Ionizing Radiation Escape from Low-Redshift Galaxies and Its Connection to Cosmic Reionization

The escape of Lyman continuum (LyC) radiation from early galaxies transformed the intergalactic medium (IGM) and is intimately connected to the fueling and feedback processes that regulate galaxy evolution. IGM attenuation interferes with high-redshift LyC observations, but growing samples of LyC observations at z < 0.1 are revealing the properties of LyC-emitting galaxies. Along with multiwavelength observations of nearby LyC-emitting candidates, cosmological simulations, and simulations of LyC escape from star-forming clouds, recent studies are providing insights into the physics of LyC escape and the possible characteristics of the galaxies that reionized the Universe. Here, I review progress in LyC detections, the inferred indirect signatures of LyC escape and their application to high redshift, and our current understanding of the physical conditions that lead to high LyC escape. These findings include the following:

• ▪  LyC-emitting populations are diverse, and multiple factors correlate with LyC escape, particularly neutral gas absorption, dust attenuation, nebular ionization, and concentrated star formation.
• ▪  Radiative feedback plays a critical role in the youngest starbursts with the highest LyC escape fractions, but mechanical feedback may also contribute. Further research is needed to clarify the timing and role of different feedback mechanisms and to connect local LyC-production sites with the broader interstellar medium.

• ▪  Indirect LyC diagnostics show promise, but we need to understand whether and how the properties of LyC-emitting galaxies evolve from low to high redshift.