ON LYMAN-LIMIT SYSTEMS AND THE EVOLUTION OF THE INTERGALACTIC IONIZING BACKGROUND
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We study the properties of self-shielding intergalactic absorption systems and their implications for the ionizing background. We find that cosmological simulations post-processed with detailed radiative transfer calculations generally are able to reproduce the observed abundance of Lyman-limit systems, and we highlight possible discrepancies between the observations and simulations. This comparison tests cosmological simulations at overdensities of ∼100. Furthermore, we show that the properties of Lyman-limit systems in these simulations, in simple semianalytic arguments, and as suggested by recent observations indicate that a small change in the ionizing emissivity of the sources would have resulted in a much larger change in the amplitude of the intergalactic H i-ionizing background (with this scaling strengthening with increasing redshift). This strong scaling could explain the rapid evolution in the Lyα forest transmission observed at z ≈ 6. Our calculations agree with the suggestion of simpler models that the comoving ionizing emissivity was constant or even increasing from z = 3 to 6. Our calculations also provide a more rigorous estimate than in previous studies for the clumping factor of intergalactic gas after reionization, which we estimate was ≈2–3 at z = 6.Keywords:
Lyman limit
Background radiation
Lyman-alpha forest
Dark Ages
Both galaxies and the intergalactic medium evolve dramatically between $z \approx 2$ and the present. These changes are coupled via galactic winds, cloud accretion, and ionizing radiation. Measurements of these interactions are critical for building a physical understanding of galaxy assembly. This paper reviews the role of starburst galaxies in heating, enriching, and ionizing the intergalactic medium. The strategies used to address these problems rely heavily on access to the rest-frame ultraviolet (UV) spectrum. Rather modest gains in UV sensitivity are shown to produce enormous gains in our ability to follow the very low-density gas dispersed by galactic winds and galaxy interactions. This leverage results from the sensitivity of absorption lines to low ionic columns and the very steep rise in the areal density of quasars toward fainter magnitudes.
Intergalactic dust
Lyman-alpha forest
Lyman limit
Ultraviolet
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It is now widely accepted that a population of intergalactic hydrogen clouds is responsible for the plethora of absorption lines seen at wavelengths shorter than Ly α emission in all high-z QSOs. The question of whether the comoving number density of such clouds evolves with redshift has been somewhat controversial. It is usually assumed that
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Lyman-alpha forest
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We study the properties of self-shielding intergalactic absorption systems and their implications for the ionizing background. We find that cosmological simulations post-processed with detailed radiative transfer calculations generally are able to reproduce the observed abundance of Lyman-limit systems, and we highlight possible discrepancies between the observations and simulations. This comparison tests cosmological simulations at overdensities of ∼100. Furthermore, we show that the properties of Lyman-limit systems in these simulations, in simple semianalytic arguments, and as suggested by recent observations indicate that a small change in the ionizing emissivity of the sources would have resulted in a much larger change in the amplitude of the intergalactic H i-ionizing background (with this scaling strengthening with increasing redshift). This strong scaling could explain the rapid evolution in the Lyα forest transmission observed at z ≈ 6. Our calculations agree with the suggestion of simpler models that the comoving ionizing emissivity was constant or even increasing from z = 3 to 6. Our calculations also provide a more rigorous estimate than in previous studies for the clumping factor of intergalactic gas after reionization, which we estimate was ≈2–3 at z = 6.
Lyman limit
Background radiation
Lyman-alpha forest
Dark Ages
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The absorption spectrum on the blue side of the Lyα emission line of high redshift quasars is generally proposed to be caused by the absorption of neutral hydrogen in isolated intergalactic clouds - the Lyα clouds, which have the primordial composition. Following some early suggestions, a simulation in this paper shows that a diffusely distributed baryonic intergalactic medium (IGM) left over from the primordial nucleosynthesis can also produce these forest-like absorption features on a quasar spectrum at the Lyα transition frequency. The observed Lyα forest spectra would thus be either seriously contaminated by the contribution from the diffuse medium or totally due to it
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Both galaxies and the intergalactic medium evolve dramatically between $z \approx 2$ and the present. These changes are coupled via galactic winds, cloud accretion, and ionizing radiation. Measurements of these interactions are critical for building a physical understanding of galaxy assembly. This paper reviews the role of starburst galaxies in heating, enriching, and ionizing the intergalactic medium. The strategies used to address these problems rely heavily on access to the rest-frame ultraviolet (UV) spectrum. Rather modest gains in UV sensitivity are shown to produce enormous gains in our ability to follow the very low-density gas dispersed by galactic winds and galaxy interactions. This leverage results from the sensitivity of absorption lines to low ionic columns and the very steep rise in the areal density of quasars toward fainter magnitudes.
