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Approaching the mystery of HeII with MUSE (2nd May 2019 Colloquium by Themiya Nanayakkara)

Submitter: Themiya Nanayakkara (Leiden University)
Description: In the quest to study early star-formation physics in the universe, one of the most sought after tracers is HeIIλ1640, with its presence in the lack of other metal emission/absorption lines generally being interpreted as evidence for metal-poor stellar populations. HeIIλ1640 ionizing photons are produced via sources of hard ionizing radiation and requires photons with energies >=54.4eV.
Though many ionizing sources have been suggested, stellar population models are still unable to accurately predict the HeIIλ1640 features while being consistent with other observed emission line diagnostics.
The development of sensitive multiplex instruments such as MUSE in the VLT has allowed us to obtain deep rest-UV spectroscopy of galaxies at z~2-4 to build up samples of HeIIλ1640 emitters at cosmic noon, where galaxies are rapidly forming stars and evolving to build up most of the observed baryonic mass in the Universe. In our quest to understand the ISM of galaxies at z=2-4 via rest-UV emission lines, we have obtained the largest sample of HeIIλ1640 emitters at high-redshift. By using the deep state-of-the-art data from several MUSE GTO surveys, I will present results from the first study of the ISM of individual HeIIλ1640 emitters at these redshifts.
I will discuss the role of dust and binaries in stellar populations and photo-ionisation modelling and link to how we can use observed correlations between observed and modelled spectra to understand mechanisms of HeII production in the early universe. I will also provide and outlook for what we expect in the era of future extra deep MUSE GTO surveys and JWST.
Copyright: ESO
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