High-z nebulae: Ionization by stars or by an obscured QSO?

Details High-z nebulae: Ionization by stars or by an obscured QSO? High-z nebulae: Ionization by stars or by an obscured QSO?

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003a%26a...405..975b&link_type=abstract

Astronomy and Astrophysics, v.405, p.975-980 (2003)

Astronomy and Astrophysics

Astrophysics

10

Line: Formation, Quasars: Emission Lines, Galaxies: Formation, Cosmology: Early Universe

Scientific paper

The gravitational arc observed by Holden et al. at z=3.356 reveals strong emission lines of N IV] lambda 1485, C IV lambda lambda 1549, O III]lambda 1665 but no N V lambda 1240. The lines were modelled assuming photoionization by a thermal distribution hotter than 60 000 K. This paper considers an alternative ionizing source consisting of a partially absorbed powerlaw. We compare the line ratios from a low metallicity nebula (Ztotal = 0.05 Zsun) photoionized by such filtered continuum with those produced by a zero-metallicity star of Teff= 80 000 K. We find that the latter generally produces stronger emission lines of C, N and O than the absorbed powerlaw, even when their respective He II/Hβ ratio is matched. The absorbed powerlaw generates N V lambda 1240, O VI lambda 1035 and [Ne V] lambda 1240 nebular lines weaker than the canonical direct powerlaw, although at a much higher level than the 80 000 K stellar atmosphere. As a result of the large partially ionized zone created by the absorbed powerlaw, the optical [O I] lambda 6300 and [S II]lambda 6731 lines and the C II] lambda 2326 and Mg II lambda lambda 2800 lines in the UV are much stronger than in the stellar case. These constitute the best discriminant for differentiating the predictions of the absorbed case from those of the stellar model.

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