performances attendues d'Euclid. Pour ce faire, il faut mener une étude similaire sur des données existantes puis extrapoler la performance d'Euclid. Pour ce faire, durant ma thèse, j'ai utilisé des données issues du télescope terrestre du CFHT (Canada France Hawaii Telescope) situé à hawaii au mont Mauna Kea. / The main topic of this thesis is the study of the distant Universe, particularly the study of a quite unknown period of our Universe namely "reionization." The probe's choice used in the study of a universe so far is somewhat restricted. Indeed it is necessary that the probe be visible at this distance and therefore the probe must be a very bright objet. Thus we used high-energy galaxies with an active galactic nuclei (called quasars) as a probe. By studying the emission of these quasars we can then characterize the environment around them. Because of the huge distance between us and the quasar and due to the expansion of the universe they have their light emissions shifted towards longer wavelengths. Thus, to study the young age of our universe, we need to observe objects in the infrared. These quasars are rare objects, we need to search over a large area of the sky to hope to get a few. There are many projects focused on observational cosmology, a future major project named Euclid will be a big step for the study of reionization. This future ESA satellite (launch planned in 2020) will be particularly effective in the infrared, thus allowing to detect quasars at distances currently unfathomed. In order to prepare this mission we must establish and predict the expected performance of Euclid. To do this, we must conduct a similar study on existing data and extrapolate the performance of Euclid. To do this, in my thesis, I used datas from the terrestrial telescope CFHT (Canada France Hawaii Telescope) located in hawaii at Mauna Kea.

We present near-infrared images of nearly 100 host galaxies of Active Galactic Nuclei (AGN). Our quasar sample is comprised of the 50 quasars from the Palomar Green Bright Quasar Survey with redshifts z ≤ 0.3. We have restricted the redshift range to ensure adequate spatial resolution, galaxy detectability, and minimal distance-dependent effects, while still giving a large sample of objects. For lower-luminosity AGN we have chosen to image the CfA Seyfert sample. This sample is composed of 48 Seyferts, roughly equally divided among types 1, 1.5-1.9, and 2. This sample was spectroscopically selected, and, therefore, is not biased towards Seyferts with significant star formation. Taken together, these samples allow a statistical look at the continuity of host galaxy properties over a factor of 10,000 in nuclear luminosity. We find the near-infrared light to be a good tracer of luminous mass in these galaxies. The Seyferts are found in galaxies of type S0 to Sc. The radio quiet quasars live in similar kinds of galaxies spanning the same range of mass centered around L*. However, for the most luminous quasars, there is a correlation between the minimum host galaxy mass and the luminosity of the active nucleus. Radio-loud quasars are generally found in hosts more massive than an L* galaxy. We also detect a population of low mass host galaxies with very low luminosity Seyfert nuclei. The low luminosity quasars and the Seyferts both tend to lie in host galaxies seen preferentially face-on, which suggests there is a substantial amount of obscuration coplanar with the galaxian disk. The obscuration must be geometrically thick (thickness-to-radius ∼ 1) and must cover a significant fraction of the narrow line region (r >100 pc). We have examined our images for signs of perturbations that could drive fuel toward the galaxy nucleus, but there are none we can identify at a significant level. The critical element for fueling is evidently not reflected clearly in the large scale distribution of luminous mass in the galaxy. We also present an infrared image of the jet of 3C 273 and compare it to optical and radio images from the literature.

No description available.

The sub-population of quasars reddened by intrinsic or intervening clouds of dust are known to be underrepresented in optical quasar surveys. By defining a complete parent sample of the brightest and spatially unresolved quasars in the COSMOS field, we quantify to which extent this sub-population is fundamental to our understanding of the true population of quasars. By using the available multiwavelength data of various surveys in the COSMOS field, we built a parent sample of 33 quasars brighter than J = 20 mag, identified by reliable X-ray to radio wavelength selection techniques. Spectroscopic follow-up with the NOT/ALFOSC was carried out for four candidate quasars that had not been targeted previously to obtain a 100% redshift completeness of the sample. The population of high AV quasars (HAQs), a specific sub-population of quasars selected from optical/near-infrared photometry, some of which were shown to be missed in large optical surveys such as SDSS, is found to contribute 21%(+9)(-5) of the parent sample. The full population of bright spatially unresolved quasars represented by our parent sample consists of 39%(+9)(-8) reddened quasars defined by having A(V) > 0.1, and 21%(+9)(-5) of the sample having E(B-V) > 0.1 assuming the extinction curve of the Small Magellanic Cloud. We show that the HAQ selection works well for selecting reddened quasars, but some are missed because their optical spectra are too blue to pass the g - r color cut in the HAQ selection. This is either due to a low degree of dust reddening or anomalous spectra. We find that the fraction of quasars with contributing light from the host galaxy, causing observed extended spatial morphology, is most dominant at z less than or similar to 1. At higher redshifts the population of spatially unresolved quasars selected by our parent sample is found to be representative of the full population of bright active galactic nuclei at J < 20 mag. This work quantifies the bias against reddened quasars in studies that are based solely on optical surveys.

No description available.