Probing High‐Redshift Radiation Fields with Gamma‐Ray Absorption

Oh, S. Peng

doi:10.1086/320641

Cited by 31 publications

(46 citation statements)

References 45 publications

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“…An interesting possibility proposed by Haiman et al (2000) and Oh (2001) is that an early X-ray background could increase the number of free electrons in the IGM and promote the production of hydrogen molecules. Analytical estimates (Haiman et al 2000) and numerical simulations (Machacek et al 2003) indicate, however, that the net effect is mild and that the positive feedback by an X-ray background does not entirely compensate for the negative feedback effect due to photodissociating LW radiation unless unreasonably high X-ray intensities are assumed.…”

Section: Discussionmentioning

confidence: 99%

“…Radiation can produce either negative feedback, by dissociating molecular hydrogen via Lyman-Werner (LW) resonances (Dekel & Rees 1987;Haiman, Abel, & Rees 2000;Omukai & Nishi 1998, or positive feedback from X-rays, which can promote H 2 production by boosting the free-electron fraction in distant regions (Haiman, Rees, & Loeb 1996;Oh 2001). It is not clear whether negative or positive feedback dominates.…”

Section: Introductionmentioning

confidence: 99%

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Simulations of Early Structure Formation: Primordial Gas Clouds

Yoshida¹,

Abel²,

Hernquist³

et al. 2003

ApJ

561

729

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We use cosmological simulations to study the origin of primordial star-forming clouds in a ÃCDM universe, by following the formation of dark matter halos and the cooling of gas within them. To model the physics of chemically pristine gas, we employ a nonequilibrium treatment of the chemistry of nine species (e À , H, H + , He, He + , He ++ , H 2 , H þ 2 , H À ) and include cooling by molecular hydrogen. By considering cosmological volumes, we are able to study the statistical properties of primordial halos, and the high resolution of our simulations enables us to examine these objects in detail. In particular, we explore the hierarchical growth of bound structures forming at redshifts z % 25 30 with total masses in the range %10 5 10 6 M . We find that when the amount of molecular hydrogen in these objects reaches a critical level, cooling by rotational line emission is efficient, and dense clumps of cold gas form. We identify these '' gas clouds '' as sites for primordial star formation. In our simulations, the threshold for gas cloud formation by molecular cooling corresponds to a critical halo mass of %5 Â 10 5 h À1 M , in agreement with earlier estimates, but with a weak dependence on redshift in the range z > 16. The complex interplay between the gravitational formation of dark halos and the thermodynamic and chemical evolution of the gas clouds compromises analytic estimates of the critical H 2 fraction. Dynamical heating from mass accretion and mergers opposes relatively inefficient cooling by molecular hydrogen, delaying the production of star-forming clouds in rapidly growing halos. We also investigate the effect of photodissociating ultraviolet radiation on the formation of primordial gas clouds. We consider two extreme cases, first by including a uniform radiation field in the optically thin limit and second by accounting for the maximum effect of gas self-shielding in virialized regions. For radiation with Lyman-Werner band flux J > 10 À23 ergs s À1 cm À2 Hz À1 sr À1 , hydrogen molecules are rapidly dissociated, rendering gas cooling inefficient. In both the cases we consider, the overall effect can be described by computing an equilibrium H 2 abundance for the radiation flux and defining an effective shielding factor. Based on our numerical results, we develop a semianalytic model of the formation of the first stars and demonstrate how it can be coupled with large N-body simulations to predict the star formation rate in the early universe.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Simulations of Early Structure Formation: Primordial Gas Clouds

Yoshida¹,

Abel²,

Hernquist³

et al. 2003

ApJ

561

729

View full text Add to dashboard Cite

show abstract

“…[205,206]). As discussed by a number of authors [207,208,199], UV radiation fields with sufficient intensities to cause the reionization of the intergalactic medium (IGM) are also likely to induce appreciable gamma-ray absorption in sources at z 6 at observed energies in the multiGeV range, with a potentially important contribution from Pop III stars. Measurements of these effects can thus provide important cross-checks of current models of cosmic reionization, a unique probe of the evolving UV EBL during the era of early star formation, as well as a test for the existence of the yet hypothetical Pop III stars.…”

Section: Extragalactic Background Light and Intergalactic Magnetic Fimentioning

confidence: 99%

Gamma-ray burst science in the era of the Cherenkov Telescope Array

Inoue

Granot

O’Brien

et al. 2013

Astroparticle Physics

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We outline the science prospects for gamma-ray bursts (GRBs) with the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory operating at energies above few tens of GeV. With its low energy threshold, large effective area and rapid slewing capabilities, CTA will be able to measure the spectra and variability of GRBs at multi-GeV energies with unprecedented photon statistics, and thereby break new ground in elucidating the physics of GRBs, which is still poorly understood. Such measurements will also provide crucial diagnostics of ultra-high-energy cosmic ray and neutrino production in GRBs, advance observational cosmology by probing the high-redshift extragalactic background light and intergalactic magnetic fields, and contribute to fundamental physics by testing Lorentz invariance violation with high precision. Aiming to quantify these goals, we present some simulated observations of GRB spectra and light curves, together with estimates of their detection rates with CTA. Although the expected detection rate is modest, of order a few GRBs per year, hundreds or more high-energy photons per burst may be attainable once they are detected. We also address various issues related to following up alerts from satellites and other facilities with CTA, as well as follow-up observations at other wavelengths. The possibility of discovering and observing GRBs from their onset including short GRBs during a wide-field survey mode is also briefly discussed.

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“…Recent work, motivated by the WMAP results, has emphasized the potential significant contribution to the ionizing background at the earliest epochs (z $ 15) from accretion onto the seeds of would-be supermassive black holes (Madau et al 2004;Ricotti & Ostriker 2003). The soft X-rays emitted by these sources can partially ionize the IGM early on (Oh 2001;Venkatesan & Shull 2001).…”

Section: Introductionmentioning

confidence: 99%

A Limit from the X‐Ray Background on the Contribution of Quasars to Reionization

Dijkstra

Haiman

Loeb

2004

ApJ

155

199

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A population of black holes ( BHs) at high redshifts (z k 6) that contributes significantly to the ionization of the intergalactic medium (IGM) would be accompanied by the copious production of hard (k10 keV ) X-ray photons. The resulting hard X-ray background would redshift and be observed as a present-day soft X-ray background (SXB). Under the hypothesis that BHs are the main producers of reionizing photons in the high-redshift universe, we calculate their contribution to the present-day SXB. We find that accreting BHs with a hard spectrum (be it luminous quasars or their lower mass ''miniquasar'' counterparts) could not fully reionize the universe without saturating the unresolved component of the 0.5-2 keV SXB at the !2 level. Distant miniquasars that produce enough X-rays to only partially ionize the IGM to a level of at most x e $ 50% saturate the unresolved SXB by P1 . Improved determinations of the unresolved component of the SXB can provide a powerful constraint on the contribution of accreting BHs to partial or full reionization. Subject headingg s: cosmology: theory -intergalactic medium -quasars: general On-line material: color figure

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Probing High‐Redshift Radiation Fields with Gamma‐Ray Absorption

Cited by 31 publications

References 45 publications

Simulations of Early Structure Formation: Primordial Gas Clouds

Simulations of Early Structure Formation: Primordial Gas Clouds

Gamma-ray burst science in the era of the Cherenkov Telescope Array

A Limit from the X‐Ray Background on the Contribution of Quasars to Reionization

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