Discord in Concordance Cosmology and Anomalously Massive Early Galaxies

TL;DR

This paper discusses discrepancies in cosmological parameters derived from different observations, highlighting tensions between CMB data and non-CMB measurements, and explores how massive early galaxies might influence these tensions.

Contribution

It identifies potential systematic effects in CMB analysis at small scales and links these to the unexpected abundance of massive high-redshift galaxies, proposing a possible explanation for the Hubble tension.

Findings

Good agreement on H0 and Omega_m from non-CMB data

Tension between Planck and WMAP3 cosmologies

Massive high-redshift galaxies may affect CMB lensing and parameter estimates

Abstract

Cosmological parameters are constrained by a wide variety of observations. We examine the concordance diagram for modern measurements of the Hubble constant, the shape parameter from large scale structure, the cluster baryon fraction, and the age of the universe, all from non-CMB data. There is good agreement for $H_0 = 73.24 \pm 0.38\;\mathrm{km}\,\mathrm{s}^{-1}\,\mathrm{Mpc}^{-1}$ and $\Omega_m = 0.237 \pm 0.015$. This concordance value is indistinguishable from the WMAP3 cosmology but is not consistent with that of Planck: there is a tension in $\Omega_m$ as well as $H_0$. These tensions have emerged as progressively higher multipoles have been incorporated into CMB fits. This temporal evolution is suggestive of a systematic effect in the analysis of CMB data at fine angular scales, and may be related to the observation of unexpectedly massive galaxies at high redshift. These are overabundant relative to $\Lambda$CDM predictions by an order of magnitude at $z > 7$. Such massive objects are anomalous and could cause gravitational lensing of the surface of last scattering in excess of the standard calculation made in CMB fits, potentially skewing the best-fit cosmological parameters and contributing to the Hubble tension.