An investigation of the origin of He II nebular emission in spectra of low-metallicity H II regions from Sloan Digital Sky Survey

1Agiienko, KB
1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
Kinemat. fiz. nebesnyh tel (Online) 2013, 29(5):25-35
Start Page: Extragalactic Astronomy
Language: Russian

We study possible sources of hard ionising radiation in H II regions with low metallicity. The presence of the nebular He II λ 468.6 nm emission line in the H II region spectrum can be considered as an indication of this radiation. While theoretical stellar population synthesis models predict He II emission-line intensities decreasing with the metallicity, the intensity of this line in H II regions from our sample is increasing with metallicity decrease. That is in good agreement with previous studies. Some relation between the He II emission and presence of Wolf — Rayet (WR) stars is discussed. Only 30 % of spectra from our sample show nebular emission superposed with broad He II emission from WR stars. This evidence does not exclude WR stars as a possible source of hard ionising radiation in some H II regions. However, other sources such as fast radiative shocks seem to be more likely.

Keywords: Nebular He II, SLOAN

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