Theoretical systematics in testing the Cosmological Principle with the kinematic quasar dipole

Abstract

The Cosmological Principle is part of the foundation that underpins the standard model of the Universe. In the era of precision cosmology, when stress tests of the standard model are uncovering various tensions and possible anomalies, it is critical to check the viability of this principle. A key test is the consistency between the kinematic dipoles of the cosmic microwave background and of the large-scale matter distribution. Results using radio continuum and quasar samples indicate a rough agreement in the directions of the two dipoles, but a larger than expected amplitude of the matter dipole. The resulting tension with the radiation dipole has been estimated at $\sim 5\sigma$ for some cases, suggesting a potential new cosmological tension and a possible violation of the CP. However, the standard formalism for predicting the dipole in the two-dimensional projection of sources overlooks possible evolution effects in the luminosity function. In fact, radial information from the luminosity function is necessary for a correct projection of the three-dimensional source distribution. Using a variety of current models of the quasar luminosity function, we show that neglecting redshift evolution can significantly overestimate the relative velocity amplitude. While the models we investigate are consistent with each other and with current data, the dipole derived from these, which depends on derivatives of the luminosity function, can disagree by more than $3\sigma$. This theoretical systematic bias needs to be resolved before robust conclusions can be made about a new cosmic tension.

13 pages, 3 figures, 2 tables. Version published in The Astrophysical Journal

References in corpus (6)

• Array Programming with NumPy
• A Challenge to the Standard Cosmological Model
• Dipoles in the Sky
• A new way to test the Cosmological Principle: measuring our peculiar velocity and the large scale anisotropy independently
• The kinematic dipole in galaxy redshift surveys
• Probing statistical isotropy of cosmological radio sources using SKA

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• Cosmological foundations revisited with Pantheon+
• Reassessment of the dipole in the distribution of quasars on the sky
• Tomographic redshift dipole: Testing the cosmological principle
• Some disquisitions on cosmological 2-form dualities
• The kinematic contribution to the cosmic number count dipole
• The low multipoles in the Pantheon+SH0ES data
• Cosmic topology. Part IIIa. Microwave background parity violation without parity-violating microphysics
• An Independent Measure of the Kinematic Dipole from SDSS
• Combining chirp mass, luminosity distance and sky localisation from gravitational wave events to detect the cosmic dipole
• Using relativistic effects in large-scale structure to constrain astrophysical properties of galaxy populations
• Measuring our peculiar velocity from spectroscopic redshift surveys
• Matter Dipole and Hubble Tension due to Large Wavelength Perturbations
• Fast and spurious: a robust determination of our peculiar velocity with future galaxy surveys
• The Ellis and Baldwin test of the Cosmic Dipole: Exploring the impact of multiple flux density cuts
• Cosmic Dipoles from Large-Scale Structure Surveys