Affiliation: University of Geneva

Contribution: Oral

Title: The UV-brightest starbursts in the distant Universe: extreme modes of galaxy formation and Lyman continuum escape

Abstract: UV-bright star-forming galaxies were believed to be extremely rare at any redshift, even at the epoch of reionization. However, James Webb Space Telescope (JWST) observations are dramatically changing this picture by revealing numerous UV-bright sources even at z~14, with volume densities exceeding model predictions for galaxy formation by an order of magnitude. Recent theoretical frameworks have provided different interpretations for these sources, including the need for very high star-formation efficiencies, initial mass function (IMF) variations, efficient radiation-driven outflows, or stochastic variability of the star formation. The nature of these monsters remains enigmatic and unknown, however, it may completely change our understanding of the early formation of massive galaxies and cosmic reionization.

In this talk, I will present recent HST, VLT, and ALMA observations of a new class of extremely UV-bright star-forming galaxies discovered at intermediate redshifts (z~2-4). These sources are characterized by very young stellar populations with Very Massive Stars (M > 100 Msun), Lyman continuum (LyC) leakage up to fesc(LyC)~90%, and extremely high star formation efficiencies (>40%), possibly representing early stages of strong and UV-bright starbursts at high redshift like the ones recently uncovered with JWST at z > 7. Furthermore, these newly discovered sources show high star formation rates (SFR ~ 500-1000 Msun/yr) within extremely compact sizes (~200-500 pc), a process that strongly resembles traditional models of monolithic collapse, in which a very large mass of stars (1e9 – 1e10 Msun) formed within a remarkably short time (<10 Myr). I will highlight some unique properties observed in these sources, including complex Lyman-alpha profiles, high S/N Lyman continuum emission, unique stellar populations, and SEDs. Finally, I will discuss the possible implications of these UV-bright sources in the broader context of galaxy formation and cosmic reionization.

This contribution can be found here (pdf).