What is the ugriz magnitude system?

  • While studying photometric redshifts, I came across the ugriz (or u'g'r'i'z) system for classifying magnitudes of galaxies, but I didn't find much information on the internet about how it works.



    Can somebody explain that? Do the letters "ugriz" have any special meaning, or is its just a nomenclature?


  • HDE 226868

    HDE 226868 Correct answer

    5 years ago

    "ugriz" is short for U-band, G-band, R-band, I-band, and Z-band, detailed on the Wikipedia article on photometric systems:
    $$\begin{array}{|c|c|}
    \hline \text{Band}&\text{Effective Wavelength Midpoint }(\lambda_{\text{eff}})\\
    \hline \text{U} & \text{365 nm}\\
    \hline \text{G} & \sim\text{475 nm}\\
    \hline \text{R} & \text{658 nm}\\
    \hline \text{I} & \text{806 nm}\\
    \hline \text{Z} & \text{900 nm}\\
    \hline
    \end{array}$$
    This $ugriz$ system is slightly different from the $u'g'r'i'z'$ system; conversions can be found here. The starting point is the same (note that $u(\text{2.5m})=u'$), but there are slight vertical and horizontal shifts.



    The differences between $ugriz$ and $u'g'r'i'z'$ are much smaller than the differences between $u'g'r'i'z'$ and the $UBV(RI)_C$ system, which was replaced by them both. This older system of filters had large overlaps and did not cover as broad a range. See Fig. 1 from this thesis for a comparison:



    enter image description here


    I think its worth pointing out that ugriz and u'g'r'i'z' are two different, but similar systems.

    @zephyr Very good point. Done.

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Content dated before 7/24/2021 11:53 AM