Evidence for Reionization at [ITAL][CLC]z[/CLC][/ITAL] ∼ 6: Detection of a Gunn-Peterson Trough in a [ITAL][CLC]z[/CLC][/ITAL] = 6.28 Quasar
R. H. BeckerXiaohui FanR. L. WhiteMichael A. StraussVijay K. NarayananRobert H. LuptonJames E. GunnJames AnnisNeta A. BahcallJ. BrinkmannAndrew J. ConnollyIstván CsabaiPaul C. CzarapataMamoru DoiTimothy M. HeckmanG. S. HennessyŽeljko IvezićG. R. KnappD. Q. LambTimothy A. McKayJeffrey A. MunnThomas NashRobert C. NicholJeffrey R. PierGordon T. RichardsDonald P. SchneiderChris StoughtonAlexander S. SzalayAniruddha R. ThakarDonald G. York
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We present moderate-resolution Keck spectroscopy of quasars at z = 5.82, 5.99, and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the Lyα absorption in the spectra of these quasars evolves strongly with redshift. To z ∼ 5.7, the Lyα absorption evolves as expected from an extrapolation from lower redshifts. However, in the highest-redshift object, SDSSp J103027.10+052455.0 (z = 6.28), the average transmitted flux is 0.0038 ± 0.0026 times that of the continuum level over 8450 Å < λ < 8710 Å (5.95 < zabs < 6.16), consistent with zero flux. Thus the flux level drops by a factor of greater than 150 and is consistent with zero flux in the Lyα forest region immediately blueward of the Lyα emission line, compared with a drop by a factor of ∼10 at zabs ∼ 5.3. A similar break is seen at Lyβ; because of the decreased oscillator strength of this transition, this allows us to put a considerably stronger limit, τeff > 20, on the optical depth to Lyα absorption at z = 6. This is a clear detection of a complete Gunn-Peterson trough, caused by neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen fraction in the intergalactic medium would result in an undetectable flux in the Lyα forest region. Therefore, the existence of the Gunn-Peterson trough by itself does not indicate that the quasar is observed prior to the reionization epoch. However, the fast evolution of the mean absorption in these high-redshift quasars suggests that the mean ionizing background along the line of sight to this quasar has declined significantly from z ∼ 5 to 6, and the universe is approaching the reionization epoch at z ∼ 6.Keywords:
Lyman-alpha forest
Lyman limit
One of the most sought-after signatures of reionization is a rapid increase in the ionizing background (usually measured through the Lyman-alpha optical depth toward distant quasars). Conventional wisdom associates this with the "overlap" phase when ionized bubbles merge, allowing each source to affect a much larger volume. We argue that this picture fails to describe the transition to the post-overlap Universe, where Lyman-limit systems absorb ionizing photons over moderate lengthscales (20-100 Mpc). Using an analytic model, we compute the probability distribution of the amplitude of the ionizing background throughout reionization, including both discrete ionized bubbles and Lyman-limit systems (parameterized by an attenuation length). We show that overlap does not by itself cause a rapid increase in the ionizing background or a rapid decrease in the mean Lyman-alpha transmission toward distant quasars. More detailed semi-numeric models support these conclusions. We argue that rapid changes should instead be interpreted as evolution in the attenuation length itself, which may or may not be directly related to overlap.
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We present an analysis of the Lyman alpha forests of five quasar spectra in the near UV. Properties of the intergalactic medium (IGM) at an intermediate redshift interval (0.9 < z < 1.9) are studied. The amount of baryons in the diffuse photoionised IGM and the warm-hot intergalactic medium (WHIM) are traced to get constraints on the redshift evolution of the different phases of the intergalactic gas. The baryon density of the diffuse IGM is determined with photoionisation calculations under the assumption of local hydrostatic equilibrium. We assume that the gas is ionised by a metagalactic background radiation with a Haardt & Madau (2001) spectrum. The WHIM is traced with broad Lyman alpha (BLA) absorption. The properties of a number of BLA detections are studied. Under the assumption of collisional ionisation equilibrium a lower limit to the baryon density could be estimated. It is found that the diffuse photoionised IGM contains at least 25% of the total baryonic matter at redshifts 1 < z < 2. For the WHIM a lower limit of 2.4% could be determined. Furthermore the data indicates that the intergalactic gas is in a state of evolution at z=1.5. We confirm that a considerable part of the WHIM is created between z=1 and z=2.
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Intervening intergalactic HeII λ304 absorption has so far been detected toward four high redshift quasars by HST and HUT. The quantitative interpretation of these data provides a measure of the ionization in the absorbing gas in the form of the ratio of residual HeII ions to HI atoms. Assuming a standard Big Bang helium abundance, this ratio can be used to derive a lower limit on the baryonic content of the Lyman forest without reference to the intensity of the ionizing background flux. It is shown that the HeII detections are consistent with the ionized component of the Lyman forest being a dominant carrier of baryonic matter at high redshift. If the detected HeII absorption is attributed exclusively to the known population of Lyman forest clouds with HI column densitiesNHI >∼ 1012 cm−2, then lower limits for the cosmological density of the Lyman forest of Ωbh75 >∼ 1 10−2 at 〈z〉 ' 2.4, and Ωbh75 >∼ 9 10−2 at 〈z〉 ' 3.0, are implied by the HUT and HST data, respectively. Both these lower limits are uncomfortably large compared to recent determinations of Ωb based on the D/H ratio in the forest clouds, but can be lowered by adding a contribution from more diffuse gas, either in the form of very low column density forest clouds or a uniform intergalactic medium. While good consistency between the HeII and D/H values of Ωb can be reached in the 〈z〉 ' 2.4 case in this way, the very strong HeII absorption seen at 〈z〉 ' 3.0 is only barely reconcilable with the D/H data. This suggests that the underlying assumption of photoionization equilibrium may not apply to HeII at this redshift, thereby providing further indirect evidence for HeII reionization occurring at z ' 2.9.
