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Homework Help: Surface brightness and effective radius

  1. Feb 9, 2016 #1
    1. The problem statement, all variables and given/known data
    Assuming that the average surface brightness within the effective radius is 19 mag/arcsec2, use the definition of the effective radius to estimate what the effective radius in kpc would be for NGC 4216 if it was an elliptical galaxy.

    2. Relevant equations
    All the logs are base 10

    log(i(r)/ie)= -3.3307 [(r/re)^1/4-1]

    3. The attempt at a solution
    I am given ie in the problem which is 19. I tried to find i(r) using i(r)=apparent magnitude+2.5log(surface area) but that gives me a negative i(r) which does not make sense and gives me log of a negative value which does not exist.

    Can you tell me what I need to do, not necessarily the answer but values i could use or i need to find to get this.

    Thank you.
  2. jcsd
  3. Feb 14, 2016 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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