Speaker
Dr
Luca Graziani
(Max Planck Institute for Astrophysics - MPA Garching)
Description
The helium reionisation and the cosmic UV background (UVB) at z=3 have been investigated in recent years both theoretically and observationally. Spatial fluctuations of the eta parameter in the Lyα forest show that the He II opacity is “patchy” and a theoretical modelling of the UVB spectral shape is necessary to constrain these fluctuations. Metal ions in the IGM help constraining the UVB spectral shape at the edge of HeI and HeII ionisation potentials. I will show the results of a new radiative transfer (RT) simulation performed with the code CRASH3, accounting for metal ionisation states self consistently with H and He. The importance of the RT effects in shaping the UV background on a scale of 10/h Mpc comoving, is discussed by providing an accurate estimate of the fluctuations in eta, in the IGM temperature and in the column density ratio CIV/SiIV.
