Can the Dark-Matter Deficit in the High-Redshift Galaxies Explain the Persistent Discrepancy in Hubble Constants?

Abstract

One of hot topics in the last years is a systematic discrepancy in the determination of Hubble parameter by various methods. Namely, the values derived "directly" from the distance scale based on Cepheids and supernovae-and referring to the relatively "local" part of the Universe-are about 10% greater than the ones following from the analysis of the cosmic microwave background (CMB) radiation, which refers to the "global" scales. The most popular interpretation of this discord, widely discussed nowadays, is variation of the dark-energy equation-of-state parameter w. However, there might be a much simpler explanation, following from the recent observations of the rotation curves in the high-redshift galaxies. Namely, it was found that they have much smaller dark-matter halos than galaxies in the vicinity of us [Genzel, et al. Nature 543 (2017), 397]. Since both the dark and luminous matter possess the same dust-like equation of state and, therefore, their average cosmological densities evolve by the same way, our local neighborhood is not quite typical but rather overfilled with the dark matter. Then, the local value of the Hubble constant should be greater than the global one. Roughly speaking, a twofold excess of the dark matter in our local Universe would give just the above-mentioned 10% increase in the value of Hubble parameter.