Bridging Theory and Observations: Insights into Star Formation Efficiency and Dust Attenuation in $z > 5$ Galaxies

TL;DR

This study models early galaxy evolution at high redshift, successfully reproducing observed properties and revealing the regulation of star formation efficiency by gas flows, while highlighting the significant impact of dust attenuation on observed luminosities.

Contribution

It introduces a self-consistent, radially-resolved model that matches JWST observations and explores the regulation of star formation efficiency and dust effects in early galaxies.

Findings

Star formation efficiency is regulated by gas inflows and outflows.

Predicted dust attenuation can obscure UV luminosities significantly.

Discrepancies suggest mechanisms like dust evacuation are needed.

Abstract

We investigate early galaxy evolution by modeling self-consistently their radially-resolved evolution of gas, stars, heavy elements, and dust content. Our model successfully reproduces various observed properties of JWST-identified galaxies at $z > 5$, including sizes, stellar masses, star formation rates (SFR), metallicities, and dust-to-stellar mass ratios. We show that the star formation efficiency (SFE), $f_\ast \equiv {\rm SFR}/(f_{\rm b} \dot{M}_{\rm h})$, is regulated by the global equilibrium between cosmological gas inflows, star formation, and gas outflows. Our model predicts $f_\ast \lesssim 20~\%$ for galaxies with halo masses of $M_{\rm h} \sim 10^{11-12}\, M_\odot$ down to $z = 5$, allowing them to reach intrinsic UV magnitudes of $M_{\rm UV} \lesssim -22~{\rm mag}$; when dust attenuation is ignored, the predicted UV luminosity function (LF) at $z \sim 12$ agrees well with observations. However, our model also suggests that these galaxies would be heavily obscured by dust, with high optical depths at 1500~\AA~of $\tau_{1500} \gtrsim 10$, causing the dust-attenuated UV LF to fall significantly below the observed one. This discrepancy highlights the need for mechanisms that mitigate strong dust attenuation, such as dust evacuation from star-forming regions and/or preferential production of large dust grains. Further exploration of these processes is essential for understanding the early stages of galaxy evolution.