High-resolution imaging of the ionizing and non-ionizing radiation of extreme starbursts at z 2.4

We used to think that cosmic reionization was likely dominated by faint, widely-distributed galaxies until recent results have shown that UV-bright galaxies i) are among the most powerful ionizing sources known, and ii) they appear to be much more numerous than previously thought at the Epoch of Reionization (EoR). These results are enigmatic, however, may completely change our understanding of the nature of very UV-bright galaxies and the potential role these sources play in cosmic reionization. This proposal aims to probe the nature of extremely UV-bright galaxies and the mode of escape of ionizing photons.

Here we request high-resolution HST imaging of a representative sample of nine very UV-bright star-forming galaxies at z=2.3-2.5, possibly analogs of EoR bright sources recently uncovered with JWST and HST. These are extremely young (<10Myr), powerful, and very efficient starbursts, showing already hint at very high Lyman continuum (LyC) escape from available high-resolution and high S/N continuum spectra covering Ly-alpha to H-alpha. WFC3/UVIS imaging will probe the ionizing (~750A) and non-ionizing (~1600A) radiation at similar spatial scales (down to ~500pc) to test the LyC escape in these exceptional sources, including very efficient modes of production and escape of ionizing photons, and provide the first high-resolution studies of their morphologies. The requested observations will thus uncover some of the most important, but still open questions raised by these UV-bright sources, including those related to their origin and nature, and their potential role in cosmic reionization.