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16 juin 2017 Tout le mois

Carolina Kehrig (IAA-CSIC, Granada) — Nebular HeII emission from spatially resolved metal-poor star-forming galaxies

Vendredi 16 juin 2017 11:00-12:00 - Amphi

Abstract : Nebular HeII emission (at 1640 A and 4686 A in the rest-frame UV and optical ranges, respectively), observed to be more frequent in high-z galaxies than locally, is indicative of far harder ionizing spectrum than that seen in nearby systems. Star-forming galaxies with lower metal content tend to have a larger narrow (nebular) HeII intensities compared to those with higher metallicities. This agrees with the expected harder spectral energy distribution at the lower metallicities typical in the early universe. Theoretical arguments suggest that Population III stars have spectra hard enough to produce many HeII-ionizing photons. So the high-ionization HeII line has been considered one of the best signatures to single out candidates for PopIII-host galaxies and it is also a useful window into the ionizing spectrum of metal-poor hot stars. But, despite various attempts to explain the formation of nebular HeII emission, its origin remains mysterious in many cases both at high and low redshifts. Before interpreting high-z HeII emitters, it is crucial to understand HeII ionization nearby. I will discuss possible HeII-ionizing sources and what we can learn studying local, metal poor HeII-emitting galaxies by spatially resolving them.

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