A 2019 Cosmic UV/X-ray Background Model Update. (arXiv:1903.08657v1 [astro-ph.CO])

A 2019 Cosmic UV/X-ray Background Model Update. (arXiv:1903.08657v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Faucher-Giguere/0/1/0/all/0/1">Faucher-Giguere</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+_A%2E_C/0/1/0/all/0/1">C.-A.</a> (Northwestern University)

We present an updated model of the cosmic ionizing background from the UV to
the X-rays. Relative to our previous model (Faucher-Giguere et al. 2009), the
new model provides a better fit to a large number of up-to-date empirical
constraints, including: 1) new galaxy UV luminosity functions; 2) stellar
spectra including binary stars; 3) recent escape fraction measurements; 4) a
measurement of the non-ionizing UV background; 5) obscured and unobscured AGN;
6) measurements of the intergalactic HI and HeII photoionization rates at
z~0-6; and 7) the local X-ray background. In this model, AGN dominate the HI
ionizing background at z<3 and star-forming galaxies dominate it at higher redshifts. Combined with the large AGN contribution at low redshifts and the steeply declining AGN luminosity function beyond z~2, the slow evolution of the HI ionization rate inferred from the HI Lya forest requires an escape fraction from star-forming galaxies that increases strongly with redshift. Our new UV background model implies a best-fit escape fraction of 7% at z=3. We provide effective photoionization and photoheating rates calibrated to match the Planck 2018 reionization optical depth and recent constraints from the HeII Lya forest.

We present an updated model of the cosmic ionizing background from the UV to
the X-rays. Relative to our previous model (Faucher-Giguere et al. 2009), the
new model provides a better fit to a large number of up-to-date empirical
constraints, including: 1) new galaxy UV luminosity functions; 2) stellar
spectra including binary stars; 3) recent escape fraction measurements; 4) a
measurement of the non-ionizing UV background; 5) obscured and unobscured AGN;
6) measurements of the intergalactic HI and HeII photoionization rates at
z~0-6; and 7) the local X-ray background. In this model, AGN dominate the HI
ionizing background at z<3 and star-forming galaxies dominate it at higher
redshifts. Combined with the large AGN contribution at low redshifts and the
steeply declining AGN luminosity function beyond z~2, the slow evolution of the
HI ionization rate inferred from the HI Lya forest requires an escape fraction
from star-forming galaxies that increases strongly with redshift. Our new UV
background model implies a best-fit escape fraction of 7% at z=3. We provide
effective photoionization and photoheating rates calibrated to match the Planck
2018 reionization optical depth and recent constraints from the HeII Lya
forest.

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