Simulating intergalactic quasar scintillation

Intergalactic scintillation of distant quasars is sensitive to free electrons and there-fore complements Lyα absorption line experiments probing the neutral intergalactic medium (IGM). We present a new scheme to compute IGM refractive scintillation ef-fects on distant sources in combination with Adaptive Mesh Refinement cosmological simulations. First we validate our model by reproducing the well-known interstel-lar scintillation (ISS) of Galactic sources. The simulated cosmic density field is then used to infer the statistical properties of intergalactic scintillation. Contrary to pre-vious claims, we find that the scattering measure of the simulated IGM at z 2 is 〈SMequ 〉 = 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 (νs = 5 GHz) up to 0.2 (νs = 50 GHz); above νs ∼ 30 GHz the IGM contribution dominates over ISS modulation. We compare our model with data from a 0.3 6 z 6 2 quasar sample observed at νobs = 8.4 GHz. For this high frequency (10.92 6 νs 6 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 con-clude 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. Key words: cosmology: simulation – intergalactic medium – interstellar medium – scintillation. 1