RUBIX: A virtual telescope for mock-MUSE observations from cosmological hydrodynamical simulations

IFU observations deliver us spatially resolved spectra of galaxies. However cosmological hydrodynamical simulations give us properties of star, gas and dark matter particles and not directly spatially resolved spectra. To compare simulations and observations directly and to study galaxy evolution with the full power of observations and simulations, we have to bridge this gap. Our virtual telescope RUBIX (Reconstruction Using Bayesian Inference eXperiments) forward models simulated galaxies from hydrodynamical cosmological simulations into IFU observations and enables a direct comparison with IFU observations. It is a modular tool written in JAX and has currently support for IllustrisTNG and NIHAO but adding other data formats is easy and straight forward. It has predefined telescope configurations like MUSE and supports standard SSP spectral libraries. The code automatically parallelizes computations across multiple GPUs. With the performance improvements the compute time reduces from hours (current state-of-the-art code) to only seconds. This gives us the possibility to calculate thousands of mock-MUSE observations. Additionally, RUBIX leverages JAX's auto-differentiation capabilities, enabling not only forward modeling for classic comparison with MUSE datacubes but also enabling gradient computation through the entire pipeline, which promises significant advancements for techniques like simulation-based-inference and gradient-based reconstructions of observations.