RELICS: Small Lensed $z\geq5.5$ Galaxies Selected as Potential Lyman Continuum Leakers

TL;DR

This study measures sizes of 78 high-redshift galaxies, identifying small, compact, star-forming galaxies that could be significant contributors to cosmic reionisation, using gravitational lensing and advanced modeling.

Contribution

It provides detailed size measurements of high-redshift galaxies and identifies potential Lyman continuum leakers, advancing understanding of early galaxy properties and reionisation sources.

Findings

Many small galaxies with radii <200 pc confirmed at high redshift

Identification of compact, highly star-forming galaxies as potential reionisation contributors

Size-magnitude relation consistent with previous studies

Abstract

We present size measurements of 78 high-redshift ($z\geq 5.5$) galaxy candidates from the Reionisation Lensing Cluster Survey (RELICS). These distant galaxies are well-resolved due to the gravitational lensing power of foreground galaxy clusters, imaged by the Hubble Space Telescope (HST) and the Spitzer Space Telescope. We compute sizes using the forward-modeling code Lenstruction and account for magnification using public lens models. The resulting size-magnitude measurements confirm the existence of many small galaxies with effective radii $R_{\rm{eff}}<200$ pc in the early universe, in agreement with previous studies. In addition, we highlight compact and highly star-forming sources with star formation rate surface densities $\Sigma_\text{SFR}>10M_\odot\text{yr}^{-1}\text{kpc}^{-2}$ as possible Lyman continuum leaking candidates that could be major contributors to the process of reionisation. Future spectroscopic follow-up of these compact galaxies (e.g., with the James Webb Space Telescope) will further clarify their role in reionisation and the physics of early star formation.