Simulating intergalactic quasar scintillation
  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 $\nu_{s}\gsim30$
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 \textit{Planck}.
