Constructing lightcones from cosmological N-body simulations

Future large scale galaxy surveys will map the distribution of matter in our universe at unprecedented distances and resolution. We cannot measure cosmological parameters directly from this survey data but rather, we need to compare these observations with data generated by N-body simulations created with known cosmological parameters. In order to make this comparison, we need to construct a representation of the matter past light cone that can be directly compared with the survey data. This study examines the various techniques that can be used to construct such lightcones from the output of N-body simulations, and seeks to evaluate their relative accuracies. We have analysed the impact of lightcone construction methodology on the weak lensing shear angular power spectrum by employing a lensing simulation algorithm. We find that lightcones generated using a snapshot interpolation methodology suffer from anomalous power spectrum peaks on sub-halo scales, which are likely to have a significant impact on their use in validating the results from upcoming galaxy-galaxy lensing surveys.