3D-IMS: Accurately Modeling the Lyman-alpha Forest in Collisionless Simulations
Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, I present “3D Iteratively Matched Statistics” (3D-IMS), a novel method to accurately model the Lyman-alpha forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. I compare the results given by 3D-IMS with a reference high-resolution hydrodynamic simulation, demonstrating that 3D-IMS can reproduce the probability density function (PDF), line-of-sight and 3D power spectra of the Lyman-alpha forest with high accuracy. I also show that commonly used approximate methods to model such statistics from N-body simulations are not suitable when large volumes (>~100 cMpc) are needed. The 3D-IMS method could be used to improve our understanding about the 3D correlations of the Lyman-alpha flux measured from BOSS, and their relation with the thermal state of the IGM or other small scale physics. This could increase the accuracy of the estimate of the BAO scale.