Cosmological H II regions and the photoionization of the intergalactic medium

Shapiro, Paul R.; Giroux, Mark L.

doi:10.1086/185015

Cited by 264 publications

(280 citation statements)

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“…The contribution of ultraviolet (UV) background radiation from quasars has been studied in a number of papers (e.g., Madau, Haardt, & Rees 1999;Donahue & Shull 1987;Shapiro & Giroux 1987;Bajtlik, Duncan, & Ostriker 1988), but quasars alone appear inadequate to produce enough UV radiation to reionize the IGM at high redshift because their number density declines steeply above z ¼ 3 (e.g., Fan et al 2001). On the other hand, a large number of starforming galaxies at 2dzd4 have recently been discovered using the Lyman break technique , and the inferred star formation rate is found to stay constant from z ¼ 1 up to at least $4 (Steidel et al 1999).…”

Section: Introductionmentioning

confidence: 99%

The Influence of Supershells and Galactic Outflows on the Escape of Ionizing Radiation from Dwarf Starburst Galaxies

Fujita

Martin

Low

et al. 2003

ApJ

115

145

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We study the escape of Lyman continuum radiation from the disks of dwarf starburst galaxies, with and without supershells, by solving the radiation transfer problem of stellar radiation through them. We model disks with M d ¼ 10 8 10 10 M , with exponential surface density profiles as a function of redshift, and model the effects of repeated supernova explosions driving supershells out of the disks, using the hydrodynamic simulation code ZEUS-3D. The amount of star formation is assumed proportional to mass above some density threshold. We vary the threshold to explore the range of star formation efficiencies, f Ã ¼ 0:006, 0.06, and 0.6. We find that the interstellar gas swept up in dense supershells can effectively trap the ionizing photons before the supershells blow out of the disks. The blowouts then create galactic outflows, chimneys that allow the photons to escape directly to the intergalactic medium. Our results are consistent with escape fractions of less than 0.1 measured in local dwarf starburst galaxies, because they are likely observed while the starbursts are young, before blowout. We suggest that high-redshift dwarf starburst galaxies may make a substantial contribution to the UV background radiation with total escape fractions e0.2, as expected if star formation efficiencies are e0:06.

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Section: Introductionmentioning

confidence: 99%

The Influence of Supershells and Galactic Outflows on the Escape of Ionizing Radiation from Dwarf Starburst Galaxies

Fujita

Martin

Low

et al. 2003

ApJ

115

145

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“…stars or collisionally ionized in large halos; see also Mesinger & Haiman 2004, or for a higher fraction Wyithe & Loeb 2004a), where hn H i i is the average proper number density of neutral hydrogen and hn H i is the density of total hydrogen. After the nuclear activity is triggered, the expansion of the ionization front (or the Strömgren sphere) in the rest frame of the QSO as a function of (not as a function of t A here) may be described by the following equation (e.g., Shapiro & Giroux 1987;Donahue & Shull 1987;Cen & Haiman 2000;Madau & Rees 2000;Yu & Lu 2005):…”

Section: Geometrymentioning

confidence: 99%

“…These highly ionized regions around the QSOs are generally idealized as spherical in the rest frame of the QSO and called Strömgren spheres. 2 The expansion of the Strömgren sphere depends on the QSO luminosity evolution and its environment (e.g., Shapiro & Giroux 1987;Donahue & Shull 1987). Observers on Earth perceive an object (here the highly ionized region) by the light reaching Earth at the same moment.…”

Section: Introductionmentioning

confidence: 99%

The Apparent Shape of the Stromgren Sphere around the Highest Redshift QSOs with Gunn‐Peterson Troughs

Yu¹

2005

ApJ

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Although the highest redshift QSOs (z > 6:1) are embedded in a significantly neutral background universe (mass-averaged neutral hydrogen fraction >1%) as suggested by the Gunn-Peterson absorption troughs in their spectra, the intergalactic medium in their vicinity is highly ionized. The highly ionized region is generally idealized as spherical and called the Strömgren sphere. In this paper, by combining the expected evolution of the Strömgren sphere with the rule that the speed of light is finite, we illustrate the apparent shape of the ionization fronts around the highest redshift QSOs and its evolution, which depends on the age, luminosity evolution, and environment of the QSO (e.g., the hydrogen reionization history). The apparent shape may systematically deviate from a spherical shape, unless the QSO age is significantly long compared to the hydrogen recombination process within the ionization front and the QSO luminosity evolution is significantly slow. Effects of anisotropy of QSO emission are also discussed. The apparent shape of the Strömgren sphere may be directly mapped by transmitted spectra of background sources behind or inside the ionized regions or by surveys of the hyperfine transition (21 cm) line emission of neutral hydrogen.

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“…Shu et al (2002) obtained the self-similar solutions for the expansion of self-gravitating H ii regions. On cosmological backgrounds, Shapiro & Giroux (1987) studied the evolution of the cosmological Strömgren sphere around luminous quasars in an expanding universe. Ricotti & Shull (2000) computed the UV photon consumption in small-mass halos to estimate the photon escape fraction.…”

Section: Introductionmentioning

confidence: 99%

The Structure and Evolution of Early Cosmological HiiRegions

Kitayama

Yoshida

Susa

et al. 2004

ApJ

276

322

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We study the formation and evolution of H ii regions around the first stars formed at redshifts z ¼ 10 30. We use a one-dimensional Lagrangian hydrodynamics code that self-consistently incorporates radiative transfer and nonequilibrium primordial gas chemistry. The star-forming region is defined as a spherical dense molecular gas cloud with a Population III star embedded at the center. We explore a large parameter space by considering, as plausible early star-forming sites, dark matter halos of mass M halo ¼ 10 5 10 8 M , gas density profiles with a power-law index w ¼ 1:5 2:25, and metal-free stars of mass M star ¼ 25 500 M . The formation of the H ii region is characterized by initial slow expansion of a weak D-type ionization front near the center, followed by rapid propagation of an R-type front throughout the outer gas envelope. We find that the transition between the two front types is indeed a critical condition for the complete ionization of halos of cosmological interest. In small-mass (P10 6 M ) halos, the transition takes place within a few 10 5 yr, yielding high escape fractions (>80%) of both ionizing and photodissociating photons. The gas is effectively evacuated by a supersonic shock, with the mean density within the halo decreasing to P1 cm À3 in a few million years. In larger mass (k10 7 M ) halos, the ionization front remains to be of D-type over the lifetime of the massive star, the H ii region is confined well inside the virial radius, and the escape fractions are essentially zero. We derive an analytic formula that reproduces well the results of our simulations for the critical halo mass below which the gas is completely ionized. We discuss immediate implications of the present results for the star formation history and early reionization of the universe.

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Cosmological H II regions and the photoionization of the intergalactic medium

Cited by 264 publications

References 0 publications

The Influence of Supershells and Galactic Outflows on the Escape of Ionizing Radiation from Dwarf Starburst Galaxies

The Influence of Supershells and Galactic Outflows on the Escape of Ionizing Radiation from Dwarf Starburst Galaxies

The Apparent Shape of the Stromgren Sphere around the Highest Redshift QSOs with Gunn‐Peterson Troughs

The Structure and Evolution of Early Cosmological HiiRegions

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