On the ages of the stellar populations of galaxies at $z=0.1$-7

TL;DR

This study analyzes galaxy ages across a wide redshift range using JWST and HST data, revealing that most galaxies' ages evolve with redshift, but some appear older than the Universe, possibly due to systematic errors.

Contribution

It provides new insights into galaxy age evolution at high redshifts without assuming cosmological parameters, highlighting potential systematic errors affecting age estimates.

Findings

Majority of galaxies show age evolution consistent with cosmology

Approximately 40% of galaxies appear older than the Universe

Systematic errors like degeneracies may explain anomalously old ages

Abstract

Recent studies have reported a non evolution of galaxy ages at redshifts higher than $z\sim$ 2.5, as well as galaxies older than the Universe. In this work, a sample of galaxies from JWST and HST was analysed via photometry to further understand this astronomical phenomenon. No prior cosmological parameters were assumed in the analysis, but the spectroscopic redshift. When compared to stellar population synthesis models, the results for mass-weighted galaxy ages indicate that the analysed objects seem to be divided into two subsets. The results for the subset with the majority of objects (60\% assuming a flat-$\Lambda$CDM cosmology) indicate an evolution of galaxy ages within the redshift range $z$=0.1-7.0, in the sense that higher redshift galaxies are younger than the Universe. Sources of systematic errors were discussed drawing into conclusion that degeneracies between reddening-age-metallicity, and/or AGN emission may explain the rest 40\% of the galaxies with ages older than expected from a flat-$\Lambda$CDM cosmology.