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Originally Posted by parejkoj
If I might interject for a moment...
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Yes please do.
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Not to be pedantic (though I suppose I am): what is the selection function for those galaxies? As I described above to Ari, it is possible to get a reduction in the number of sources at a given redshift, due to selection effects. Re-read my comments here for one example. Those comments were specifically for quasars, but there are similar problems when selecting galaxies for spectroscopy.
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As I understand it they combined together several catalogs to try an make a fully comprehensive sample as possible. I think that these catalogs all predate the use of fibers, so that is not an issue.
I do not deny that there will be selection effects. Why I claim is that selection effects will produce a smooth curve with a maximum of 2 or 3 inflections. They will not produce 7 evenly spaced peaks.
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What are the error bars on that graph? To roughly quote my advisor: "I won't do chi-by-eye without errorbars!" It looks to me like many of the "peaks" that you see are just statistical fluctuations. How did you draw the "smooth curve?" I don't recognize the function (too curvy for a log-normal), and it doesn't look like a chi-squared minimized fit to me. It looks like it runs too high above the data.
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There are no error bars, but in bins with 100, 400 or 1600 items the expected sampling errors amount to 1/10, 1/20, 1/40 of the numbers in the bins or 10, 20, 40. The early peaks are about 400/40 or 10 s.d. (where the data will be the best) and the later ones about 30/10 or 3 s.d. The result is very significant when all the data is taken together.
I simply drew a curve that follows the trend so that about equal amount of space shows between the curve and the line. Its shape is not important and even without it you can just test the difference between the peaks and troughs of the claimed 4330 km/s cycle.