Understand
In a recent study star-forming galaxies with HeII emission between redshifts 2 and 4.6 have been found to occur in two modes, distinguished by the width of their HeII emission lines.
- Broad HeII emission has been attributed to stellar emission from a population of evolved Wolf-Rayet (WR) stars while narrow HeII emission has been attributed to nebular emission excited by a population of very hot PopIII stars formed in pockets of pristine gas at moderate redshifts.
- In this work we propose an alternative scenario for the origin of the narrow HeII emission, namely very massive stars (VMS) at low metallicity (Z) which form strong but slow WR-type stellar winds due to their proximity to the Eddington limit.
- We estimate the expected HeII line fluxes and equivalent widths based on wind models for VMS and population synthesis models, and compare the results with recent observations of star-forming galaxies at moderate redshifts.