# Astr/Phys 328/428 Midterm Exam Questions (2016 edition)

There will be 3-4 questions taken from this list. You should plan on spending ~ 2-3 bluebook pages answering each one. Any sketches you draw should have labeled axes, with meaningful scales. Any numbers you give should be "ballpark correct." Any equation you use must have terms described.
1. Why do we need to study relatively distant galaxies to get a get a measure of the Hubble constant? Why can't we just use distances to nearby galaxies, where Cepheids give us good distances, to measure H0? Why are Cepheid distances so important for measuring H0?
2. Describe several reasons (both physical and observational) why high redshift galaxies might look different from galaxies in the local universe.
3. Describe the "surface brightness fluctuation" technique for finding distances to galaxies. What data do you need? Is this technique better for spirals or ellipticals? Why?
4. Write down the Friedmann equation, and describe each term. Using the Friedmann equation, derive expressions for the following for an Omega=1, Lambda=0 universe:
• R(t)
• t(z)
• the current age of the Universe
5. Explain the supernova cosmology project, the cosmological test it is making, and the recent results from this project.
6. Explain and compare the two galaxy dynamical distance indicators. What galaxies do they work on? What are the advantages and disadvantages to each one?
7. Describe what we mean by "peaks" in the power spectrum of the microwave background. What causes these peaks, and what do they tell us about the Universe?
8. Describe the Sunyaev-Zeldovich Effect, and how we can use it to constrain cosmological parameters. What data is needed for this test?
9. Describe the process of Big Bang Nucleosynthesis and how it can constrain the baryon fraction of the universe. What value for OmegaB is indicated by BBN?
10. Describe the Tully-Fisher relationship, and show mathematically how it implies a strong connection between dark matter and stars inside a galaxy. Discuss the data you need to measure H0 with Tully-Fisher.
11. Briefly describe the importance of the six foundations of modern cosmology.
12. Explain what a K-correction is and what it depends on. Explain qualitatively how a K-correction for an elliptical galaxy would be different from a K-correction for an actively star-forming spiral galaxy.
13. Why is the surface brightness of a galaxy independent of distance in the nearby universe, but a strongly decreasing function of redshift at cosmological distances?
14. How do we measure the primordial abundances of the light elements and what does they tell us about the cosmological parameters?
15. On one plot, sketch R(t) for the following cosmologies, and for each case, describe why the curve has the shape it does:
• H0=70, OM=0, OL=0
• H0=70, OM=1, OL=0
• H0=70, OM=0.3, OL=0
• H0=70, OM=0.3, OL=0.7
• H0=50, OM=0.3, OL=0.7