# PhoSim-NIRCam: Photon-by-photon image simulations of the James Webb Space Telescope's Near-Infrared Camera

## TL;DR

This paper introduces PhoSim-NIRCam, a physics-based photon-by-photon simulation tool for JWST's NIRCam, enabling detailed modeling of optical and detector effects crucial for precise astronomical measurements.

## Contribution

It adapts the PhoSim simulator for NIRCam, incorporating detailed physics to accurately replicate JWST observations and systematics.

## Key findings

- Simulates geometric aberration and diffraction effects.
- Provides full field- and wavelength-dependent PSFs.
- Generates realistic simulated images for validation.

## Abstract

Recent instrumentation projects have allocated resources to develop codes for simulating astronomical images. Novel physics-based models are essential for understanding telescope, instrument, and environmental systematics in observations. A deep understanding of these systematics is especially important in the context of weak gravitational lensing, galaxy morphology, and other sensitive measurements. In this work, we present an adaptation of a physics-based ab initio image simulator: The Photon Simulator (PhoSim). We modify PhoSim for use with the Near-Infrared Camera (NIRCam) -- the primary imaging instrument aboard the James Webb Space Telescope (JWST). This photon Monte Carlo code replicates the observational catalog, telescope and camera optics, detector physics, and readout modes/electronics. Importantly, PhoSim-NIRCam simulates both geometric aberration and diffraction across the field of view. Full field- and wavelength-dependent point spread functions are presented. Simulated images of an extragalactic field are presented. Extensive validation is planned during in-orbit commissioning.