Heating and Ionization of the Intergalactic Medium by an Early X‐Ray Background

Venkatesan, Aparna; Giroux, Mark L.; Shull, J. M.

doi:10.1086/323691

Cited by 171 publications

(214 citation statements)

References 58 publications

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“…Häring & Rix 2004) by gas accretion (Islam et al 2003). The inferred presence of pregalactic IMBHs and their associated accretion luminosity has been a source of intense speculation with regard to a mechanism for the reionization of the universe (e.g., Madau et al 2004;Ricotti & Ostriker 2004;Venkatesan et al 2001). Our results place these speculations on a sounder footing.…”

Section: Discussion and Future Workmentioning

confidence: 52%

Pregalactic Black Hole Formation with an Atomic Hydrogen Equation of State

Spaans¹,

Silk

2006

ApJ

151

180

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The polytropic equation of state of an atomic hydrogen gas is examined for primordial halos with baryonic masses of M h $ 10 7 Y10 9 M . For roughly isothermal collapse around 10 4 K, we find that line trapping of Ly (H i and He ii) photons causes the polytropic exponent to stiffen to values significantly above unity. Under the assumptions of zero H 2 abundance and very modest pollution by metals (<10 À4 solar), fragmentation is likely to be inhibited for such an equation of state. We argue on purely thermodynamic grounds that a single black hole of $(0.02Y0.003)M h can form at the center of a halo for z ¼ 10Y20 when the free-fall time is less than the time needed for a resonantly scattered Ly photon to escape from the halo. The absence of H 2 follows naturally from the high temperatures, >10 4 K, that are attained when Ly photons are trapped in the dense and massive halos that we consider. An H 2 -dissociating UV background is needed if positive feedback effects on H 2 formation from X-rays occur. The black holeYtoYbaryon mass fraction is suggestively close to what is required for these intermediate-mass black holes, of mass M BH $ 10 4 Y10 6 M , to act as seeds for forming the supermassive black holes of mass $0.001M spheroid found in galaxies today.

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Section: Discussion and Future Workmentioning

confidence: 52%

Pregalactic Black Hole Formation with an Atomic Hydrogen Equation of State

Spaans¹,

Silk

2006

ApJ

151

180

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“…If the gas temperature is fixed to the CMB temperature, then the Jeans mass, M j ¼ 10 6 M . If molecular hydrogen is available, then the Jeans mass before reionization is M j 0 $ 2:2 Â 10 3 ½w b =hðw m Þ 1:5 ð1 þ zÞ=10 for z < 150 (Venkatesan et al 2001). At z > 150, the electrons are thermally coupled to the CMB photons.…”

Section: Reionization and Small-scale Powermentioning

confidence: 99%

“…They suggest using a minimum mass that is much higher: M HRL min ðzÞ ¼ 10 8 ð1 þ zÞ=10 ½ À3=2 . On the other hand, if the first stars generated a significant flux of X-rays (Oh 2001), then this would have promoted molecular hydrogen formation (Haiman et al 2000;Venkatesan et al 2001;Cen 2002), thus lowering the minimum mass back to M j .…”

Section: Reionization and Small-scale Powermentioning

confidence: 99%

First‐Year Wilkinson Microwave Anisotropy Probe ( WMAP ) Observations: Determination of Cosmological Parameters

Spergel¹,

Verde²,

Peiris³

et al. 2003

ASTROPHYS J SUPPL S

9,797

500

7,512

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WMAP precision data enable accurate testing of cosmological models. We find that the emerging standard model of cosmology, a flat Ã-dominated universe seeded by a nearly scale-invariant adiabatic Gaussian fluctuations, fits the WMAP data. For the WMAP data only, the best-fit parameters are h ¼ 0:72 AE 0:05, b h 2 ¼ 0:024 AE 0:001, m h 2 ¼ 0:14 AE 0:02, ¼ 0:166 þ0:076 À0:071 , n s ¼ 0:99 AE 0:04, and 8 ¼ 0:9 AE 0:1. With parameters fixed only by WMAP data, we can fit finer scale cosmic microwave background (CMB) measurements and measurements of large-scale structure (galaxy surveys and the Ly forest). This simple model is also consistent with a host of other astronomical measurements: its inferred age of the universe is consistent with stellar ages, the baryon/photon ratio is consistent with measurements of the [D/H] ratio, and the inferred Hubble constant is consistent with local observations of the expansion rate. We then fit the model parameters to a combination of WMAP data with other finer scale CMB experiments (ACBAR and CBI), 2dFGRS measurements, and Ly forest data to find the model's best-fit cosmological parameters: WMAP's best determination of ¼ 0:17 AE 0:04 arises directly from the temperaturepolarization (TE) data and not from this model fit, but they are consistent. These parameters imply that the age of the universe is 13:7 AE 0:2 Gyr. With the Ly forest data, the model favors but does not require a slowly varying spectral index. The significance of this running index is sensitive to the uncertainties in the Ly forest.By combining WMAP data with other astronomical data, we constrain the geometry of the universe, tot ¼ 1:02 AE 0:02, and the equation of state of the dark energy, w < À0:78 (95% confidence limit assuming w ! À1). The combination of WMAP and 2dFGRS data constrains the energy density in stable neutrinos: h 2 < 0:0072 (95% confidence limit). For three degenerate neutrino species, this limit implies that their mass is less than 0.23 eV (95% confidence limit). The WMAP detection of early reionization rules out warm dark matter. Subject headings: cosmic microwave background -cosmological parameterscosmology: observations -early universe On-line material: color figure

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“…The free-free emission from the hot (T $ 10 6 10 8 K) SNR leads to soft X-ray emission. It has been suggested that positive feedback, in terms of molecular hydrogen formation, is possible if an early X-ray background builds up (Haiman et al 2000;Oh 2002;Venkatesan et al 2001;see, however, a counterargument by Machacek et al 2003). Population III supernova remnants are therefore among the most plausible X-ray sources in the early universe ).…”

Section: Supernov Va Feedbackmentioning

confidence: 99%

The Structure and Evolution of Early Cosmological HiiRegions

Kitayama

Yoshida

Susa

et al. 2004

ApJ

274

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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Heating and Ionization of the Intergalactic Medium by an Early X‐Ray Background

Cited by 171 publications

References 58 publications

Pregalactic Black Hole Formation with an Atomic Hydrogen Equation of State

Pregalactic Black Hole Formation with an Atomic Hydrogen Equation of State

First‐Year Wilkinson Microwave Anisotropy Probe ( WMAP ) Observations: Determination of Cosmological Parameters

The Structure and Evolution of Early Cosmological HiiRegions

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