Francesco Haardt

Radiative transfer in a clumpy Universe. 2. The Ultraviolet extragalactic background

We present a detailed calculation of the propagation of AGN-like ionizing radiation through the intergalactic space. We model the ionization state of absorbing clouds, and show that the universe will be more opaque above

The Assembly and Merging History of Supermassive Black Holes in Hierarchical Models of Galaxy Formation

4\,

Radiative Transfer in a Clumpy Universe. III. The Nature of Cosmological Ionizing Sources

Ryd than previously estimated. Singly ionized helium in \Lya forest clouds and Lyman-limit systems is found to be very efficient in reprocessing soft X-ray, helium-ionizing photons into ultraviolet, hydrogen-ionizing ones. We demonstrate that a significant fraction of the absorbed primary photons (emitted, e.g., by quasar sources) will be reradiated by the photoionized gas through \Lya line emission, two-photon continuum, and recombination continuum radiation. In the light of new data and recent studies, we also reassess the contribution of the QSOs observed in optical surveys to the UV extragalactic background, and find that the stochastic reprocessing of quasar Lyman continuum radiation by hydrogen and helium along the line of sight will significantly affect the amplitude, spectral shape, and fluctuations properties of the metagalactic flux. In a scenario in which QSOs are the primary source of ionizing photons in the universe, the integrated \HI \Lya emission at

X-ray spectra from two-phase accretion disks

z=0

A MODEL FOR THE X-RAY AND ULTRAVIOLET EMISSION FROM SEYFERT GALAXIES AND GALACTIC BLACK HOLES

from photoionized \Lya clouds and Lyman-limit systems is found to be at a level of less than 5\% of current observational limits on the far-UV extragalactic radiation flux. We show that

Supermassive black hole binaries in gaseous and stellar circumnuclear discs: orbital dynamics and gas accretion

J_{912}

GeV gamma-ray attenuation and the high-redshift UV background

increases from

COSMIC REIONIZATION AFTER PLANCK: COULD QUASARS DO IT ALL?

\approx 10^{-23} \uvunits

Interaction of massive black hole binaries with their stellar environment. I. Ejection of hypervelocity stars

at the present epoch to

The imprint of massive black hole formation models on the LISA data stream

\approx 5\times 10^{-22}\uvunits