Review Questions

1. Compare and contrast the observed defining characteristic properties of BAL and NAL absorption.  

2. What does QPQ stand for?

3. Describe the balnicity index (BI) and how it is computed. Later, the absorption index (AI) was introduced. How does the definition of AI differ from BI and what perceived short comings of the BI is AI designed to remedy?

4. A great deal of effort has gone into determining the BAL quasar fraction, i.e., the fraction of quasars that exhibit BAL absorption. What are some implications for the nature of quasars if the BAL fraction were observed to evolve with redshift? Describe the current results of such studies.

5. Compare and contrast the five main subclasses of BAL quasars: HiBAL, LoBAL, FeLoBAL, mini-HiBAL, and mini-LoBAL.

6. For what scientific reasons is it important to fully characterize the variability of BAL absorption across all subclasses of BAL quasars? In other words, what are some of the priority science motives and questions being investigated?

7. Why is there no index for characterizing NAL absorption? In other words, why is it difficult to determine if a narrow absorption line is in fact NAL absorption associated with the quasar itself? 

8. What are the three main criteria by which NALs are identified in quasar spectra? Briefly describe each, mentioning its merits for identifying NALs, but also its possible shortcomings and the ambiguities it faces.  

9. Combining the NAL classification schemes of Misawa et al (2007), Muzahid et al. (2013), and Culliton et al. (2019) yields four classes of NALs, some with refined subclassifications.  In your own words, briefly describe each of these classes and their subclasses.

10. Briefly describe what is known about (i) NAL variability or lack thereof, (ii) the simultaneous occurrence of NALs and BALs, and (iii) some proposed scenarios for the physical origin of NAL absorption.

11. In your own words, describe what line locking is and describe its spectral signature (what absorption patterns to look for in the spectra). Does line locking occur only in fine-structure doublets, or can lines from different ions partake in line locking? How common is line locking (what fraction of NAL quasars exhibit the phenomenon)?  Is line locking a short transient phenomena, or can it be stable? 

12. What is the "longitudinal" proximity effect? Briefly describe up to three methods for measuring the longitudinal proximity effect. What astrophysical insights does the measurement provide?

13. Summarize the general observational findings of QPQ studies, including findings on the "transverse" proximity effect. What do we infer about the influence of the central engine as a source of ionizing photons in the CGM of quasars? What are the astrophysical ambiguities when it comes to interpreting the data on the CGM of quasars?

Problems

1. Under construction