A study of UV, optical and X-ray properties of quasars

Open Access
Wu, Jian
Graduate Program:
Astronomy and Astrophysics
Doctor of Philosophy
Document Type:
Date of Defense:
May 12, 2011
Committee Members:
  • Donald P Schneider, Dissertation Advisor
  • Donald P Schneider, Committee Chair
  • Jane Camilla Charlton, Committee Chair
  • William N Brandt, Committee Member
  • Daniel E Vanden Berk, Committee Member
  • Yuexing Cindy Li, Committee Member
  • Paul Sommers, Committee Member
  • quasar
  • ultraviolet UV
  • X-ray
  • AGN
  • catalog
The rest-frame UV, optical, and X-ray are important wavebands to study quasar activities because they trace ionization phases and dynamical properties of the physical structures surrounding the central engine, including the accretion disk, the broad line region, and the outflow. This thesis investigates the correlations of spectral components (continua, emission lines and absorption lines) and the physical conditions implied by these components using well-defined samples of spectra from the archives of the Sloan Digital Sky Survey (SDSS), the Hubble Space Telescope (HST), the International Ultraviolet Explorer (IUE), the Swift Space Telescope, and the Keck Telescope. The scientific goal of these studies is to produce a set of well-documented properties of quasar UV, optical, and X-ray spectra that will provide important constraints on models of the quasar phenomenon. The UV and optical continuum properties are studied using a set of composite quasar spectra created from the SDSS quasar catalog. We discovered a dependency of the continuum shape on both quasar luminosity and redshift, and found that the Baldwin Effect, in which the equivalent width of an emission line is anti-correlated with the continuum, applies for most of the broad emission lines. Focusing on the CIV emission line, we construct a sample which consists of 272 Type 1 AGNs. An analysis of this sample indicates that the changes of the EWs are controlled by both UV and soft X-ray emissions, suggesting that the UV and X-ray emissions are closely related. We show that variability is an important contributor to the scatter of many important correlations, such as the Baldwin Effect, as well as the quasar spectral energy distribution (SED) between optical and X-ray. In order to eliminate the influence of variability, we compiled a catalog of quasars with simultaneous UV, optical and X-ray observations from the Swift gamma-ray-burst explorer. Using the Swift data, plus the photometric data from SDSS, we constructed a set of composite quasar SEDs for most of the objects in our catalog. We use this set of SEDs to constrain the amplitude of the big blue bump. We also re-visit the l_uv-alpha_ox relation and demonstrate that the dispersion of this correlation can be reduced by ~20% using this simultaneously observed sample. Quasar intrinsic absorption lines are important diagnoses of the quasar outflow. Models of intrinsic narrow absorption line systems towards three high redshift quasars from Keck/HIRES, reveals high ionization levels and super-solar metallicities of these absorbers, indicating vigorous star formation occurred before the quasars become visible.