Understand
We present improved synthesis models of the evolving spectrum of the UV/X-ray diffuse background, updating and extending our previous results.
- Five new main components are added to our radiative transfer code CUBA: (1) the sawtooth modulation of the background intensity from resonant line absorption in the Lyman series of cosmic hydrogen and helium; (2) the X-ray emission from obscured and unobscured quasars; (3) a piecewise parameterization of the distribution in redshift and column density of intergalactic absorbers that fits recent measurements of the mean free path of 1 ryd photons; (4) an accurate treatment of the photoionization structure of absorbers; and (5) the UV emission from star-forming galaxies at all redshifts.
- We provide tables of the predicted HI and HeII photoionization and photoheating rates for use, e.g., in cosmological hydrodynamics simulations of the Lya forest, and a new metallicity-dependent calibration to the UV luminosity density-star formation rate density relation.
- A "minimal cosmic reionization model" is also presented in which the galaxy UV emissivity traces recent determinations of the cosmic history of star formation, the luminosity-weighted escape fraction of hydrogen-ionizing radiation increases rapidly with lookback time, the clumping factor of the high-redshift intergalactic medium evolves following the results of recent hydrodynamic simulations, and Population III stars and miniquasars make a negligible contribution to the metagalactic flux.