Testing the cosmological principle with CatWISE quasars: a bayesian analysis of the number-count dipole

Article Article scientifique Article Testing the cosmological principle with CatWISE quasars: a bayesian analysis of the number-count dipole eng 2023-08-01 2023-10-09 author Dam Lawrence 0000-0003-3163-9571 990293 Département de physique théorique (FITEO) author Lewis Geraint F. 0000-0003-3081-9319 author Brewer Brendon J. 231-245 10.1093/mnras/stad2322 0035-8711 https://academic.oup.com/mnras/article/525/1/231/7235095 <p>The Cosmological Principle, that the Universe is homogeneous and isotropic on sufficiently large scales, underpins the standard model of cosmology. However, a recent analysis of 1.36 million infrared-selected quasars has identified a significant tension in the amplitude of the number-count dipole compared to that derived from the cosmic microwave background (CMB), thus challenging the Cosmological Principle. Here, we present a Bayesian analysis of the same quasar sample, testing various hypotheses using the Bayesian evidence. We find unambiguous evidence for the presence of a dipole in the distribution of quasars with a direction that is consistent with the dipole identified in the CMB. However, the amplitude of the dipole is found to be 2.7 times larger than that expected from the conventional kinematic explanation of the CMB dipole, with a statistical significance of 5.7σ. To compare these results with theoretical expectations, we sharpen the ΛCDM predictions for the probability distribution of the amplitude, taking into account a number of observational and theoretical systematics. In particular, we show that the presence of the Galactic plane mask causes a considerable loss of dipole signal due to a leakage of power into higher multipoles, exacerbating the discrepancy in the amplitude. By contrast, we show using probabilistic arguments that the source evolution of quasars improves the discrepancy, but only mildly so. These results support the original findings of an anomalously large quasar dipole, independent of the statistical methodology used.</p> Quasars: general Galaxies: active Cosmic background radiation Cosmology: observations Large-scale structure of universe Dewey 500.2 37 Département de physique théorique 133 false Monthly notices of the Royal Astronomical Society 525 1 12fa92a4-edeb-4e05-b90f-41d67e12e657 Article (Published version) Public Article_scientifique_from_crossref.pdf 1561159 application/pdf CC BY-4.0 27aede3f5c6553f6ed114f9e9c065373955b987449a77cc7b4024f155e510748 openAccess Faculté des sciences / Section de physique / Département de physique théorique

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Testing the cosmological principle with CatWISE quasars: a bayesian analysis of the number-count dipole	Monthly notices of the Royal Astronomical Society			2023	56	284

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Dam, Lawrence