Computer Science
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...7e..17m&link_type=abstract
The Universe at z > 6, 26th meeting of the IAU, Joint Discussion 7, 17-18 August 2006, Prague, Czech Republic, JD07, #17
Computer Science
Scientific paper
We discuss the robustness of constraints on the intergalactic medium neutral hydrogen fraction inferred from the extent of HII regions of high redshift quasars by means of their absorption spectra. We have combined state-of-art SPH and 3D Radiative Transfer (RT) simulations to extract a sample of mock quasar spectra and we have analyzed such a sample with a procedure commonly adopted in real observations. Our analysis shows that the size of the quasar HII regions measured in quasar spectra strongly underestimate the real HII extent, as a result of absorption by residual neutral hydrogen inside the HII region and red damping wing absorption produced by HI just outside the HII region. We demonstrate that, even an idealized large sample of observed spectra -with negligible uncertainties on the quasars parameters (ie. lifetime, luminosity)- is compatible with a surrounding IGM whose mean IGM neutral hydrogen fraction can range freely in the interval [0.05,1] . We conclude, that our current knowledge of the re-ionization process is not accurate enough to allow a direct conversion of the quasars HII region extent into a value for the mean IGM ionization fraction. Finally, we propose a statistical method which could allow to extract such information from a large sample of quasar spectra at z>6.
Choudury T. S.
Ferrara Andrea
Gallerani Simona
Maselli Alessandro
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