Carolina Kehrig
Instituto de Astrofísica de Andalucia, Granada, Spain

Abstract
Understanding how the Universe was reionized remains a milestone, and it is one of the main scientific drivers of current and future observational facilities (e.g. VLT/MUSE, JWST, ELT). Detecting high-ionizing emission features, as the nebular HeII1640,4686 AA line,  implies the presence of a very hard UV spectrum (E ≥ 54 eV). In particular, such line is believed to be a potential tracer of PopIII and nearly metal-free stars, and  their hosts. Despite the  great deal of effort dedicated to understanding the high-ionisation phenomenon, its origin has remained intensely debated and challenging to explain, especially in metal-deficient star-forming galaxies near and far. We discuss this ‘HeII ionization problem’ in the context of the galaxies IZw18 and SBS0335-052E — the lowest metallicity HeII emitters known nearby which are rare and unique local analogues of the physical processes expected to operate in the Epoch of Reionization. We also present recent results on HeII emitters at cosmic noon and beyond, and progress in the field.

2026 June 22, 13:30

IA/U.Porto
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto