r/cosmology • u/ThickTarget • 11d ago
Kilo-Degree Survey Confirms Standard Model of Cosmology - Cosmic Shear Results from the Full KiDS Survey
https://news.rub.de/english/press-releases/2025-03-26-astrophysics-kilo-degree-survey-confirms-standard-model-cosmology9
u/castin 11d ago
Considering that DES-Y3 data sees an S8 tension with much larger sky coverage than KiDS, it's surprising that this new result is driven so much by higher statistics (+improved redshifts, etc). Then again, it looks like KiDS has a higher galaxy density so that could also be playing a role here too. Very interested in what LSST sees!
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u/ThickTarget 10d ago
Catherine Heymans commented on bluesky that the spectroscopic calibration and simulations pushed them up by ~1.5 sigma, the rest was from the area. That does seem to indicate it's not purely statistical, and is more systematic, in the case of KiDS anyway.
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u/justgivemeauser123 11d ago
Nowadays I take any deviation form S8 with grain of salt. I have been through tons of these papers and tons of talks. But somehow I am still skeptical of the error bars they produce. Recently I was at a talk claiming S8 deviations using DESI. They did blind analysis and what not but at the end of the day looking at their graphs, I would call it "barely" an evidence if at all. At this point it seems more of a hype thing. I have been told there have been way more convincing "evidence" that eventually bit the dust.
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u/ThickTarget 11d ago edited 11d ago
There was a lot of excitement last week with the ACT and DESI results, and also the first surge of papers from Euclid. The results from the completed KiDS haven't yet made a big splash in the media, but they are very interesting. The headline result is that the tension between weak lensing results and the CMB for measuring the clumpiness of matter (sigma_8 or S_8) has gone away. This tension was seen in lots of weak lensing surveys (e.g. CFHTLens, DES, HSC, early KiDS) but now seems to have gone away was the full area of the completed survey. I've read elsewhere that extra simulations and much expanded spectroscopic calibrations drove the constraint up to meet the CMB expectation. You might ask if there could be room for human bias in analyzing data like this, and tweaking things until it matches. Like previous KiDS results the analysis was done blind, only at the very end did the team know the true result.
I posted the press release for general readability. The KiDS webpage has lots of extra links. There is also an hour-long talk on the results on YouTube.. I'll link the papers below.
arXiv: KiDS-Legacy: Cosmological constraints from cosmic shear with the complete Kilo-Degree Survey
arxiv: The fifth data release of the Kilo Degree Survey: Multi-epoch optical/NIR imaging covering wide and legacy-calibration fields
arxiv: KiDS-Legacy: Consistency of cosmic shear measurements and joint cosmological constraints with external probes
arxiv: KiDS-Legacy: Redshift distributions and their calibration
arxiv: KiDS-Legacy: Covariance validation and the unified OneCovariance framework for projected large-scale structure observables
A lot of theory papers have been written about this tension, but the observational significance has always been low. I wouldn't take this as the final result that there is no tension, there are still other surveys finding results with are further from the Planck CMB result. In the next few years we will see the first results from Euclid, which should offer improved systematics and statistics for weak lensing.