Abstract
Stellar Populations Helium has a high ionization potential of 24.6 electron volts. Galaxies that have emission lines of He ii in their spectra must contain sufficiently hot sources, such as extremely massive stars, to ionize interstellar helium. Perez-Montero et al. modeled multiple emission lines in the spectra of a sample of galaxies that each show He ii emission. They found that the effective temperatures of the radiation fields were higher than can be explained by conventional stellar population models. The authors argue that populations of Wolf-Rayet stars with low abundances of elements heavier than helium, surrounded by clumpy gas, can explain the observations. Astron. Astrophys. 643 , A80 (2020).
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