Realistic simulations of the intergalactic medium CDS&E

University Of California-San Diego, La Jolla CA

Investigators

Abstract

The material that fills the vast spaces between galaxies (the Intergalactic Medium, or IGM) is surprisingly poorly understood. One primary method of investigating the IGM is through the light it absorbs from very distant very bright quasi-stellar objects (quasars), which show hundreds of measurable features at very specific wavelengths. Unfortunately, detailed computational work is still unable to reproduce key aspects of the IGM, all at the same time and using the same input parameters. This must mean that those simulations do not correctly represent the real Universe. This study attempts to correct this failing with a systematic investigation of the physics included in the numerical studies, and a rigorous delineation of the valid regions of the large parameter space to be investigated. The IGM makes hundreds of absorption lines in quasar spectra that are sensitive to the thermal history of the Universe, but, as noted, current numerical simulations cannot simultaneously match several key features. The discrepancy is too large to be due to observational errors, and is seen in multiple comparisons even when using different numerical methods. This research team has decades of experience observing the IGM and running high fidelity simulations, and is forced to conclude that the simulations simply do not correctly represent our Universe. Therefore, this project will search for a realistic representation of the IGM through four new types of simulation, including a new radiation transport solver, a high resolution large box simulation with parameterized feedback, the first ever simulation of the IGM with self-consistent 3D radiative transfer, and physically motivated simulations that explore a wide variety of other possible heat sources. All these results will be synthesized, parameterizing precisely how they change the appearance of the IGM, so as to select those parameter values that will faithfully generate observations of the IGM. The work should locate what is missing from our understanding of the IGM, and discover and specify simulations that can exactly reproduce the main physical processes in the IGM. It will lead to more accurate and robust estimates of the IGM temperature, density and ionization, the intensity of the ultraviolet background radiation, and the clustering of matter on small scales that is used to set limits on neutrino masses. All of the simulations and the generating codes will be publicly available. This team has a two decade record of integrating education and diversity into their core research. Undergraduate students will receive instruction in cosmology, astrophysics, spectroscopy, and simulations, and they will work with advanced software tools.