Selections from the following questions will compose about
70% of your midterm. While the
questions are generally of a qualitative nature, I expect your answers
to be complete and demonstrate an understanding of the underlying concepts.
Observational Measurements (1-2 questions from this set)
OM1. You observe a nearby star. How might you be able to directly determine its
distance?
OM2. What is a standard candle and why is it useful? Give two examples of
standard candles and explain how they work.
OM3. Discuss how velocities of stars or galaxies may be measured and the limitations
in determining the total velocities. What is meant by velocity dispersion?
OM4. You observe a sample of galaxies above a particular brightness. Comment
on the content of your sample in terms of the volume of the Universe
surveyed. Identify any biases in your sample. How might you correct for these biases?
OM5. What is meant by the term 'redshift'? How is the redshift of a galaxy
related to distance? Why is it dangerous to use redshifts to determine distance
for nearby galaxies?
OM6. What is meant by a Luminosity Function? What is it tracing and
why is it important that we define the luminosity function over all luminosities?
OM7. What is meant by "surface brightness" and why is it a useful quantity?
Define the terms 'scalelength' and 'effective radius'.
Spectra and Color(1 question from this set)
SS1. Explain how you can derive at least two different galaxy properties
from a galaxy spectrum.
SS2. Why does a spectral line in a galaxy have a width associated with
it?
SS3. What is the relationship between galaxy type, galaxy color,
and emission/absorption lines in a galaxy spectrum? Contrast the colors and
spectral features for typical spiral and elliptical galaxies.
Galaxy Properties (3-4 questions)
G1. Explain why stars in galaxies are mostly red, cool,
main-sequence stars.
G2. Describe the Hubble Classification system and its limitations
in grouping galaxies by similar physical characteristics.
G3. Summarize Hubble's three criteria for classifying spiral
subtypes, going from left to right in the tuning fork diagram.
Which of these criteria traces a physical property of the galaxy
best and why? Why might the other two criteria be misleading?
G4. What is meant by the Morphology-Density Relationship?
G5. Describe the types of galaxies found in the Local Group. What type of
galaxy is most populous in the Local Group?
G6. What does the distribution of galaxies look like within 1 billion light years?
What is meant by the term "supercluster"?
G7. Contrast the surface brightness profiles of a typical elliptical and
a typical spiral galaxy. What is meant by the Sersic index? What Sersic index (indices)
are typical of spirals? of ellipticals?
G8. What galaxy properties are correlated in the
Tully-Fisher and Faber-Jackson relations? Why are these relations
surprising, given what you know about the behavior of light and mass
in galaxies? Give another reason why these relations are so useful
(besides what they reveal about galaxy formation and evolution).
G9. Describe how you can determine whether a galaxy is dominated by random
or rotational motions. What types of galaxies are dominated by random motions? by
rotational motions?
G10. What is the Fundamental Plane and what does it tell us? Give two examples
of relationships that are projections of the Fundamental Plane.
G11. What is the Virial Theorem and what does it mean to say that a system is
"virialized"? How could you estimate whether a system is virialized?
G12. Describe the three types of ellipitical populations. What properties do these
types have in common? Do any have similar properties to spirals?
G13. What is the difference between core and power-law ellipticals? How else
do these types contrast?
GR14. What does a color-magnitude diagram of galaxies trace? Provide
a schematic color-magnitude diagram, indicating the names and locations
of the two main regions populated by galaxies. What is the name of the
relatively unpopulated region between the more populated
region? Describe the characteristics of galaxies in each of these three regions.
Mass and Dark Matter (1 question)
M1. Derive a formula for the orbital velocities as a function of radius
for the planets around the Sun, assuming the orbits are circular.
How will the formula change for the orbit of a star around the center of a
galaxy? Be sure to justify why you can apply this formula to an extended
mass distribution.
M2. Discuss the observational evidence for dark matter in an
elliptical galaxy. Outline how
the mass of an elliptical galaxy can be estimated.
Can the total mass of an elliptical galaxy
be determined, based on available observations?
M3. Discuss the observational evidence for dark matter in a
spiral galaxy. Outline how
the mass of a spiral galaxy can be estimated. Can the total mass of
a spiral galaxy be determined, based on available observations?
M4. Show that observed galaxy rotation curves are consistent with
a density of the dark matter halo which depends on radius
as r-2.
M5. What is meant by "mass-to-light" ratio? What is the mass-to-light ratio
for a typical stellar population? How does this compare to the measured mass-to-light
ratios for galaxies?
Last updated: January 31, 2019