Review Questions

1. What is the significance of the 1969 paper by Bahcall & Spitzer entitled "Absorption Lines Produced by Galactic Halos? What hypothesis was required about galaxy halos and what forced that deduction?

2. The opening statement of this chapter is that it took three and a half decades for astronomers to firmly establish that galaxies have dynamically bound extended gaseous halos. (i) For MgII absorption, provide a brief accounting of this scientific journey from the mid-1970s to the mid-1990s. (ii)  Do the same for Ly⍺ and DLA absorption from the mid-1990s to the mid-2000s. (iii)  Do the same for CIV and OVI absorption.  In your accountings, identify and incorporate the seminal studies and what they discovered. 

3. In your own words, define and describe the "baryon cycle." List each of the eight components of the baryon cycle (as illustrated in Figure 12.3) and describe their role (contributing impact on the galactic evolutionary process).  

4. What is cold-mode accretion?  What is hot-mode accretion? Which mode is expected to most directly fuel star formation? Why? Describe the predicted galaxy mass dependence of cold-mode and hot-mode accretion as a function of redshift. 

5. In the context of the baryon cycle, what is stellar feedback? AGN feedback? What roles do stellar and AGN feedback play in governing the stellar formation properties of galaxies? Describe the generally adopted scenario of how the dominant mode of feedback changes as a function of halo mass. 

6. In the NFW dark matter density profile, what are (list and define) the three parameters that fully describe a dark matter halo density profile? 

7. Qualitatively, in words, what is the definition of the virial radius and how does the factor ∆c dictate its enclosed spherical volume?  

8. Describe the role of dark matter halos in governing the physical processes of baryonic gas and in the development and evolution of galaxies of various masses.

9. In words, what is the halo mass function (HMF)?  What is the stellar-halo mass relation (SHMR), which is sometimes referred to as the stellar-mass to halo-mass (SMHM) function?

10. Consider Figure 12.6. Describe what relations this diagram is showing and explain what we learn astrophysically about galaxies in dark matter halos from these relations.

11. Figure 12.6 applies for z = 0. Consider Figure 12.5(e,f).  (i) What is galaxy upsizing?  (ii) What is galaxy downsizing? (iii) Describe the upshot of what these curves are telling us in terms of galaxy upsizing/downsizing as a function of redshift for "low mass halos" and for "high mass halos."  (Which mass regime is downsizing and which mass regime is upsizing?)

12. What is halo abundance matching (HAM) and what is its utility? Qualitatively describe how, in practice, one implements HAM?

13. Hydrodynamic cosmological simulations of galaxies are constrained by observations. Indeed to be "fully" successful, simulations need to pass "two tests." (i) Describe "Test 1". (ii) Describe "Test 2". (iii) What are the challenges for a simulation to pass both tests simultaneously?

14. Consider Figure 12.8. Based on the general findings of simulations like these, briefly summarize the halo mass dependencies of the CGM. How does this dependence compare with the scenarios of cold-mode and hot-mode accretion? Also, briefly summarize the feedback dependencies of the CGM. 

15. Qualitatively describe the modern composite model of the CGM.  That is, what are the (currently adopted) dominant spatial-kinematic components of the CGM of a "normal" galaxy?

16. Why do we say that our model of the CGM is a composite model?

Problems

1. Under construction