Given an image of a disk galaxy, you have measured that the average surface brightness at two radii (R = R1 and R = R2) are I1 and I2 respectively. The disk surface brightness profile has the exponential form of I(R) = I0 e(-R/Rd). What are the values of I0 and Rd for this disk?

On a 1-to-10^19 scale our Milky Way galaxy would just about fit on a soccer field. On this scale, how far is the distance from the sun to alpha centauri (one of the closest stars to the sun, at a distance of 4.4 light years).

A galaxy's rotation curve is a measure of the orbital speed of stars as a function of distance from the galaxy's centre. The fact that rotation curves are primarily flat at large galactocen- tric distances (vrot(r) ~ constant) is the most common example of why astronomer's believe dark matter exists. Let's work out why! Assuming that each star in a given galaxy has a circular orbit, we know that the accelera- tion due to gravity felt by each star is due to the mass enclosed within its orbital radius r and equal to v?/r. Here, ve is the circular orbit velocity of the star. (a) Show that the expected relationship between ve and r due to the stellar halo (p(r) xr-3.5) does not produce a flat rotation curve. (b) Show that a p(r) ∞ r¯² density profile successfully produces a flat ro- tation curve and must therefore be the general profile that dark matter follows in our galaxy.

Figure 2 shows the "rotation curve" of NGC 2742. It plots the “radial velocity (V)" (how fast material is moving either toward or away from us) that is measured for objects at different distances (R = radius") from the center of the galaxy. The center of the galaxy is at 0 kpc (kiloparsecs) with a speed of 9 km/sec away from us. (These velocities have been corrected for the observed tilt of the galaxy and represent true orbital velocities of the stars and gas.) 200 100 U4779 -100 As you can see, one side of the galaxy is moving with a negative velocity (spinning toward us), while the other side has a positive velocity (spinning away from us). Using Newton's gravity equation, we will be able to determine the gravitational mass of the entire galaxy and how the mass varies versus distance from the galaxy's center. -200 -8 8 -4 Radius (kpc) Read the following text carefully and follow the instructions: Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should…

what is the difference between an E0 galaxy and an E1 galaxy?

9

If a quasar is 2,000 times more luminous than an entire galaxy, what is the absolute magnitude of such a quasar?  Note: The absolute magnitude of the Milky Way Galaxy is about −21. Hint: Use the formula for magnitudes and flux ratios,

If a galaxy contains a supernova that at its brightest has an apparent magnitude of 16, how far away is the galaxy? Assume that the absolute magnitude of the supernova is −18. (Hint: Use the magnitude-distance formula d = 10(mV − MV + 5)/5.)

The hydrogen Balmer line has a wavelength of 486.1 nm. It is shifted to 565 nm in a galaxy's spectrum. What is the radial velocity (in km/s) of the galaxy? (Indicate the direction with the sign of your answer.)