The origin of strong nebular HeII emission at low and high redshift

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Recent observations of high redshift show very high ionized nebular lines Similar lines are extremely rare in low redshift galaxies and there mostly connected to hot, evolved Wolf-Rayet stars. Now it appears that a very small number of localgalaxies exist, which show such highly ionized nebular lines without signatures of Wolf-Rayet stars. We propose to study these potential local analogs to the highly ionized young galaxies in order to better understand the ionization mechanisms of these lines. This will allow to clarify, if the observed high-ionization lines in some high redshift starbursts (proto-)galaxies are indeed created by the radiation field of extremely metal-poor, very massive stars.