SIMULATION OF ASTRONOMICAL IMAGES FROM OPTICAL SURVEY TELESCOPES USING A COMPREHENSIVE PHOTON MONTE CARLO APPROACH

Abstract

We present a comprehensive methodology for the simulation of astronomical\nimages from optical survey telescopes. We use a photon Monte Carlo approach to\nconstruct images by sampling photons from models of astronomical source\npopulations, and then simulating those photons through the system as they\ninteract with the atmosphere, telescope, and camera. We demonstrate that all\nphysical effects for optical light that determine the shapes, locations, and\nbrightnesses of individual stars and galaxies can be accurately represented in\nthis formalism. By using large scale grid computing, modern processors, and an\nefficient implementation that can produce 400,000 photons/second, we\ndemonstrate that even very large optical surveys can be now be simulated. We\ndemonstrate that we are able to: 1) construct kilometer scale phase screens\nnecessary for wide-field telescopes, 2) reproduce atmospheric\npoint-spread-function moments using a fast novel hybrid geometric/Fourier\ntechnique for non-diffraction limited telescopes, 3) accurately reproduce the\nexpected spot diagrams for complex aspheric optical designs, and 4) recover\nsystem effective area predicted from analytic photometry integrals. This new\ncode, the photon simulator (PhoSim), is publicly available. We have implemented\nthe Large Synoptic Survey Telescope (LSST) design, and it can be extended to\nother telescopes. We expect that because of the comprehensive physics\nimplemented in PhoSim, it will be used by the community to plan future\nobservations, interpret detailed existing observations, and quantify\nsystematics related to various astronomical measurements. Future development\nand validation by comparisons with real data will continue to improve the\nfidelity and usability of the code.\n