Understanding Units of dex^-1 in Number Density Measurements

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Discussion Overview

The discussion revolves around the interpretation of the units Mpc^-3 dex^-1 in the context of number density measurements, particularly in astronomy. Participants seek to clarify the meaning of the dex^-1 component and its implications for data representation.

Discussion Character

  • Conceptual clarification, Exploratory

Main Points Raised

  • One participant expresses confusion about the meaning of dex^-1, noting that while they understand Mpc^-3, the logarithmic nature of dex is unclear.
  • Another participant provides a link to a source that uses the term Mpc^-3 dex^-1 in the context of luminosity functions, suggesting it is a recognized unit in the field.
  • A third participant offers a definition of dex as a logarithmic unit, explaining its relationship to factors of 10, but does not clarify its application in the context of dex^-1.
  • The original poster questions whether dex^-1 could imply a constant factor of 0.1, but finds this interpretation potentially unhelpful, indicating uncertainty about its practical significance in data analysis.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the meaning of dex^-1, with multiple interpretations and uncertainties expressed regarding its application in number density measurements.

Contextual Notes

Participants note the lack of clarity around the implications of dex^-1 and its role in data representation, indicating that further exploration or clarification may be necessary.

v0lD
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Hi,

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.

Thanks!
 
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I got this from google (dex unit)


dex
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."
 
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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