Problem Set #2

ASTR 3830

A                             B                                  C

D                              E                                  F

G                              H                                 I

1. Classify each of the nine galaxies shown above.
1. Estimate the inclination of the galaxy or explain why you can’t in each case.
1. In galaxy B above, you measure the Doppler shift of the 21 cm to be 60km/s at a point near the bottom of the image. Convert to estimated orbital velocity of the gas.
1. You observe some galaxy spectroscopically and determine its metallicity to be
–1.5.  What type of galaxy should you expect it to be, and why?
1. A generic galaxy rotation curve has the velocity rise linearly from 0 at the center to 200km/s at 5kpc from the center.  Then it remains constant at 200km/s out to 15kpc beyond which it can’t be measured. a) Make a plot of M(r), the total mass internal to the radius as a function of radius. Use grams for y coordinate.  b) Make a plot of the density of the dark matter in g/cc vs radius, assuming the dark matter is spherically symmetric.
1. For the same galaxy described in problem 5, estimate k/w as a function of radius, where k is the epicycle frequency and w is the orbit frequency.