Review Questions

1. What quantitatively defines whether an ion is an "intermediate ionization" ion. Construct a list the commonly observed ions and their transitions that are discussed in this chapter. 

2. Consider the measured properties of CIV absorbers, which include (i) the redshift path densities (dN/dz and dN/dX), (ii) the two-point velocity correlation function (TPCF), (iii) the column density distribution function (CDDF), (iv) the SiIV/CIV column density ratio, (v) the mass density (ΩCIV), and (vi) the carbon abundance [C/H]. Briefly describe the redshift evolution of each of these quantities and, for each, provide at least one astrophysical insight gained from the measured evolution. [Note: For (iv), this ratio is also discussed from the perspective of SiIV-selected absorbers- see review question 4.]

3. Describe the pixel optical depth (POD) method developed in the mid-1990s. What was found for CIV and SiIV absorbers using POD methods and what are the inferred astrophysical implications?  What is super-POD and how does it differ from "regular" POD.  

4. Consider Figure 9.14. Describe what this figure shows is occurring with CIV and SiIV absorbers.  What is it teaching us about the astrophysics of the higher redshift Universe? 

5. Briefly describe the tension between the measure dN/dX of CIV and SiIV absorbers and theoretical predictions of these quantities based on simulations.  What are some possible (physics/computational) challenges faced by the simulators?

6. CIII-selected absorbers at low (z < 1) and high (z > 2) redshift appear to behave as if they are two different populations of absorbing structures. Briefly compare and contrast the multiple differences in physical properties of CIII absorbers at low and high redshift.

7. Why have SiIII-selected absorbers studied for z < 1 only? What is the evidence that SiIII does not strictly trace SiII absorption nor strictly trace SiIV absorption.  What is the interpretation of that evidence?

Problems

1. Under construction