Temperature of the Cosmic Gas
Radiation Heats the Intergalactic Gas
The radiation of star-forming galaxies and active galactic nuclei (AGN) ionizes and heats the gas in the intergalactic medium (IGM). We ran a large grid of 400 cosmological simulations that vary the evolution of the UV background radiation, each simulation results in different thermal and ionization histories of the IGM. The figure below illustrates the difference in the IGM temperatures from variation in the UV background models.
By performing a Markov Chain Monte Carlo (MCMC) analysis, we identified a well-constrained model for the UV background that reproduces the observed properties of the Lyman-alpha forest.
Evolution of the Temperature of Cosmic Gas
From our model for the radiation of the UV background, we infer the thermal evolution of the IGM. We find that the IGM experiences two periods of heating during hydrogen and helium reionization, each followed by a period of cooling due to the expansion of the Universe. An illustration of the temperature evolution obtained from our analysis is shown below.
