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Units of dex^-1

  1. Dec 11, 2009 #1

    I've come across a number density expressed in units of Mpc^-3 dex^-1; I understand the Mpc^-3 but not the dex^-1. I know dex is some kind of log scale with n dex = 10^n but I'm not sure what dex^-1 means and was wondering if anyone could help.

  2. jcsd
  3. Dec 14, 2009 #2
  4. Dec 14, 2009 #3


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    I got this from google (dex unit)

    a logarithmic unit being used in astronomy. Originally, dex was a convenient function defined by dex (x) = 10x. But the notation is now being used after the exponent in expressions such as -.043 dex, meaning 10-.043. Thus 1 dex equals a factor of 10, making the dex identical to the bel. The name "dex" is a contraction of "decimal exponent."
  5. Dec 14, 2009 #4
    Thanks - I'd found that same definition. But I'm still not 100% sure what the dex^-1 means. I mean, if 1 dex is 10 then maybe 1 dex^-1 is 0.1? But if it's just a constant factor of 0.1 to be applied to each data point then it seems pointless :confused:

    I've seen Mpc^-3 dex^-1 used in plots in papers so I was hoping it was a common definition that someone would be familiar with.
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