Problem set due in class, Apr 09. Show your work, neatly.
1) Goto http://astro.princeton.edu/~frei/galaxy_catalog.html and classify, on the Hubble system, the following galaxes:
2) Using all the galaxies in http://astro.princeton.edu/~frei/galaxy_catalog.html use NED to find their B-V and U-B colors. Plot them using different symbols for ellipticals, spirals and irregulars.
3) If galaxies are composed on two populations (young and old), then we can estimate the change in color of the total galaxy as those two populations vary (assumingly from a pure old population = elliptical to a pure young population = irregular).
a) let the fraction of the young population be x, what is the fraction of the old population?
b) let L_V be the fraction of light in the V bandpass. What is the amount of light from the young population, L_Vy and the old population, L_Vo?
c) For a given color, B-V, what is the magnitude relationship between L_V and L_B?
d) For a young population with B-V=-0.2 and an old population of B-V=0.95, what is the relationship betweeen L_By and L_Vy? What is the relationship between L_Bo and L_Vo?
e) What is the relationship between L_By and the total amount of light at V, L_V? between L_Bo and L_V?
f) For a young population of U-B=-1.0 and an old population of U-B=0.6, plot on the same B-V vs U-B diagram as the data above, a locus of points for the fraction of values x=0, 0.2, 0.5, 0.7, 1.0. Comment on the locus compared to the real galaxy data and what this implies for galaxy stellar populations.