Probing Quasar Winds Using Intrinsic Narrow Absorption Lines

Open Access
Author:
Culliton, Christopher
Graduate Program:
Astronomy and Astrophysics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
November 16, 2018
Committee Members:
  • Michael Eracleous, Dissertation Advisor
  • Jane Camilla Charlton, Committee Chair
  • Jason Thomas Wright, Committee Member
  • Derek Brindley Fox, Committee Member
  • Sarah Elizabeth Shandera, Outside Member
Keywords:
  • Quasars
  • Absorption lines
  • Active Galactic Nuclei
  • Accretion Disks
Abstract:
Quasars and other active galactic nuclei (AGN) are now commonly believed to be powered through accretion of material from an accretion disk onto a supermassive black hole (SMBH), which can have an impact on the evolution of the quasar's host galaxy through feedback processes such as outflows in the form of accretion disk winds. The ultimate goal of this work is to better understand the characteristics of these outflowing winds and their relations to the host quasar. We do this using quasar spectra at both high redshift and low redshift using a combination of archival data and our own observations. First, we use the spectra of 73 quasars (1.5<z<5) from the VLT UVES archive to catalog and study narrow absorption lines (NALs, Delta v<500 km/s}) that are physically associated with (intrinsic to) the quasars. We identify 410 NAL systems containing C IV, N V, and/or Si IV doublets. Based on the assumption that only systems intrinsic to the quasar can exhibit partial coverage of the background source(s), we identify 34 reliably intrinsic NAL systems and 11 systems that are potentially intrinsic, as well as 1 broad absorption line (BAL, Delta v>2000 km/s) and 4 mini-BALs (500 km/s<Delta v<2000 km/s). The minimum fraction of quasars with at least one intrinsic system is shown to be 38%. We identify intrinsic NALs with a wide range of properties, including apparent ejection velocity, coverage fraction, and ionization level. There is a continuous distribution of properties, rather than discrete families, ranging from partially covered C IV systems with black Lya and with a separate low-ionization gas phase to partially covered N V systems with partially covered Lya and without detected low-ionization gas. Even more highly ionized associated and intrinsic absorption systems (O VI, Ne VIII, and Mg X doublets) have been presented in separate studies; these may represent an extension of the above sequence. We also use the properties of the NALs in conjunction with models of accretion disk winds (Murray et al. 1995; Proga et al. 2000; Proga & Kallman 2004; Kurosawa & Proga 2009) that predict the origins of the absorbing gas in order to determine the model that best characterizes our sample. Additionally, we construct a model describing the spatial distributions, geometries, and varied ionization structures of intrinsic NALs. Next, we searched ultraviolet spectra from the Hubble Space Telescope Cosmic Origins Spectrograph (HST COS) archive to locate intrinsic N V absorption systems. Our survey uncovered 59 intrinsic N V systems in the spectra of 428 low-redshift quasars, all found within the associated region (|Delta v|<5000 km/s). We consider the incidence of intrinsic absorbers as a function of quasar properties (optical, radio and X-ray). We find no intrinsic N V systems in the spectra of the radio-loud quasars, compared to 30% of the radio-quiet quasars containing at least one intrinsic system. Assuming intrinsic systems are equally likely to occur in radio-loud and radio-quiet quasars, there is a 0.5% probability of such a deficit occurring by chance in the radio-loud population. We propose that such a deficit of systems is caused by orientation effects: the available FIRST radio images show that 7 of the 10 radio-loud quasars have compact radio morphologies and a flat radio spectrum, implying that these quasars are face on, and that clouds that produce N V absorption are rarely found along the polar axis. In order to determine whether radio-loud quasars are devoid of N V systems, or if we were correct in that the likelihood of finding a N V systems is a function of inclination angle, more observations of steep-spectrum radio-loud quasars were needed. We used HST COS to obtain rest-frame UV spectra (1195 A-1250 A) of 13 low-redshift SDSS radio-loud quasars which show a wide range of FIRST morphologies to distinguish between these possibilities. Intrinsic N V absorption was detected in 6 of our 13 quasars. This suggests the lack of detections in the archival study was a result of an orientation effect/sampling bias rather than to differences in wind structure between radio-loud and radio-quiet quasars. We find significant overlap in radio core fractions between quasars with and without \ion{N}{5} detection. The quasars in our sample with N V detection span a range of inclination angles with respect to the polar axis from 20 degrees to >69 degrees while those without detected N V range from 15 degrees up to 61 degrees. A laminar outflow with a small opening angle would be difficult to explain given this overlap in radio core fractions. However, only 2 of the 15 systems found had inclination angles i<45 degrees. The remaining 13 N V absorption systems were found within the spectra of quasars at high inclination angles (i> 50 degrees). Additionally, each of the quasars with high inclination angles (i>50 degrees) that had N V absorption within its spectra were found to have multiple systems, indicating that such systems in high inclination angle quasars tend to cluster. This implies that the probability of finding an intrinsic \ion{N}{5} system within a radio-loud quasar increases as the inclination angle increases. Our observations suggest that a clumpy, sporadic outflow is the most likely explanation. Finally, we draw conclusions based on the results of the above findings. We also describe future work that can be done to advance our knowledge on this topic.