2018/09/28 by Themiya Nanayakkara, Jarle Brinchmann, Nanayakkara, Themiya +3
Physics and Astronomy · #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #astro-ph.GA
paper · pdf · doi:10.48550/arxiv.1809.10970
To appear in Early Science with ELTs Proceedings IAU Symposium No. 347, 2018, 4 pages, 2 figures
arxiv created 2018/10/17 · arxiv updated 2018/10/18
HeII is the most sought-after emission line to detect and characterize metal free stellar populations. However, current stellar population/photo-ionization models lack sufficient He+ ionising photons to reproduce observed HeII fluxes while being consistent with other emission lines. Using ∼10-30 hour deep pointings from MUSE, we obtain ∼10 z∼2-4 HeIIλ1640 emitters to study their inter-stellar medium (ISM) and stellar population properties. Emission line ratio diagnostics of our sample suggest that emission lines are driven by star-formation in solar to moderately sub-solar (∼ 1/20th) metallicity conditions. However, we find that even after considering effects from binary stars, we are unable to reproduce the HeIIλ1640 equivalent widths (EWs). Our analysis suggest that extremely sub-solar metallicities (∼1/200th) are required to reproduce observed HeIIλ1640 luminosities. Thus, current stellar populations may require alternative mechanisms such as sub-dominant active galactic nuclei (AGN) or top heavy initial-mass-functions (IMFs) to compensate for the missing He+ ionising photons.