Astr 222 Midterm Exam 2 Study Questions

Short Answer Questions

There will be 7 questions similar in style to the ones below; you pick 5 of them to answer.
Each question is worth 5 points.
Your answer should be a a few sentences / short paragraph long for each.
  1. Describe the general properties of starburst galaxies and explain how these starbursts might be triggered.
  2. Describe what we mean by the gas depletion time for galaxies, and how it differs between spiral galaxies and starburst galaxies.
  3. You are studying a galaxy cluster whose distance you have determined from its redshift, and you calculate a virial mass of 1015 Msun for it. How and why does your answer depend on the Hubble constant? If the Hubble constant was actually 20% larger than you thought, would your estimated mass get bigger, get smaller, or stay the same? Explain why.
  4. Describe the properties of radio galaxies, including the different sources of radio emission and an explanation of what's going on at the galaxy's center that powers all this emission.
  5. Describe the mass-metallicity relationship for galaxies, and how it explains the color trends of galaxies on the red sequence. Give a physical explanation for why the mass-metallicity relationship might exist.

Essay Questions

There will be 1 question, which will be taken from the list below.
The question is worth 15 points.
Your answer should be ~ 2-3 blue book pages long

  1. Describe the difference in physical properties between the inner and outer disks of spiral galaxies, and how this provides evidence for the idea of "inside-out galaxy formation." Make sure to explain what "inside-out galaxy formation" is!
  2. Sketch what the "central engine" of an AGN looks like. Use this sketch to explain how the "unified model" for AGN explain the differences seen in the spectra of Type I and Type II Seyferts. Explain how AGN might power radio galaxies, along with a plausible reason why radio galaxies are preferentially associated with elliptical galaxies.
  3. Describe the Tully-Fisher relationship and the Fundamental Plane. What quantities are involved, and what types of galaxies do they describe? How can they tell us about stellar populations and dark matter galaxies, and how can they be used to obtain distances to galaxies?
  4. Describe the properties of massive galaxy clusters: sizes, masses, galaxy types, gas content, etc. When we look at distant clusters, which we see as they were billions of years ago, the mix of galaxy types looks a bit different than in clusters today. Describe these differences, and explain the various processes which might have led to these changes in the galaxy populations over time.
  5. Explain why interacting galaxies form tidal tails, and why different interactions can give so widely varied shapes and properties for the tails. Explain also why galaxies merge, and what happens to the orbital energy and angular momentum the galaxies originally had.
  6. Describe the properties of spiral arms. Explain how density waves work, and how they solve the winding problem. Why would star formation occur preferentially in spiral arms?
  7. How do we measure the motions of gas and stars inside a spiral galaxy? How can we do it for elliptical galaxies? What do these measurements tell us about how V/sigma is different for spirals and for ellipticals (give characteristic values for V/sigma for each type of galaxy). Finally, describe the difference between pressure support vs rotational support to explain the flattening seen in some ellipticals. Which types of ellipticals can be explained by rotational vs pressure support?
  8. Describe how the merger of two spiral galaxies could produce an elliptical. Think both about the shapes of galaxies and how stars orbit inside them. Explain how a galaxy merger could transform some of the cold gas we see in spiral galaxy disks into the hot gas in an elliptical galaxy halo.


There will be 2 questions similar in style to the ones below.
Each question is worth 5 points.
Make sure to bring a stand-alone scientific calculator! No smartphones allowed.


You will get a page of equations and constants with the test, so you do not need to memorize constants or equations except for these:

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