Early Reionization by Miniquasars

By P. Madau, Martin J. Rees, M. Volonteri, F. Haardt, S. Oh. 2003

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Motivated by the recent detection by the Wilkinson Microwave Anisotropy Probe of a large optical depth to Thomson scattering, implying a very early reionization epoch, we assess a scenario where the universe was reionized by "miniquasars" powered by intermediate-mass black holes (IMBHs), the remnants of the first generation of massive stars. Pregalactic IMBHs form within minihalos above the cosmological Jeans mass collapsing at z > 20, get incorporated through mergers into larger and larger systems, sink to the center as a result of dynamical friction, and accrete cold material. The merger history of dark halos and associated IMBHs is followed by Monte Carlo realizations of the merger hierarchy in a ΛCDM cosmology. Our model is based on the assumptions that quasar activity is driven by major mergers and nuclear IMBHs accrete at the Eddington rate a fraction of the gas in the merger remnant. The long dynamical frictional timescales leave many IMBHs "wandering" in galaxy halos after a minor merger. While seed IMBHs that are as rare as the 3.5 σ peaks of the primordial density field evolve largely in isolation, a significant number of BH binary systems will form if IMBHs populate the more numerous 3 σ peaks instead. In the case of rapid binary coalescence a fraction of IMBHs will be displaced from galaxy centers and ejected into the intergalactic medium (IGM) by the "gravitational rocket" effect, rather than accrete and shine as miniquasars. We show that, under a number of plausible assumptions for the amount of gas accreted onto IMBHs and their emission spectrum, miniquasars powered by IMBHs, and not their stellar progenitors, may be responsible for cosmological reionization at z ~ 15. Reionization by miniquasars with a hard spectrum may be more "economical" than stellar reionization, as soft X-rays escape more easily from the dense sites of star formation and travel farther than EUV radiation. Energetic photons will permeate the universe more uniformly, make the low-density diffuse IGM warm and weakly ionized prior to the epoch of reionization breakthrough, set an entropy floor, and reduce gas clumping. Future 21 cm observations may detect a preheated, weakly ionized IGM in emission against the cosmic microwave background.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/2deb8b4dd359241af0c89a1d419386715c6018a1

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Citations in the corpus

REIONIZATION AFTER PLANCK: THE DERIVED GROWTH OF THE COSMIC IONIZING EMISSIVITY NOW MATCHES THE GROWTH OF THE GALAXY UV LUMINOSITY DENSITY (2015, background): “Indeed, it is possible to imagine the existence of other populations of ionizing sources (e.g., Chen et al. 2003; Somerville et al. 2003; Hansen & Haiman 2004; Madau et al. 2004; Ricotti & Ostriker 2004; Ricotti et al. 2008), which even if speculative could also match current constraints.”
The aftermath of the first stars: massive black holes (2006, background): “…onto these black holes has important consequences for theories of the reionization of the Universe by miniquasars, as it is often assumed that accretion at the Eddington rate is achievable for miniquasars at redshifts z >∼ 15 (see Madau et al. 2004; Ricotti & Ostriker 2004; Kuhlen & Madau 2005).”
Radiative Transfer Simulations of Cosmic Reionization. I. Methodology and Initial Results (2006, background): “Progress on the theoretical front has mostly come from analytical and semianalytical modeling (e.g., Barkana & Loeb 2001, 2004; Cen 2003a, 2003b; Wyithe & Loeb 2003; Furlanetto et al. 2004; Madau et al. 2004; Ricotti & Ostriker 2004; Wyithe & Cen 2007).”
The First Cosmic Structures and Their Effects (2004, background): “Madau et al. (2004), for example, have shown that miniquasars powered by intermediate-mass black holes (the remnants of the first generation of massive stars) could produce a significant amount of ionizing photons at z > 15, under a number of plausible assumptions for the amount of gas accreted…”
ACCRETION ONTO THE FIRST STELLAR-MASS BLACK HOLES (2007, background): “…that accretion onto these black holes could power miniquasars has received a great deal of attention lately, since their radiation could have significantly increased the ionizing photon budget of the universe and extended the reionization process (Ricotti & Ostriker 2004; Madau et al. 2004).”
X-ray pre-ionization powered by accretion on the first black holes – I. A model for the WMAP polarization measurement (2003, background): “During galaxy mergers there is a non-negligible probability that one of the two merging BHs sitting in the bulge is expelled from the galaxy (cf. Madau et al. 2004).”
Quasars at z = 6: The Survival of the Fittest (2006, background): “In a cosmic volume, the seed holes typically evolve in isolation (cfr. Madau et al. 2004).”
Formation of supermassive black holes by direct collapse in pre-galactic haloes (2006, background): “Halos susceptible to the “bars within bars” instability represent high peaks in the field of density fluctuations (Tegmark et al. 1997; Madau et al. 2004).”
Rapid Growth of High-Redshift Black Holes (2005, background): “Madau et al. (2004) found that pregalactic quasars powered by MBHs forming in 3.5σ peaks will reionize the IGM if they accrete at the Eddington rate a mass of order 10−3 the mass of the host halo in every major merger.”
A Recoiling Supermassive Black Hole in the Quasar SDSS J092712.65+294344.0? (2008, background): “…for galaxy assembly and BH growth in the early universe, and would give rise to a population of interstellar and intergalactic BHs (e.g., Madau et al. 2004, Merritt et al. 2004, Madau & Quataert 2004, Haiman 2004, Yoo & Miralda-Escudé 2004, Volonteri & Perna 2005, Volonteri & Rees…”
Massive black hole seeds from low angular momentum material (2003, background): “Madau et al. (2003) discussed how a population of ‘mini-quasars’ like this might be responsible for reionizing the Universe at z re ∼ 15.”
GeV gamma-ray attenuation and the high-redshift UV background (2009, background): “Studies of the opacity of Lyα and other redshifted absorption lines place constraints on the emission of UV photons by probing the neutral fraction, and therefore the balance between photoionizations and recombinations (Haehnelt et al. 2001; Madau et al. 2004a).”
21 cm cosmology in the 21st century (2011, background): “In reality, of course, their evolution could be considerably more complex [69, 70].”