SAMPLE VARIANCE IN N-BODY SIMULATIONS AND IMPACT ON TOMOGRAPHIC SHEAR PREDICTIONS.

We study the effects of sample variance in N-body simulations as a function of the size of the simulation box, namely in connection with predictions on tomographic shear spectra. We make use of a set of eight ΛCDM simulations in boxes of 128, 256, and 512 a side, for a total of 24, differing just by the initial seeds. Among the simulations with 128 and 512 a side, we suitably select those closest and farthest from average. Numerical and linear spectra are suitably connected at low k to evaluate the effects of sample variance on shear spectra for 5 or 10 tomographic bands. We find that shear spectra obtained by using 128 simulations can vary up to , just because of the seed. The sample variance lowers to when using 512 Mpc. These percentages could however slightly vary if other sets of the same number of realizations were considered. Accordingly, in order to match the precision expected for the data, if still using eight boxes, we require a size of – for them. [ABSTRACT FROM AUTHOR]