A cosmic UV/X-ray background model update

We present an updated model of the cosmic ionizing background from the UV to the X-rays. Relative to our previous model, the new model provides a better match to a large number of up-to-date empirical constraints, including: (1) new galaxy and AGN luminosity functions; (2) stellar spectra including binary stars; (3) obscured and unobscured AGN; (4) a measurement of the non-ionizing UV background; (5) measurements of the intergalactic H I and He II photoionization rates at z similar to 0-6; (6) the local X-ray background; and (7) improved measurements of the intergalactic opacity. In this model, AGN dominate the H ionizing background at z less than or similar to 3 and star-forming galaxies dominate it at higher redshifts. Combined with the steeply declining AGN luminosity function beyond z similar to 2, the slow evolution of the H I ionization rate inferred from the high-redshift HI Ly alpha forest requires an escape fraction from star-forming galaxies that increases with redshift (a population-averaged escape fraction of approximate to 1 per cent suffices to ionize the intergalactic medium at z = 3 when including the contribution from AGN). We provide effective photoionization and photoheating rates calibrated to match the Planck 2018 reionization optical depth and recent constraints from the He II Ly alpha forest in hydrodynamic simulations.