Review Questions

1. In 1970 John Bahcall proposed two classes of absorption lines.  What is each population called and how is each of these populations defined?

2. What was the January 1965 paper by Scheuer about and what three possible conclusions did he draw? Similarly, what was the May 1965 paper by Gunn & Peterson about?  What did it predict?

3. What absorption features are the quasars PHL 5200 and RS 23 famous for?  What are these absorption features called today? HINT: they are also known by a three letter acronym.

4. Qualitatively (in words), what does the quantity dN/dz measure? When we say the phrase “non-evolving population,” what physical quantities are we saying are not evolving (staying constant)?

5. What years did the IUE launch and how long was it operational? Describe what electromagnetic window it opened and describe its instruments and their capabilities.

6. What was the HST Quasar Absorption Lines Key Project? Describe a few main accomplishments of this project.

7. What is the FOS instrument, when was/is it operational, and what are its capabilities?  What is the GHRS instrument, when was/is it operational and what are its capabilities? What is the STIS instrument, when was/is it operational and what are its capabilities? What is the COS instrument, when was/is it operational and what are its capabilities?

8. What are the capabilities of HIRES and UVES that make them so powerful for the study of quasar absorption lines? 

9. Though the instrument is not discussed in Chapter 1, what is the X-shooter instrument and what makes it so powerful for the study of quasar absorption lines?

Problems

1. For the z = 2.41 quasar illustrated in Figure 1.1, over what observed wavelengths would you expect to see IGM/CGM Ly⍺ lines (HI 1215) from the Ly⍺ forest that are “clean,” meaning there are no IGM/CGM Lyβ lines in that wavelength range. Over what observed wavelength range would you expect to see CIV 1548 absorption that is not contaminated by IGM/CGM Ly⍺ lines.

2. Starting with Equation 1.2, if the deceleration parameter, q0, is equal to ½, write down the simplified expression for dN/dz for a non-evolving population. Given this expression, if you measure 10 absorbers at <z> = 1, how many would you expect to measure at <z> = 3?

3. Starting with Equations 1.3 and 1.4, let's say you measure the relative flux at the Lyman break (912 Å) to be f / f0 = 0.1. What is the neutral hydrogen column density of the absorbing gas? Be sure to provide the units.