Do the Early Galaxies observed by JWST disagree with Planck's CMB polarization measurements?

TL;DR

Recent JWST observations of massive galaxies at high redshift challenge the standard $b extbackslash Lambda$CDM cosmology constrained by Planck's CMB data, suggesting potential tensions or the need for new physics.

Contribution

This paper confirms the discrepancy between JWST galaxy densities and Planck CMB measurements within the $3b extbackslash Lambda$CDM model, exploring implications for cosmology and potential resolutions.

Findings

JWST galaxies at $z\,\sim 10$ are denser than predicted by $3b extbackslash Lambda$CDM.

Standard $3b extbackslash Lambda$CDM is excluded at over 99.7% confidence level for typical star formation efficiency.

Ignoring Planck's large-scale polarization data can reconcile JWST observations with $3b extbackslash Lambda$CDM.

Abstract

The recent observations from the James Webb Space Telescope have led to a surprising discovery of a significant density of massive galaxies with masses of $M \ge 10^{10.5} M_{\odot}$ at redshifts of approximately $z\sim 10$. This corresponds to a stellar mass density of roughly $\rho_*\sim 10^6 M_{\odot} Mpc^{-3}$. Despite making conservative assumptions regarding galaxy formation, this finding may not be compatible with the standard $\Lambda$CDM cosmology that is favored by observations of CMB Anisotropies from the Planck satellite. In this paper, we confirm the substantial discrepancy with Planck's results within the $\Lambda$CDM framework. Assuming a value of $\epsilon=0.2$ for the efficiency of converting baryons into stars, we indeed find that the $\Lambda$CDM model is excluded at more than $99.7 \%$ confidence level (C.L.). An even more significant exclusion is found for $\epsilon \sim 0.1$, while a better agreement, but still in tension at more than $95 \%$, is obtained for $\epsilon =0.32$. This tension, as already discussed in the literature, could arise either from systematics in the JWST measurements or from new physics. Here, as a last-ditch effort, we point out that disregarding the large angular scale polarization obtained by Planck, which allows for significantly larger values of the matter clustering parameter $\sigma_8$, could lead to better agreement between Planck and JWST within the $\Lambda$CDM framework. Interestingly, the model compatible with Planck temperature-only data and JWST observation also favors a higher Hubble constant $H_0=69.0\pm1.1$ km/s/Mpc at $68\%$ C.L., in better agreement with observations based on SN-Ia luminosity distances.