Intergalactic dust
Lyman-alpha forest
Lyman limit
Ultraviolet
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The results of a search for diffuse neutral hydrogen "Gunn-Peterson" absorption, including possible absorption from any overdensity in the diffuse intergalactic medium, at low to moderate redshifts (z < 1.2) are discussed. The relatively low incidence of Lyα forest lines at these redshifts makes this work more straightforward than would be the case at higher redshifts. Criteria for the selection of QSO spectra leading to conservative estimates of Gunn-Peterson absorption are discussed, including the requirement that spectra shortward of the O VI λ1032 emission line be available. Thus, extrapolation of the continuum from longward to shortward of the Lyα emission line can be replaced by interpolation of the continuum in the spectral interval between Lyα and O VI emission.
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We present an updated version of the so-called Madau model for attenuation of the radiation from distant objects by intergalactic neutral hydrogen. First, we derive the distribution function of intergalactic absorbers from the latest observational statistics of the Lyα forest, Lyman-limit systems and damped Lyα systems. The distribution function reproduces the observed redshift evolution of the Lyα depression and the mean-free path of the Lyman continuum excellently and simultaneously. We then derive a set of analytic functions describing the mean intergalactic attenuation curve for objects at z > 0.5. The new model predicts less (or more) Lyα attenuation for z ≃ 3–5 (z > 6) sources through the usual broad-band filters relative to the original Madau model. This may cause a systematic difference in the photometric redshift estimates, which is, however, still small: about 0.05. Finally, we find a more than 0.5 mag overestimation of Lyman-continuum attenuation in the original Madau model at z > 3, which causes a significant overcorrection against direct observations of the Lyman continuum of galaxies.
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Abstract Measurement of the continuum beyond the L YMAN limit in the spectra of highly redshifted quasars allows to put upper limits to intergalactic neutral hydrogen which are comparable to those derived from the G UNN ‐P ETERSON ‐S CHEUER ‐S CHKLOWSKI test. The data apply to a weighted average of neutral hydrogen along the whole line of sight to the quasar, not to a small region around the quasar as in the GPSS test. Some conclusions are derived for a possible clumped component of neutral hydrogen in different F RIEDMAN models.
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view Abstract Citations (115) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A New Upper Limit on the Density of Generally Distributed Intergalactic Neutral Hydrogen Steidel, Charles C. ; Sargent, Wallace L. W. Abstract A new upper limit on the number density of generally distributed intergalactic neutral hydrogen is obtained based upon recent spectrophotometric observations of very high redshift QSOs coupled with high-resolution statistical studies of the Lyα forest in QSOs. The new limit, nH I(z = 0.0) < 9.0×10-14h100cm-3, is approximately 15 times smaller than the limit originally proposed by Gunn and Peterson. Publication: The Astrophysical Journal Pub Date: July 1987 DOI: 10.1086/184927 Bibcode: 1987ApJ...318L..11S Keywords: Density Distribution; Gas Density; Hydrogen; Intergalactic Media; Neutral Gases; Quasars; Astronomical Spectroscopy; Gas Ionization; Line Spectra; Lyman Alpha Radiation; Red Shift; Ultraviolet Radiation; Astrophysics; GALAXIES: INTERGALACTIC MEDIUM; QUASARS full text sources ADS | data products SIMBAD (1) NED (1)
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Lyman limit
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Both galaxies and the intergalactic medium evolve dramatically between $z \approx 2$ and the present. These changes are coupled via galactic winds, cloud accretion, and ionizing radiation. Measurements of these interactions are critical for building a physical understanding of galaxy assembly. This paper reviews the role of starburst galaxies in heating, enriching, and ionizing the intergalactic medium. The strategies used to address these problems rely heavily on access to the rest-frame ultraviolet (UV) spectrum. Rather modest gains in UV sensitivity are shown to produce enormous gains in our ability to follow the very low-density gas dispersed by galactic winds and galaxy interactions. This leverage results from the sensitivity of absorption lines to low ionic columns and the very steep rise in the areal density of quasars toward fainter magnitudes.
Intergalactic dust
Lyman-alpha forest
Lyman limit
Ultraviolet
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