Reionization of Hydrogen and Helium by Early Stars and Quasars

By J. Stuart B. Wyithe, Abraham Loeb. 2002

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We compute the reionization histories of hydrogen and helium caused by the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that reproduces all known properties of the quasar luminosity function at high redshifts. The less constrained properties of the ionizing radiation produced by stars are modeled with two free parameters: (i) a transition redshift, ztran, above which the stellar population is dominated by massive, zero-metallicity stars and below which it is dominated by a Scalo mass function; and (ii) the product of the escape fraction of stellar ionizing photons from their host galaxies and the star formation efficiency, fescf*. We constrain the allowed range of these free parameters at high redshifts on the basis of the lack of the H I Gunn-Peterson trough at z ≲ 6 and the upper limit on the total intergalactic optical depth for electron scattering, τes < 0.18, from recent cosmic microwave background (CMB) experiments. We find that quasars ionize helium by a redshift z ~ 4, but cannot reionize hydrogen by themselves before z ~ 6. A major fraction of the allowed combinations of fescf* and ztran leads to an early peak in the ionized fraction because of the presence of metal-free stars at high redshifts. This sometimes results in two reionization epochs, namely, an early H II or He III overlap phase followed by recombination and a second overlap phase. Even if early overlap is not achieved, the peak in the visibility function for scattering of the CMB often coincides with the early ionization phase rather than with the actual reionization epoch. Consequently, τes does not correspond directly to the reionization redshift. We generically find values of τes ≳ 7%, which should be detectable by the MAP satellite.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e31042755ec15d8f9b9f148f46e6af8cc175a770

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Citations in the corpus

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).”
Simulations of Early Structure Formation: Primordial Gas Clouds (2003, background): “Cen (2002) emphasized the positive impact of an early X-ray background on the formation of the first stars and discussed the possibility that the Universe could have been re-ionized at an early epoch by Population III objects alone (see also Wyithe & Loeb 2003a, 2003b).”
Observational Constraints on Cosmic Reionization (2006, background): “As shown by a number of semi-analytical works (e.g., Cen 2003a,b, Chiu et al. 2003, Wyithe & Loeb 2003, Haiman & Holder 2003), adding feedback from an early generation of galaxy formation, or adjusting star formation efficiency at z > 6− 10, will produce a prolonged, or multi-epoch reionization…”
RADIATIVE TRANSFER IN A CLUMPY UNIVERSE. IV. NEW SYNTHESIS MODELS OF THE COSMIC UV/X-RAY BACKGROUND (2011, background): “…in galactic and subgalactic systems may provide the additional ionizing flux needed at early times (e.g., Madau, Haardt, & Rees 1999; Gnedin 2000; Haehnelt et al. 2001; Wyithe & Loeb 2003; Meiksin 2005; Trac & Cen 2007; Faucher-Giguère et al. 2008a; Gilmore et al. 2009; Robertson et al. 2010).”
Probing the Ionization State of the Universe at z > 6 (2003, background): “Wyithe & Loeb (2003) suggested that the hydrogen in the IGM could have been reionized twice, and Cen (2003) argued that two phases of reionization are likely under a wide range of conditions.”
Self-regulated reionization (2006, background): “…studies suggest that the inclusion of halos subject to Jeans-mass filtering has a significant effect on the mean reionization history (Shapiro et al. 1994; Shapiro1995; Chiu & Ostriker 2000; Haiman & Holder 2003; Wyithe & Loeb 2003; Onken & Miralda-Escudé 2004; Furlanetto & Loeb 2005).”
The First Stars (2003, background): “It has been suggested that an early generation of very massive Population III stars, as predicted by numerical simulations (see Section 3), could naturally allow for a solution (Cen 2003a,b; Haiman & Holder 2003; Somerville & Livio 2003; Wyithe & Loeb 2003a,b).”
The VLT-FLAMES Survey of Massive Stars: Observations in the Galactic Clusters NGC 3293, NGC 4755 and NGC 6611 ⋆ (2005, background): “…(Bromm et al. 2002; Abel et al. 2002), and these “zero-metallicity” (or Population III) stars are considered to be prime candidates for the re-ionization of the Universe (e.g. Haehnelt et al. 2001; Wyithe & Loeb 2003) that may have happened at redshifts greater than six (Becker et al. 2001).”
FORMATION RATES OF POPULATION III STARS AND CHEMICAL ENRICHMENT OF HALOS DURING THE REIONIZATION ERA (2009, methodology): “Several models had been proposed (Venkatesan et al. 2003; Cen 2003; Wyithe & Loeb 2003; Hui & Haiman 2003; Stiavelli et al. 2004) and many of these included a significant contribution from first stars to τe.”
Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ∼ 6 Quasars. II. A Sample of 19 Quasars (2005, methodology): “Models that include feedback from the formation of the earliest, metal-free populations can generally fit both the Gunn-Peterson measurements at low redshift and a high CMB polarization measurement (e.g., Cen 2003a, b, Wyithe & Loeb 2003a, Haiman & Holder 2003, Melchiorri et al. 2005).”
IONIZING PHOTON ESCAPE FRACTIONS FROM HIGH-REDSHIFT DWARF GALAXIES (2008, background): “…has to be assumed that the product of star formation efficiency and hydrogen ionizing photon escape fraction is ≥ 0.01 (e.g. Gnedin 2000; Cen 2003a,b; Wyithe & Loeb 2003a,b; Venkatesan et al. 2003; Somerville et al. 2003; Chiu et al. 2003; Haiman & Holder 2003; Ciardi et al. 2003; Sokasian et al.…”
Simulating Cosmic Reionization at Large Scales I: the Geometry of Reionization (2005, background): “Over the years many analytical approaches to modelling reionization have been proposed (e.g. Shapiro et al. 1994; Haiman& Holder 2003; Wyithe & Loeb 2003; Furlanetto et al. 2004; Iliev et al. 2005a).”
The morphology of H ii regions during reionization (2006, background): “We do not know which objects reionized the Universe, although it is most likely that stellar sources produced the bulk of the ionizing photons (e.g. Wyithe & Loeb 2003).”
NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, unknown): “…models of the reionization process (e.g., Madau et al. 1999; Miralda-Escudé et al. 2000; Gnedin 2000; Barkana & Loeb 2001; Razoumov et al. 2002; Wyithe & Loeb 2003; Ciardi et al. 2003) highlighted the essential physics that give rise to the ionized intergalactic medium (IGM) at late times.”
Probing the cosmic reionization history and local environment of gamma‐ray bursts through radio dispersion (2003, methodology): “Various scenarios have been put forth to account for these observations which predict very c© 2003 RAS different histories for the evolution of the ionization fraction (e.g. Ciardi, Ferrara & White 2003, Cen 2003, Wyithe & Loeb 2003; see Miralda-Escude 2003, Haiman 2003 for reviews).”
ESCAPE FRACTION OF IONIZING PHOTONS DURING REIONIZATION: EFFECTS DUE TO SUPERNOVA FEEDBACK AND RUNAWAY OB STARS (2014, background): “…to ionizing photons in both the ultraviolet (UV) and X-ray bands but are generally believed to be sub-dominant to stellar sources (Haehnelt et al. 2001; Wyithe & Loeb 2003; Schirber & Bullock 2003; Faucher-Giguère et al. 2008; Cowie et al. 2009; Willott et al. 2010; Fontanot et al. 2014).”