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Annual Review of Astronomy and Astrophysics - Early Publication
Reviews in Advance appear online ahead of the full published volume. View expected publication dates for upcoming volumes.
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Ionizing Radiation Escape from Low-Redshift Galaxies and Its Connection to Cosmic Reionization
First published online: 04 April 2025More LessThe 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.
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Star Formation from Low to High Mass: A Comparative View
H. Beuther, R. Kuiper, and M. TafallaFirst published online: 01 April 2025More LessStar formation has often been studied by separating the low- and high-mass regimes with an approximate boundary at 8 M⊙. Although some of the outcomes of the star-formation process are different between the two regimes, it is less clear whether the physical processes leading to these outcomes are that different at all. Here, we systematically compare low- and high-mass star formation by reviewing the most important processes and quantities from an observational and theoretical point of view. We identify three regimes in which processes are either similar, quantitatively, or qualitatively different between low- and high-mass star formation.
- ▪ Similar characteristics can be identified for the turbulent gas properties and density structures of the star-forming regions. Many of the observational characteristics also do not depend that strongly on the environment.
- ▪ Quantitative differences can be found for outflow, infall, and accretion rates as well as mean column and volume densities. Also, the multiplicity significantly rises from low- to high-mass stars. The importance of the magnetic field for the formation processes appears still less well constrained.
- ▪ Qualitative differences between low- and high-mass star formation relate mainly to the radiative and ionizing feedback that occurs almost exclusively in regions forming high-mass stars. Nevertheless, accretion apparently can continue via disk structures in ionized accretion flows.
Finally, we discuss to what extent a unified picture of star formation over all masses is possible and which issues need to be addressed in the future.
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