Astronomy and Astrophysics – Astrophysics
Scientific paper
1998-12-11
Astronomy and Astrophysics
Astrophysics
5 pages, 3 figures, to appear in the proceedings of "After the Dark Ages: When Galaxies were Young (the Universe at 2<z<5)", 9
Scientific paper
10.1063/1.58611
Observations of resolved HeII Lyman alpha absorption in spectra of two QSO's suggest that the epoch of helium ionization occurred at z~3. Proximity zones in the spectra of the quasars (z=3.18, 3.285) at 304 A resemble Stromgren spheres, suggesting that the intergalactic medium is only singly ionized in helium. We present models of the proximity effect which include the full physics of the ionization, heating and cooling and an accurately simulated inhomogeneous gas distribution. In these models the underdense intergalactic medium is heated to at least 10,000-20,000 K after cooling to as low as a few 1000 K due to cosmological expansion, with higher temperatures achieved farther away from the quasar due to absorption-hardened ionizing spectra. The quasars turn on for a few times 10^7 years with a fairly steady flux output at 228 A comparable to the 304 A flux output directly observed with HST. The recoveries in the spectra occur naturally due to voids in the IGM and may provide a fairly model-independent probe of the baryon density.
Anderson Scott F.
Hogan Craig J.
Wadsley James W.
No associations
LandOfFree
The Full Re-Ionization of Helium does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Full Re-Ionization of Helium, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Full Re-Ionization of Helium will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-166412