THE X-RAY EVOLUTION OF INFLOWS AND OUTFLOWS IN ACTIVE GALACTIC NUCLEI

Open Access
Author:
Saez, Cristian
Graduate Program:
Astronomy and Astrophysics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 29, 2010
Committee Members:
  • Michael Eracleous/George Chartas, Dissertation Advisor
  • George Chartas, Committee Chair
  • Michael Eracleous, Committee Chair
  • Stephane Coutu, Committee Member
  • Steinn Sigurdsson, Committee Member
  • Derek Brindley Fox, Committee Member
Keywords:
  • active galactic nuclei
  • X-ray astronomy
  • AGN
  • astronomy
  • extragalactic astronomy
Abstract:
The evolution of the space density of AGNs might have spectral counterparts, which could be observable in X-rays. The main objective of this thesis is to study the spectral properties of AGNs in X-rays in order to increase our current knowledge of AGN evolution. We are especially interested in high redshift AGNs with z >1.0, because the analysis of their spectra may indicate what parameters show evolutionary trends and provide insight as to which physical processes are markers of AGN evolution. The thesis begins with an introduction and review of the scientific topics that are pursued in this study. The core of my research is presented in chapters 2, 3 and 4 of the thesis. In chapter 2, we present results from a statistical analysis of 173 bright radio-quiet AGNs selected from the Chandra Deep Field-North and Chandra Deep Field-South surveys (hereafter, CDFs) in the redshift range of 0.1 < z < 4. We find that the X-ray power-law photon index (Gamma) of radio-quiet AGNs is correlated with their 2-10 keV rest-frame X-ray luminosity (LX) at the >99.5% confidence level in two redshift bins, 0.3 < z < 0.96, and 1.5 < z < 3.3 and is slightly less significant in the redshift bin 0.96 < z < 1.5. The X-ray spectral slope steepens as the X-ray luminosity increases for AGNs in the luminosity range 10^{42} to 10^{45} erg/s. Combining our results from the CDFs with those from previous studies in the redshift range 1.5 < z < 3.3, we find that the Gamma-L_X correlation has a null-hypothesis probability of 1.6x10^{-9}. We investigate the redshift evolution of the correlation between the power-law photon index and the hard X-ray luminosity and find that the slope and offset of a linear fit to the correlation change significantly (at the > 99.9% confidence level) between redshift bins of 0.3 < z < 0.96 and 1.5 < z < 3.3. We explore physical scenarios explaining the origin of this correlation and its possible evolution with redshift in the context of steady corona models focusing on its dependency on variations of the properties of the hot corona with redshift. In chapter 3, we present results from three Suzaku observations of the z = 3.91 gravitationally lensed broad absorption line quasar APM 08279+5255. We detect strong and broad absorption at rest-frame energies of < 2 keV (low-energy) and 7-12 keV (high-energy). The detection of these features confirms the results of previous long-exposure (80-90 ks) Chandra and XMM-Newton observations. The low and high-energy absorption is detected in both the back-illuminated (BI) and front illuminated (FI) Suzaku XIS spectra (with an F-test significance of >99%). We interpret the low-energy absorption as arising from a low-ionization absorber with log (NH/cm^{-2}) ~ 23 and the high-energy absorption as due to lines arising from highly ionized (2.75 < log xi < 4.0; where xi is the ionization parameter) iron in a near-relativistic outflowing wind. Assuming this interpretation we find that the velocities in the outflow range between 0.1c and 0.6c. We constrain the angle between the outflow direction of the X-ray absorber and our line of sight to be < 36 deg. We also detect likely variability of the absorption lines (at the > 99.9% and > 98% significance levels in the FI and BI spectra, respectively) with a rest-frame time scale of ~1 month. Assuming that the detected high-energy absorption features arise from FeXXV, we estimate that the fraction of the total bolometric energy injected over the quasar's lifetime into the intergalactic medium in the form of kinetic energy to be >10%. In chapter 4, we present an expansion of our previous work on the study of X-ray outflows on APM 08279+5255. The main conclusions from our multi-epoch spectral analysis of Chandra, XMM-Newton and Suzaku observations of the z = 3.91 gravitationally lensed broad absorption line (BAL) quasar APM 08279+5255 are: 1) In every observation we confirm the presence of two strong features, one at rest-frame energies between 1-4 keV, and the other between 7-18 keV. 2) The low-energy absorption is interpreted as arising (1-4 keV rest-frame) from a low-ionization absorber with log (NH/cm^{-2}) ~ 23 and the high-energy absorption (7-18 keV rest-frame) as due to lines arising from highly ionized (3 < log xi < 4; where xi is the ionization parameter) iron in a near-relativistic outflowing wind. Assuming this interpretation, we find that the velocities on the outflow could get up to ~ 0.7c. We also present results obtained from fits to all the long exposure observations of APM 08279+5255 with a new outflow model. This model is based on CLOUDY simulations of a near relativistic quasar outflow. From the analysis of this new model we conclude that the wind is likely to get more powerful as the spectra get softer. Our results also suggest that changes in the X-ray and UV portions of the spectral energy distribution (hereafter SED) of the central source could be related to changes in the terminal velocities of the outflows. If this result is confirmed it will imply that radiation pressure is an important mechanism in producing quasar outflows. In the final chapter of the thesis, we present the conclusions and future work.