Understanding Units of dex^-1 in Number Density Measurements

[v0lD]

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!

 

[v0lD]

If it helps the number density appears here (at the bottom of the section):

http://www.ias.u-psud.fr/irgalaxies/model.php#IDLSaveSets

"Luminosity Functions of normal galaxies, starburst galaxies, and total galaxies, in units of Mpc-3 dex-1."

 

[mathman]

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."

 

[v0lD]

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

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.