Inferred galaxy properties during Cosmic Dawn from early JWST photometry results

TL;DR

This study uses JWST photometry and cosmological simulations to infer properties of early galaxies during Cosmic Dawn, exploring contributions of black holes and stellar populations, and assessing the robustness of stellar mass estimates.

Contribution

It introduces a modeling approach combining JWST data with galaxy scaling relations to estimate high-redshift galaxy properties, including potential AGN activity.

Findings

Stellar masses are similar or slightly higher than previous estimates.

Most galaxy spectra are dominated by stellar emission.

Some high-redshift candidates may host active galactic nuclei.

Abstract

Early photometric results from JWST have revealed a number of galaxy candidates above redshift 10. The initial estimates of inferred stellar masses and the associated cosmic star formation rates are above most theoretical model predictions up to a factor of 20 in the most extreme cases, while this has been moderated after the recalibration of NIRCam and subsequent spectroscopic detections. Using these recent JWST observations, we use galaxy scaling relations from cosmological simulations to model the star formation history to very high redshifts, back to a starting halo mass of 10^7 solar masses, to infer the intrinsic properties of the JWST galaxies. Here we explore the contribution of supermassive black holes, stellar binaries, and an excess of massive stars to the overall luminosity of high-redshift galaxies. Despite the addition of alternative components to the spectral energy distribution, we find stellar masses equal to or slightly higher than previous stellar mass estimates. Most galaxy spectra are dominated by the stellar component, and the exact choice for the stellar population model does not appear to make a major difference. We find that four of the 12 high-redshift galaxy candidates are best fit with a non-negligible active galactic nuclei component, but the evidence from the continuum alone is insufficient to confirm their existence. Upcoming spectroscopic observations of z > 10 galaxies will confirm the presence and nature of high-energy sources in the early universe and will constrain their exact redshifts.