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1.
We present the results of a continuing survey to detect Lyα emitting galaxies at redshifts   z ∼ 9  : the ' z equals nine' (ZEN) survey. We have obtained deep VLT Infrared Spectrometer and Array Camera observations in the narrow J -band filter NB119 directed towards three massive lensing clusters: Abell clusters 1689, 1835 and 114. The foreground clusters provide a magnified view of the distant Universe and permit a sensitive test for the presence of very high redshift galaxies. We search for   z ∼ 9 Lyα  emitting galaxies displaying a significant narrow-band excess relative to accompanying J -band observations that remain undetected in Hubble Space Telescope ( HST )/Advanced Camera for Surveys (ACS) optical images of each field. No sources consistent with this criterion are detected above the unlensed 90 per cent point-source flux limit of the narrow-band image,   F NB= 3.7 × 10−18 erg s−1 cm−2  . To date, the total coverage of the ZEN survey has sampled a volume at   z ∼ 9  of approximately 1700 comoving Mpc3 to a Lyα emission luminosity of  1043 erg s−1  . We conclude by considering the prospects for detecting   z ∼ 9 Lyα  emitting galaxies in light of both observed galaxy properties at   z < 7  and simulated populations at   z > 7  .  相似文献   

2.
We measure the matter power spectrum from 31 Lyα spectra spanning the redshift range of 1.6–3.6. The optical depth, τ, for Lyα absorption of the intergalactic medium is obtained from the flux using the inversion method of Nusser & Haehnelt. The optical depth is converted to density by using a simple power-law relation,  τ∝ (1 +δ)α  . The non-linear 1D power spectrum of the gas density is then inferred with a method that makes simultaneous use of the one- and two-point statistics of the flux and compared against theoretical models with a likelihood analysis. A cold dark matter model with standard cosmological parameters fits the data well. The power-spectrum amplitude is measured to be (assuming a flat Universe),  σ8= (0.92 ± 0.09) × (Ωm/0.3)−0.3  , with α varying in the range of 1.56–1.8 with redshift. Enforcing the same cosmological parameters in all four redshift bins, the likelihood analysis suggests some evolution in the temperature–density relation and the thermal smoothing length of the gas. The inferred evolution is consistent with that expected if reionization of He  ii occurred at   z ∼ 3.2  . A joint analysis with the Wilkinson Microwave Anisotropy Probe results together with a prior on the Hubble constant as suggested by the Hubble Space Telescope key project data, yields values of Ωm and σ8 that are consistent with the cosmological concordance model. We also perform a further inversion to obtain the linear 3D power spectrum of the matter density fluctuations.  相似文献   

3.
We show that spatial correlations in a stochastic large-scale velocity field in an otherwise smooth intergalactic medium (homogeneous comoving density) superposed on the general Hubble flow may cause a 'line-like' structure in QSO spectra similar to the population of unsaturated Lyα forest lines which usually are attributed to individual clouds with 1011 ≲ N H i  5 × 1013 cm−2. Therefore there is no clear observational distinction between a diffuse intergalactic medium and discrete intergalactic clouds. It follows that the H  i density in the diffuse intergalactic medium might be substantially underestimated if it is determined from the observed intensity distribution near the apparent continuum in high-resolution spectra of QSOs. Our tentative estimate implies a diffuse neutral hydrogen opacity τGP ∼ 0.3 at z  ∼ 3 and a current baryon density ΩIGM ≃ 0.08, assuming a Hubble constant H 0 = 70 km s−1 Mpc−1.  相似文献   

