Outshining by Recent Star Formation Prevents the Accurate Measurement of High-z Galaxy Stellar Masses

TL;DR

This study reveals that recent star formation in high-redshift galaxies obscures older stellar populations, leading to significant uncertainties in stellar mass estimates derived from spectral energy distribution fitting.

Contribution

It demonstrates how ongoing star formation outshines earlier episodes, causing order of magnitude uncertainties in stellar mass measurements for early galaxies, based on cosmological simulations and SED fitting.

Findings

Order of magnitude uncertainties in stellar mass estimates for z>7 galaxies.

Recent star formation outshines older stellar populations, complicating mass inference.

Simulation-based evidence highlights the need for improved modeling techniques.

Abstract

In this paper, we demonstrate that the inference of galaxy stellar masses via spectral energy distribution (SED) fitting techniques for galaxies formed in the first billion years after the Big Bang carries fundamental uncertainties owing to the loss of star formation history (SFH) information from the very first episodes of star formation in the integrated spectra of galaxies. While this early star formation can contribute substantially to the total stellar mass of high-redshift systems, ongoing star formation at the time of detection outshines the residual light from earlier bursts, hampering the determination of accurate stellar masses. As a result, order of magnitude uncertainties in stellar masses can be expected. We demonstrate this potential problem via direct numerical simulation of galaxy formation in a cosmological context. In detail, we carry out two cosmological simulations with significantly different stellar feedback models which span a significant range in star formation history burstiness. We compute the mock SEDs for these model galaxies at z=7 via 3D dust radiative transfer calculations, and then backwards fit these SEDs with Prospector SED fitting software. The uncertainties in derived stellar masses that we find for z>7 galaxies motivate the development of new techniques and/or star formation history priors to model early Universe star formation.