Adding Value to JWST Spectra and Photometry: Stellar Population and Star Formation Properties of Spectroscopically Confirmed JADES and CEERS Galaxies at $z > 7$

TL;DR

This study analyzes high-redshift galaxies at z > 7 using JWST data, revealing rising star formation rates, differences between spectroscopic and photometric measurements, and insights into galaxy morphology and starburst activity.

Contribution

It provides a comprehensive comparison of spectroscopic and photometric properties of z > 7 galaxies, highlighting the rising star formation history and the distribution of ionized gas emission.

Findings

SFRs from Hβ are 2-13 times higher than UV-based estimates.

Photometric EW measurements are on average 30% smaller than spectroscopic ones.

Line-emitting galaxies show similar morphology to continuum emission.

Abstract

In this paper, we discuss measurements of the stellar population and star forming properties for 43 spectroscopically confirmed publicly available high-redshift $z > 7$ JWST galaxies in the JADES and CEERS observational programs. We carry out a thorough study investigating the relationship between spectroscopic features and photometrically derived ones, including from spectral energy distribution (SED) fitting of models, as well as morphological and structural properties. We find that the star formation rates (SFRs) measured from H$\beta$ line emission are higher than those estimated from Bayesian SED fitting and UV luminosity, with ratios SFR$_{H\beta}$/ SFR$_{UV}$ ranging from 2~13. This is a sign that the star formation history is consistently rising given the timescales of H$\beta$ vs UV star formation probes. In addition, we investigate how well equivalent widths (EWs) of H$\beta$ $\lambda$4861, [O III] $\lambda$4959, and [O III] $\lambda$5007 can be measured from photometry, finding that on average the EW derived from photometric excesses in filters is 30% smaller than the direct spectroscopic measurement. We also discover that a stack of the line emitting galaxies shows a distinct morphology after subtracting imaging that contains only the continuum. This gives us a first view of the line or ionized gas emission from $z > 7$ galaxies, demonstrating that this material has a similar distribution, statistically, as the continuum. We also compare the derived SFRs and stellar masses for both parametric and non-parametric star formation histories, where we find that 35% of our sample formed at least 30% of their stellar mass in recent (< 10 Myr) starburst events.