Investigation of the origin of nebular HeII emission in the spectra of low-metallicity HII regions from the Sloan Digital Sky Survey

Abstract

Primordial stars apparently were very hot and massive and emitted a lot of hard ionizing radiation.Regions of ionized hydrogen are the best places for studying such hard radiation, because of underlying starformation processes. To check a possible links between hard ultraviolet radiation and Wolf–Rayet (WR) stars we created a sample of galaxies with nebular emission line of HeII λ4686 from Sloan Digital Sky Service. Theoretical models predict decreasing of HeII emission line intensity with metallicity. Data from our sample did not show any significant trends. This observation is in good agreement with previous studies. Only a half of spectra from our sample show nebular HeII emission, superposed on broad HeII emission from WR stars. This point concludes that not only WR stars are responsible for origin of nebular HeII emission, but also other mechanisms make a contribution into hard ionizing radiation at HII regions.

Keywords

• active processes and star formation in galaxies
• intensity of emission lines
• Wolf–Rayet stars