view Abstract Citations (1433) References (99) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiative Transfer in a Clumpy Universe. II. The Ultraviolet Extragalactic Background Haardt, Francesco ; Madau, Piero integrated ultraviolet flux arising from QSOs and/or hot, massive stars metal-producing young galaxies is likely responsible for maintaining the intergalactic diffuse gas and Lyα forest clouds highly ionized state. spectrum intensity of such UV...

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view Abstract Citations (757) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-Ray Spectra from Two-Phase Accretion Disks Haardt, Francesco ; Maraschi, Laura A model for the X-ray emission radio-quiet active galactic nuclei (AGNs) is considered. The X-rays are produced via inverse Compton (IC) in a hot corona embedding colder accretion disk. Soft thermal photons emitted by cold layer provide main source of cooling electrons corona. At same...

We present improved synthesis models of the evolving spectrum UV/X-ray diffuse background, updating and extending our previous results. Five new main components are added to radiative transfer code CUBA: (1) sawtooth modulation background intensity from resonant line absorption in Lyman series cosmic hydrogen helium; (2) X-ray emission obscured unobscured quasars; (3) a piecewise parameterization distribution redshift column density intergalactic absorbers that fits recent measurements mean...

We assess models for the assembly of supermassive black holes (SMBHs) at center galaxies that trace their hierarchical buildup far up in dark halo "merger tree." Motivated by recent discovery luminous quasars around redshift z ≈ 6—suggesting a very early epoch—and numerical simulations fragmentation primordial molecular clouds cold matter (CDM) cosmogonies, we assume first "seed" (BHs) had intermediate masses and formed (mini)halos collapsing ~ 20 from high-σ density fluctuations. As these...

The history of the transition from a neutral intergalactic medium (IGM) to one that is almost fully ionized can reveal character cosmological ionizing sources. We study evolution volume filling factors H II and He III regions in clumpy IGM discuss implications for rival reionization scenarios rapid decline observed at z≳3 space density optical radio-loud quasars large population star-forming galaxies recently discovered same epoch. hydrogen component highly inhomogeneous universe completely...

We assess a model of late cosmic reionization in which the ionizing background radiation arises entirely from high redshift quasars and other active galactic nuclei (AGNs). The low optical depth to Thomson scattering reported by Planck Collaboration pushes instantaneous down z=8.8^{+1.7}_{-1.4} greatly reduces need for significant Lyman-continuum emission at very early times. show that, if recent claims numerous population faint AGNs z=4-6 are upheld, inferred AGN comoving emissivity these...

Searching for distinctive signatures, which characterize different formation channels of binary black holes (BBHs), is a crucial step towards the interpretation current and future gravitational wave detections. Here, we investigate demography merging BBHs in young star clusters (SCs), are nursery massive stars. We performed 4 × 103N-body simulations SCs with metallicity Z = 0.002, initial fraction 0.4, fractal conditions, to mimic clumpiness star-forming regions. Our include novel...

Recent observations suggest that hydrogen reionization ends late ($z \simeq 6$) and proceeds quickly. We present here a new model of the meta-galactic UV/X-ray background (UVB) is consistent with this. It adopts most recent determinations ionizing emissivity due to stars AGN, as well HI absorber column density distribution. Another major improvement treatment intergalactic medium (IGM) opacity for photons able consistently capture transition from neutral an ionized IGM. Previous synthesis...

The presence of an obscuring torus around the nucleus a Seyfert galaxy, as supposed in popular unification scheme, can strongly modify X-ray spectrum for both type 1 and 2 galaxies. We study this problem by means Monte Carlo simulations, finding that, if is Compton-thick, it scatter at small angles significant fraction nuclear radiation, contribute to continuum galaxies above ∼ 10 keV, fluorescence iron line 6.4 keV. At large inclination column densities, attenuated photoabsorption Compton...

We compute the expected low-frequency gravitational wave signal from coalescing massive black hole (MBH) binaries at center of galaxies in a hierarchical structure formation scenario which seed holes intermediate mass form far up dark halo "merger tree." The merger history matter halos and associated MBHs is followed via cosmological Monte Carlo realizations hierarchy redshift z = 20 to present ΛCDM cosmology. get incorporated through mergers into larger structures, sink because dynamical...

view Abstract Citations (367) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Model for the X-Ray and Ultraviolet Emission from Seyfert Galaxies Galactic Black Holes Haardt, Francesco ; Maraschi, Laura Ghisellini, Gabriele We propose that X-ray emission radio-quiet active galactic nuclei black holes is due to Comptonization of soft thermal photons emitted by underlying accretion disk in localized structures (blobs). The power per unit area...

Motivated by the recent detection WMAP of a large optical depth to Thomson scattering -- implying very early reionization epoch we assess scenario where universe was reionized `miniquasars' powered intermediate-mass black holes (IMBHs), remnants first generation massive stars. Pregalactic IMBHs form within minihalos above cosmological Jeans mass collapsing at z=24, get incorporated through mergers into larger and systems, sink center owing dynamical friction, accrete cold material. The...

