Star formation and AGN activity 500 Myr after the Big Bang: Insights from JWST

TL;DR

This study shows that including AGN components in spectral energy distribution fitting of high-redshift galaxies significantly reduces estimated star formation rates and stellar masses, impacting our understanding of early galaxy evolution.

Contribution

It introduces the importance of accounting for AGN activity in SED fitting of early galaxies, revealing lower star formation rates and masses than previously estimated.

Findings

Cosmic star formation history is ~0.4 dex lower at z>9.5 with AGN inclusion.

Individual stellar masses and SFRs can be up to 4 dex lower when AGN are considered.

Including AGN components resolves excess star formation issues at high redshift.

Abstract

We consider the effect of including an active galactic nuclei (AGN) component when fitting spectral energy distributions of 109 spectroscopically confirmed $z\approx 3.5-12.5$ galaxies with JWST. Remarkably, we find that the resulting cosmic star formation history is $\approx 0.4$ dex lower at $z\gtrsim 9.5$ when an AGN component is included in the fitting. This alleviates previously reported excess star formation at $z\gtrsim 9.5$ compared to models based on typical baryon conversion efficiencies inside dark matter halos. We find that the individual stellar masses and star formation rates can be as much as $\approx 4$ dex lower when fitting with an AGN component. These results highlight the importance of considering both stellar mass assembly and supermassive black hole growth when interpreting the light distributions of among the first galaxies to ever exist.