Review Questions

1. What quantitatively defines whether an ion is a "low-ionization" ion. Construct a list the commonly observed ions and their transitions that are discussed in this chapter. (Don't forget SiII!)

2. Describe the currently measured redshift evolution of the mass density of MgII absorbers (ΩMgII). Over what redshifts is this measurement most uncertain and why? What are the astrophysical expectations for the evolution of ΩMgII from z = 7 to z = 0?

3. For MgII absorbers, compare and contrast the evolution of dN/dX in each of the four equivalent width bins, Wr < 0.3 Å, 0.3 ≤ Wr < 0.6 Å, 0.6 ≤ Wr < 1.0 Å, Wr ≥ 1.0 Å. What is a currently accepted astrophysical interpretation for the redshift evolution of the Wr ≥ 1.0 Å absorbers. 

4. In Equation 8.5, what is the parameter ε designed to measure ? What does a positive or negative value of ε implicate?

5. What is the MgII forest (if it exists)? Can you think of some astrophysically important implications about galaxy evolution and IGM metal enrichment evolution that can be inferred or learned from the measured characteristic properties of a MgII forest? 

6. Briefly describe why it is believed there may be two-populations of CaII absorbers? Between 0 ≤ z ≤ 2, do CaII absorbers show evidence for evolving or not evolving? Comparing the redshift path number density of CaII and MgII absorbers, for every 100 MgII absorbers, how many of these would be expected to also exhibit CaII absorption?

7. For what reasons do we expect that NaI absorbers almost exclusively arise in very high HI column density absorbers? What can the ratio of the NaI/CaII column densities tell us about the gaseous absorbing medium (two things).

8. What is generally known about NaI absorbers in intervening DLAs? What is generally known about NaI absorbers viewed down-the-barrel in starburst galaxies? 

9. Explain why the redshift path visibility of OI 1302 absorption is confined to relatively small redshift intervals and (given current instrumentation) primarily at z ≈ 0 and high redshifts (z ≥ 2.5).  

10. Describe the general trend in the redshift evolution of dN/dX for OI for 2.4 ≤ z ≤ 7. Over this redshift range, is this trend favored to be an increase or decrease in the ionization of the gas or an increase or decrease in the evolution of the abundance of oxygen?

11. Briefly describe the general inferred properties of clouds that give rise to CI absorption and what other type of absorption (molecular, atomic, excited states. etc) is seen in CI selected absorbers. What evidence do we have that the CI gas is embedded in dynamically active neutral and low ionization gas structures?

12.  Describe the observed evolution of dN/dX of CI absorbers. Comparing to the redshift path density of DLAs at z ≈ 2.5, for every 100 DLAs seen in absorption in how many would have associated CI absorption be expected?

13. Describe the high redshift (z > 5) observed evolution of dN/dX of CII and SiII absorbers. Compare and contrast it to the OI evolution (are their trends with redshift consistent with or different than OI evolution?).

14. Describe how the ratio of the CII to CIV column densities evolves for z > 5.  Why is MgII a good proxy for the CII values? At what redshift does there appear to be a dramatic change in the CII/CIV ratio? What is/are the astrophysical interpretation(s) of this evolution. 

Problems

1. Under construction