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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 s1 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 TullyFisher
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 Bmag
arcsec2? BIG HINT: W...
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This document was uploaded on 03/04/2014 for the course ASTROPHYS 362 at Minnesota State University Moorhead .
 Spring '14
 Dr.JuanCabanela

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