We present four X-ray/γ-ray spectra of Cyg X-1 observed in the hard ('low') state simultaneously by Ginga and GRO OSSE on 1991 June 6. The have almost identical spectral form but vary normalization within a factor 2. 3-30keV are well represented power laws with an energy index α ∼ 0.6 Compton reflection component including fluorescent Fe Kα corresponding to solid angle reflector ∼0.3 × 2π. These join smoothly range (≥50keV) then cut off above ∼150keV. overall can be modelled repeated...

The dynamics of two massive black holes in a rotationally supported nuclear disc 10^8 solar masses is explored using N-Body/SPH simulations. Gas and star particles are co-present the disc. Described by Mestel profile, has vertical support provided turbulence gas, stellar velocity dispersion. A primary hole 4 million placed at centre disc, while secondary set initially on an eccentric co-rotating orbit plane. Its mass 1 to 1, 4, 10 ratio, relative primary. With this choice, we mimic pairs...

We present new calculations of the evolving UV background out to epoch cosmological reionization and make predictions for amount GeV gamma-ray attenuation by electron-positron pair production. Our results are based on recent semi-analytic models galaxy formation, which provide dust-extinguished radiation field due starlight, empirical estimates contribution quasars. account reprocessing ionizing photons intergalactic medium. test whether our can reproduce at high redshift from flux decrement...

We consider super-critical accretion with angular momentum onto stellar-mass black holes as a possible mechanism for growing billion-solar-mass from light seeds at early times. use the radiatively inefficient "slim disk" solution—advective, optically thick flows that generalize standard geometrically thin disk model—to show how mildly super-Eddington intermittent may significantly ease problem of assembling first massive when universe was less than 0.8 Gyr old. Because low radiative...

Using high-resolution hydrodynamical simulations, we explore the spin evolution of massive dual black holes orbiting inside a circumnuclear disc, relic gas-rich galaxy merger. The spiral inwards from initially eccentric co- or counter-rotating coplanar orbits relative to disc's rotation, and accrete gas that is carrying net angular momentum. As hole mass grows, its changes in strength direction due gravito-magnetic coupling with small-scale accretion disc. We find spins loose memory their...

Coalescing massive black hole binaries (MBHBs) of |$10^{4-7}~\rm M_{\odot }$|⁠, forming in the aftermath galaxy mergers, are primary targets space mission LISA, Laser Interferometer Space Antenna. An assessment LISA detection prospects requires an estimate abundance and properties MBHBs that form evolve during assembly cosmic structures. To this aim, we employ a semi-analytic model to follow co-evolution within their host galaxies. We identify three major evolutionary channels driving...

ABSTRACT Pair instability (PI) and pulsational PI prevent the formation of black holes (BHs) with mass ≳60 M⊙ from single star evolution. Here, we investigate possibility that BHs in gap form via stellar mergers multiple mergers, facilitated by dynamical encounters young clusters. We analyse 104 simulations, run direct N-body code nbody6++gpu coupled population synthesis mobse. find up to ∼6 per cent all simulated have gap, depending on progenitor’s metallicity. This channel is strongly...

Young star clusters are the most common birth-place of massive stars and dynamically active environments. Here, we study formation black holes (BHs) binary (BBHs) in young clusters, by means 6000 N-body simulations coupled with population synthesis. We probe three different stellar metallicities (Z=0.02, 0.002 0.0002) two initial density regimes (density at half-mass radius $\rho_{\rm h}\ge{}3.4\times10^4$ $\ge{1.5\times10^2}$ M$_\odot$ pc$^{-3}$ dense loose respectively). Metal-poor tend to...

The rapid assembly of the massive black holes that power luminous quasars observed at $z \sim 6-7$ remains a puzzle. Various direct collapse models have been proposed to head-start hole growth from initial seeds with masses $\sim 10^5\,\rm M_\odot$, which can then reach billion solar mass while accreting Eddington limit. Here we propose an alternative scenario based on radiatively inefficient super-critical accretion stellar-mass embedded in gaseous circum-nuclear discs (CNDs) expected exist...

We compare cosmological hydrodynamical simulations combined with the homogeneous metagalactic UV background (UVB) of Haardt & Madau (hereafter HM2012) to observations Lyman α forest that are sensitive thermal and ionization state intergalactic medium (IGM). The transition from optically thick thin photoheating predicted by simple one-zone, radiative transfer model implemented HM2012 predicts a history is in remarkably good agreement observed rise IGM temperature at z ∼ 3 if we account for...

Intermediate mass black holes (IMBHs) in the range $10^2-10^5\,\mathrm{M_{\odot}}$ bridge gap between stellar (BHs) and supermassive BHs. Here, we investigate possibility that IMBHs form young star clusters via runaway collisions BH mergers. We analyze $10^4$ simulations of dense clusters, featuring up-to-date wind models prescriptions for core collapse (pulsational) pair instability. In our simulations, only 9 out 218 binary mergers, with a $\sim{}100-140$ M$_\odot$. This channel is...

Making use of the publicly available 1D photoionization hydrodynamics code ATES we set out to investigate combined effects specific planetary gravitational potential energy ( ϕ p ≡ GM / R ) and stellar X-ray extreme ultraviolet (XUV) irradiation F XUV on evaporation efficiency η moderately-to-highly irradiated gaseous planets, from sub-Neptunes through hot Jupiters. We show that (known) existence a threshold above which energy-limited thermal escape (i.e., ≃ 1) is unattainable can be...