Local analogues of reionization-era galaxies seen with MUSE

Understanding how reionization occurred remains a milestone, and it is one of the main scientific drivers of current and future observational facilities. Detecting nebular HeII1640,4686 AA emission implies the presence of a very hard UV spectrum (E ≥ 54 eV), and this 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 HeII ionization, its origin has remained intensely debated and challenging to explain, especially in metal-deficient star-forming galaxies. We discuss this 'HeII ionization problem' with special emphasis on the case of the region of HeII emission we revealed with MUSE in the galaxy SBS0335-052E, one the most extreme metal-poor galaxies known nearby. For other 24 extreme emission line galaxies, all Green Peas (GP) observed with MUSE, we present their physical and chemical properties. Out of these 24 GPs three show a nebular HeII line, including one confirmed LyC leaker. MUSE observations have provided unique information on these objects representing our local laboratories of the physical processes expected to operate in the EoR.