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Question: 1 what are the two main groups of galaxies on...

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1. What are the two main groups of galaxies on the Hubble Sequence? Give three distinguishing characteristics of each group and explain what causes their differing morphologies.


2a) What is a “rotation curve”, and what kind of galaxies can it be measured for?

b) What does the flatness of rotation curves at large radii indicate? Why did this come as a surprise when it was first discovered?

c) Show (with equations) how the rotation curve at large radius can be used to calculate the density of dark matter in the outskirts of a galaxy

d) You measure a 21 cm line spectrum for the nearby spiral galaxy NGC 7331 as shown, and you measure an integrated (extinction-corrected) B-band magnitude of 11.5. You also have a calibrated Tully-Fisher relation for B band, MB= −7.48 [log10(Vmax) − 2.5] − 19.55, where MB is the absolute B-band magnitude and Vmax is the maximum rotational velocity measured in km/s.

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