UV Luminosity Functions from HST and JWST: A Possible Resolution to the High-Redshift Galaxy Abundance Puzzle and Implications for Cosmic Strings

TL;DR

This paper demonstrates that cosmic strings could explain the high abundance of early galaxies observed by JWST and HST without altering star formation models, and sets new constraints on cosmic string properties using UV luminosity functions.

Contribution

The study integrates cosmic strings into galaxy formation models to explain high-redshift galaxy counts and derives new upper bounds on cosmic string tension from UV luminosity functions.

Findings

Cosmic strings can account for the observed galaxy abundance at high redshifts.

New upper bound on cosmic string tension: Gμ ≲ 10^{-8}.

UV luminosity functions are a promising tool for constraining cosmic-string physics.

Abstract

Recent observations of high redshift galaxies by the James Webb Space Telescope suggest the presence of a bright population of galaxies that is more abundant than predicted by most galaxy formation models. These observations have led to a rethinking of these models, and numerous astrophysical and cosmological solutions have been proposed, including cosmic strings, topological defects that may be remnants of a specific phase transition in the very early moments of the Universe. In this paper, we integrate cosmic strings, a source of nonlinear and non-Gaussian perturbations, into the semi analytical code Zeus21, allowing us to efficiently predict the ultraviolet luminosity function (UVLF). We conduct a precise study of parameter degeneracies between star-formation astrophysics and cosmic-string phenomenology. Our results suggest that cosmic strings can boost the early-galaxy abundance enough to explain the measured UVLFs from the James Webb and Hubble Space Telescopes from redshift z = 4 to z = 17 without modifying the star-formation physics. In addition, we set a new upper bound on the string tension of $G\mu \lessapprox 10^{-8}$ ($95\%$ credibility), improving upon previous limits from the cosmic microwave background. Although with current data there is some level of model and prior dependence to this limit, it suggests that UVLFs are a promising avenue for future observational constraints on cosmic-string physics.