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As we all know, the distribution of galaxies, which depend on the spatial coordinates, can help us understand the large-scale structure of the Universe. We can measure the distribution of galaxies from the Sky Survey Project directly, or examine it from the Hydro/N-body simulations.

My question is that if there are any observables that just depend on the distance to us, i.e. the scale. If so, such observables are one-dimensional.

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    $\begingroup$ The Lyman α forest? $\endgroup$
    – pela
    Jul 11 '21 at 22:40
  • $\begingroup$ @pela Are there any others? $\endgroup$
    – Wang Yun
    Jul 12 '21 at 0:39
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    $\begingroup$ I am not sure if this matches your criteria, but the frequency dispersion (1, 2, 3, 4) of Fast Radio Bursts or FRB's depends on distance, and is used as a measure of that distance. Right now statistics are very low so it would probably not be useful to show clustering. $\endgroup$
    – uhoh
    Jul 12 '21 at 1:50
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    $\begingroup$ You could also consider looking for other absorbers in background spectra than just the Lya forest, e.g. DLAs. But these are rare enough that you typically only get one or two, so could hardly be called "clustering analysis". Most lines of sight through the Universe contain only one or a few galaxies. If you want to study clustering, you need to have enough clustering objects to study. In a 1D line of sight, that basically restricts you to diffuse intergalactic gas clouds, i.e. the Lya forest. $\endgroup$
    – pela
    Jul 20 '21 at 12:35
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    $\begingroup$ But with many adjacent 1D lines of sight, such as offered by integral field spectroscopy, you can study galaxy clustering (see e.g. the recent paper by Herrero Alonso et al. (2021)). $\endgroup$
    – pela
    Jul 20 '21 at 12:37

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