A very faint spectroscopic quasar survey was undertaken in order to define the statistical behavior of the low luminosity portion of the quasar population at high redshift and to search for evidence of a decline in space density. Both slitless and multi-aperture spectroscopic observations were obtained for approximately 750 objects with B magnitudes in the range 20 < B < 24. The total number of emission line candidates found was ~ 50 and there are 5 excellent quasar candidates, 3 very probably at high redshift. In addition to the quasar candidates a number of emission line galaxies have been identified. / Graduate

Luminous quasars at z > 5.6 can be studied in detail with the current generation of telescopes and provide us with unique information on the first gigayear of the universe. Thus far, these studies have been statistically limited by the number of quasars known at these redshifts. Such quasars are rare, and therefore, wide-field surveys are required to identify them, and multiwavelength data are required to separate them efficiently from their main contaminants, the far more numerous cool dwarfs. In this paper, we update and extend the selection for the z similar to 6 quasars presented in Banados et al. (2014) using the Pan- STARRS1 (PS1) survey. We present the PS1 distant quasar sample, which currently consists of 124 quasars in the redshift range 5.6 less than or similar to z less than or similar to 6.7 that satisfy our selection criteria. Of these quasars, 77 have been discovered with PS1, and 63 of them are newly identified in this paper. We present the composite spectra of the PS1 distant quasar sample. This sample spans a factor of similar to 20 in luminosity and shows a variety of emission line properties. The number of quasars at z > 5.6 presented in this work almost doubles the previously known quasars at these redshifts, marking a transition phase from studies of individual sources to statistical studies of the high-redshift quasar population, which was impossible with earlier, smaller samples.

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.

The evolution of radio loud quasars is found to be strongly dependent upon their galaxy cluster environment. Previous studies (Yee and Green 1987) have shown that bright quasars at z ∼ 0.6 are found in clusters as rich as Abell richness class 1, while high luminosity quasars at lower redshifts are found only in poorer environments. An observational study of the environments of 66 low luminosity quasars with 0.3 < z < 0.6 yields several objects in rich clusters of galaxies. This result implies that radio loud quasars in these environments have faded approximately 3 magnitudes in the interval between redshifts 0.6 and 0.4, corresponding to a luminosity e-folding fading time of 900 million years, similar to the dynamical timescale of these environments. The analysis of low luminosity radio quiet quasars indicate that they are never found in rich environments, suggesting that they are a physically different class of objects. Properties of the quasar environment are investigated to determine constraints on the physical mechanisms of quasar formation and evolution. The optical cluster morphology indicates that the cluster cores have smaller radii and higher galaxy densities than are typical for low redshift clusters of similar richness. Radio morphologies may indicate that the formation of a dense intra-cluster medium is associated with the quasars' fading at these epochs. Galaxy colors appear to be normal, but there may be a tendency for clusters associated with high luminosity quasars to contain a higher fraction of gas-rich galaxies than those associated with low luminosity quasars, a result consistent with the formation of an ICM. Multislit spectroscopic observations of galaxies associated with high luminosity quasars indicate that quasars are preferentially located in regions of low relative velocity dispersion, either in rich clusters of abnormally low velocity dispersion, or in poor groups which are dynamically normal. This suggests that galaxy-galaxy interactions may play a role in quasar formation and sustenance. Virialization of rich clusters and the subsequent increase in galaxy velocities may therefore be responsible for the fading of quasars in rich environments.

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No description available.

We present the Swift optical to X-ray spectral energy distributions (SEDs) of 44 quasars at redshifts z approximate to 2 observed by Swift, part of a larger program to establish and characterize the optical through X-ray SEDs of moderate-redshift quasars. Here, we outline our analysis approach and present preliminary analysis and results for the first third of the full quasar sample. Not all quasars in the sample are detected in X-rays; all of the X-ray-detected objects so far are radio loud. As expected for radio-loud objects, they are X-ray bright relative to radioquiet quasars of comparable optical luminosities, with an average alpha(ox) = 1.39 +/- 0.03 (where alpha(ox) is the power-law slope connecting the monochromatic flux at 2500 angstrom and at 2 keV), and display hard X-ray spectra. We find integrated 3000 angstrom-25 keV accretion luminosities of between 0.7 x 10(46) erg s (1) and 5.2 x 10(47) erg s (1). Based on single-epoch spectroscopic virial black hole mass estimates, we find that these quasars are accreting at substantial Eddington fractions, 0.1 less than or similar to L/L-Edd less than or similar to 1.

No description available.

No description available.

We present the Data Release 12 Quasar catalog (DR12Q) from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. This catalog includes all SDSS-III /BOSS objects that were spectroscopically targeted as quasar candidates during the full survey and that are confirmed as quasars via visual inspection of the spectra, have luminosities Mi[z = 2] < -20.5 (in a Lambda CDM cosmology with H-0 = 70 km s (1) Mpc (1), Omega(M) = 0 : 3, and Omega(A) = 0.7), and either display at least one emission line with a full width at half maximum (FWHM) larger than 500 km s (1) or, if not, have interesting /complex absorption features. The catalog also includes previously known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. The catalog contains 297 301 quasars (272 026 are new discoveries since the beginning of SDSSIII) detected over 9376 deg(2) with robust identification and redshift measured by a combination of principal component eigenspectra. The number of quasars with z > 2.15 (184 101, of which 167 742 are new discoveries) is about an order of magnitude greater than the number of z > 2 : 15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C III], Mg II). The catalog identifies 29 580 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag together with some information on the optical morphology and the selection criteria. When available, the catalog also provides information on the optical variability of quasars using SDSS and Palomar Transient Factory multi-epoch photometry. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3600-10 500 a at a spectral resolution in the range 1300 < R < 2500, can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 4841 quasars that have been identified serendipitously outside of the superset defined to derive the main quasar catalog.