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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.
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We measure the large-scale cross-correlation of quasars with the Lyα forest absorption in redshift space, using ∼ 60000 quasar spectra from Data Release 9 (DR9) of the Baryon Oscillation Spectroscopic Survey (BOSS). The cross-correlation is detected over a wide range of scales, up to comoving separations r of 80 h−1Mpc. For r > 15 h−1Mpc, we show that the cross-correlation is well fitted by the linear theory prediction for the mean overdensity around a quasar host halo in the standard ΛCDM model, with the redshift distortions indicative of gravitational evolution detected at high confidence. Using previous determinations of the Lyα forest bias factor obtained from the Lyα autocorrelation, we infer the quasar bias factor to be bq = 3.64+0.13−0.15 at a mean redshift z = 2.38, in agreement with previous measurements from the quasar auto-correlation. We also obtain a new estimate of the Lyα forest redshift distortion factor, βF = 1.1±0.15, slightly larger than but consistent with the previous measurement from the Lyα forest autocorrelation. The simple linear model we use fails at separations r < 15h−1Mpc, and we show that this may reasonably be due to the enhanced ionization due to radiation from the quasars. We also provide the expected correction that the mass overdensity around the quasar implies for measurements of the ionizing radiation background from the line-of-sight proximity effect.
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We report the discovery of a further line of sight allowing detection of Lyα absorption by the intergalactic medium. A HST/STIS survey of 32 bright quasars selected from the Hamburg Quasar Surveys yielded one detection toward QSO 1157+3143 (). A 10 orbit follow-up spectrum reveals a UV spectrum significantly suppressed by two intervening Lyman limit systems at and 2.94, but with the continuum flux recovering sufficiently shortward of ~ to allow study of the absorption spectrum in the redshift range . The absorption is characterized by alternating voids and dense filament structures seen in both and . Attempts to model the opacity in terms of Lyα forest absorption are not successful in the voids, suggesting that reionization is not complete between and 2.97 or that an optically thin Lyman limit system with is responsible for the additional opacity.
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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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We use MUSE/VLT to conduct a survey of $z\sim3$ physical quasar pairs at close separation with a fast observation strategy. Our aim is twofold: (i) explore the Ly$\alpha$ glow around the faint-end of the quasar population; (ii) take advantage of the combined illumination of a quasar pair to unveil large-scale intergalactic structures extending between the two quasars. Here, we report the results for a quasar pair ($z=3.020,3.008$; $i=21.84,22.15$), separated by 11.6 arcsec (or 89 projected kpc). MUSE reveals filamentary Ly$\alpha$ structures extending between the two quasars with an average surface brightness of SB$_{\rm Ly\alpha}=1.8\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Photoionization models of the constraints in the Ly$\alpha$, HeII, and CIV line emissions show that the emitting structures are intergalactic bridges with an extent between $\sim89$ and up to $\sim600$ kpc. Our models rule out the possibility that the structure extends for $\sim 2.9$ Mpc, i.e., the separation inferred from the uncertain systemic redshift difference of the quasars if the difference was only due to the Hubble flow. At the current spatial resolution and surface brightness limit, the average projected width of an individual bridge is about 35 kpc. We also detect a strong absorption in HI, NV, and CIV along the background sight-line at higher $z$, which we interpret as due to at least two components of cool, metal enriched, and relatively ionized CGM or IGM surrounding the quasar pair. Two additional HI absorbers are detected along both quasar sight-lines at $\sim -900$ and $-2800$ km s$^{-1}$ from the system, with the latter having associated CIV absorption only along the foreground quasar sight-line. The absence of galaxies in the MUSE field of view at the redshifts of these two absorbers suggests that they trace large-scale structures or expanding shells in front of the quasar pair.
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view Abstract Citations (27) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effects of Intergalactic Absorption on the Visibility of Young Galaxies Yoshii, Yuzuru ; Peterson, Bruce A. Abstract Intergalactic H I clouds that produce the Ly伪 absorption lines in QSO spectra with rest-frame equivalent widths greater than about 0.5 A accumulate along the line of sight to be optically thick at wavelengths below the Lyman limit due to Lyman continuum absorption. Because the number of clouds along the line of sight increases rapidly with redshift, the cumulative effect of Lyman line absorption will also extinguish the spectra of source objects with a redshift of z_s_ > 5.5 that are observed at wavelengths below 位~8000 A before the Lyman limit eventually enters this wavelength region at z_s_ ~ 8. The intergalactic absorption places a definite upper bound on observable redshift of z_s_~ 5.5, above which no objects can be probed in optical surveys, either by spectroscopy or by I-band photometry. A question of whether galaxies would form at much earlier epoches can be answered only by searches at longer wavelengths where the intergalactic absorption is less. Publication: The Astrophysical Journal Pub Date: December 1994 DOI: 10.1086/174929 Bibcode: 1994ApJ...436..551Y Keywords: Absorption Spectra; Astronomical Models; Cosmology; H I Regions; Lyman Alpha Radiation; Molecular Clouds; Quasars; Stellar Spectra; Astronomical Photometry; Mathematical Models; Ultraviolet Astronomy; Astronomy; COSMOLOGY: OBSERVATIONS; GALAXIES: INTERGALACTIC MEDIUM; GALAXIES: PHOTOMETRY; ULTRAVIOLET: GALAXIES full text sources ADS | data products SIMBAD (1)
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