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Journal-club Univers / Journal-club Universe

« Probing local isotropy with galaxy clusters »

Konstantinos Migkas
Astronomische Inst., Univ. Bonn (Bonn, Allemagne)

We use a novel method to test the local isotropy of the Universe using X-ray galaxy cluster observations. Specifically, we utilize the X-ray luminosity-temperature (Lx-T) scaling relation. While the temperature measurement does not depend on cosmology, the luminosity does, through the luminosity distance. Scanning the full extragalactic sky, we detect a region that seems to share a significantly different Lx-T relation than the rest of the sky. Many X-ray and cluster related reasons that could potentially explain this anisotropy were tested, but none was able to alleviate the tension. As more and more possible systematics are excluded, one can explain this anisotropy as an unexpectedly strong bulk flow motion, or even as local anisotropies in the expansion rate of the Universe. Future work in other wavelengths will help us pinpoint the reason behind this. No matter what the latter is, past X-ray cluster studies might need to consider how this effect would bias their results.
mardi 21 avril 2020 - 10:30
Webinaire, Institut d'Astrophysique
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