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Hint surface brightness is the flux per solid angle a

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Unformatted text preview: the observed light), show that the surface brightness of a galaxy is independent of its distance from the observer. HINT: Surface brightness is the flux per solid angle. A solid angle is defined as the surface area subtended by the solid angle divided by the distance squared (such that for a sphere the surface area 4πd2 divided by d2 gives 4π steradian total solid angle). 4. [C&O 25.8 (tweaked)] NGC 2639 is an Sa galaxy with a measured maximum rotational velocity of 324 km s-1 and an apparent magnitude of B = 12.22 mag (after making corrections for Galactic extinction). a. Estimate its absolute magnitude in the B band from the Tully-Fisher relation. b. Determine the distance to NGC 2639 using its distance modulus. c. What is the galaxy's radius (R25) at a surface brightness level of 25 B-mag arcsec-2? BIG HINT: W...
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