He II and H I Absorption studies with FUSE and VLT

Details He II and H I Absorption studies with FUSE and VLT He II and H I Absorption studies with FUSE and VLT

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...199.1805s&link_type=abstract

American Astronomical Society, 199th AAS Meeting, #18.05; Bulletin of the American Astronomical Society, Vol. 33, p.1337

Astronomy and Astrophysics

Astronomy

Scientific paper

We provide an in-depth analysis of the He II and H I absorption in the intergalactic medium at z = 2.3-2.9 toward HE 2347-4342, using FUSE, Keck, and VLT spectra. Following up on the study of Kriss et al. (2001, Science, 293, 1112), our analysis focuses on the small-scale variability in the He II/H I ratios with redshift, which probably reflects the nature of the ionizing sources. We use photoionization models to understand the ionizing background and its possible changes at z < 2.7 arising from the overlap of helium ionization fronts from early sources. The He II Lyα absorption is visible as small-scale fluctuations in absorption between 2.3 <= z <= 2.7. We compare the Keck and VLT data, including a Lyman Limit system at za = 2.75 (3420 Å). Many of the He II features have H I counterparts with log N(H I) > 12.2, accounting for much of the observed He II opacity. The ratio η = N(He II)/N(H I) ranges from 1 to >1000. Ratios of η < 100 are consistent with photoionization of the absorbing gas by a hard ionizing spectrum resulting from the quasar background, but ratios η > 100 in many locations indicate additional contributions from starburst galaxies or heavily filtered quasar radiation. The ionizing spectra may help to explain the difference between the reionization epochs of He II (z ≈ 2.8 +/- 0.2) and H I (z ≈ 6.2 +/- 0.2)

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