Intergalactic scintillation of distant quasars is sensitive to free electrons and therefore complements Ly \alpha absorption line experiments probing the neutral intergalactic medium ( IGM ) .
We present a new scheme to compute IGM refractive scintillation effects on distant sources in combination with Adaptive Mesh Refinement cosmological simulations .
First we validate our model by reproducing the well-known interstellar scintillation ( ISS ) of Galactic sources .
The simulated cosmic density field is then used to infer the statistical properties of intergalactic scintillation .
Contrary to previous claims , we find that the scattering measure of the simulated IGM at z < 2 is \langle \mbox { SM } _ { { equ } } \rangle = 3.879 , i.e .
almost 40 times larger than for the usually assumed smooth IGM .
This yield an average modulation index ranging from 0.01 ( \nu _ { s } = 5 GHz ) up to 0.2 ( \nu _ { s } = 50 GHz ) ; above \nu _ { s } \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 30 GHz the IGM contribution dominates over ISS modulation .
We compare our model with data from a 0.3 \leq z \leq 2 quasar sample observed at \nu _ { { obs } } = 8.4 GHz .
For this high frequency ( 10.92 \leq \nu _ { s } \leq 25.2 ) , high galactic latitude sample ISS is negligible , and IGM scintillation can reproduce the observed modulation with a 4 \% accuracy , without invoking intrinsic source variability .
We conclude by discussing the possibility of using IGM scintillation as a tool to pinpoint the presence of intervening high- z groups/clusters along the line of sight , thus making it a probe suitably complementing Sunyaev-Zeldovich data recently obtained by Planck .