4.
Three independent observational studies have now detected a narrow  (Δ z ≃ 0.5)  dip centred at   z = 3.2  in the otherwise smooth redshift evolution of the Lyα forest effective optical depth. This feature has previously been interpreted as an indirect signature of rapid photoheating in the intergalactic medium (IGM) during the epoch of He  ii reionization. We examine this interpretation using a semi-analytic model of inhomogeneous He  ii reionization and high-resolution hydrodynamical simulations of the Lyα forest. We instead find that a rapid  (Δ z ≃ 0.2)  boost to the IGM temperature  (Δ T ≃ 104 K)  beginning at   z = 3.4  produces a well understood and generic evolution in the Lyα effective optical depth, where a sudden reduction in the opacity is followed by a gradual, monotonic recovery driven largely by adiabatic cooling in the low-density IGM. This behaviour is inconsistent with the narrow feature in the observational data. If photoheating during He  ii reionization is instead extended over several redshift units, as recent theoretical studies suggest, then the Lyα opacity will evolve smoothly with redshift. We conclude that the sharp dip observed in the Lyα forest effective optical depth is instead most likely due to a narrow peak in the hydrogen photoionization rate around   z = 3.2  , and suggest that it may arise from the modulation of either reprocessed radiation during He  ii reionization, or the opacity of Lyman limit systems.  相似文献   

5.
Using cosmological hydrodynamic simulations, we measure the mean transmitted flux in the Lyα forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel quasar separation distance can be fitted using a simple power-law form including the usual correlation function parameters r 0 and γ, so that     . From the simulations, we find the relation between r 0 and quasar host mass, and formulate this as a way to estimate quasar host dark matter halo masses, quantifying uncertainties due to cosmological and IGM parameters, and redshift errors. With this method, we examine data for ∼9000 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 5, assuming that the effect of ionizing radiation from quasars (the so-called transverse proximity effect) is unimportant (no evidence for it is seen in the data). We find that the best-fitting host halo mass for SDSS quasars with mean redshift z = 3 and absolute G -band magnitude −27.5 is  log  M /M⊙= 12.68+0.81−0.67  . We also use the Lyman-Break Galaxy (LBG) and Lyα forest data of Adelberger et al. in a similar fashion to constrain the halo mass of LBGs to be  log10  M /M⊙= 11.41+0.54−0.59  , a factor of ∼20 lower than the bright quasars. In addition, we study the redshift distortions of the Lyα forest around quasars, using the simulations. We use the quadrupole to monopole ratio of the quasar Lyα forest correlation function as a measure of the squashing effect. We find its dependence on halo mass difficult to measure, but find that it may be useful for constraining cosmic geometry.  相似文献   

6.
We present a sample of 33 damped Lyman α systems (DLAs) discovered in the Sloan Digital Sky Survey (SDSS) whose absorption redshifts ( z abs) are within 6000 km s−1 of the quasi-stellar object's (QSO) systemic redshift ( z sys). Our sample is based on  731 2.5 < z sys < 4.5  non-broad absorption line (non-BAL) QSOs from Data Release 3 (DR3) of the SDSS. We estimate that our search is ≈100 per cent complete for absorbers with N (H  i )  ≥ 2 × 1020 cm−2  . The derived number density of DLAs per unit redshift, n ( z ), within  Δ v < 6000 km s−1  is higher (3.5σ significance) by almost a factor of 2 than that of intervening absorbers observed in the SDSS DR3, i.e. there is evidence for an overdensity of galaxies near the QSOs. This provides a physical motivation for excluding DLAs at small velocity separations in surveys of intervening 'field' DLAs. In addition, we find that the overdensity of proximate DLAs is independent of the radio-loudness of the QSO, consistent with the environments of radio-loud and radio-quiet QSOs being similar.  相似文献   

7.
The Voigt–Hjerting function is fundamental in order to correctly model the profiles of absorption lines imprinted on the spectra of bright background sources by intervening absorbing systems. In this work, we present a simple analytic approximation to this function in the context of absorption-line profiles of intergalactic H  i absorbers. Using basic calculus tools, we derive an analytic expression for the Voigt–Hjerting function that contains only fourth-order polynomial and Gaussian functions. In connection with the absorption coefficient of intergalactic neutral hydrogen, this approximation is suitable for modelling Voigt profiles with an accuracy of 10−4 or better for an arbitrary wavelength baseline, for column densities up to   N H I= 10 22 cm−2  , and for damping parameters   a ≲ 10−4  , that is, the entire range of parameters characteristic to all Lyman transitions arising in a variety of H  i absorbing systems such as Lyman α (Lyα) forest clouds, Lyman limit systems and damped Lyα systems. We hence present an approximation to the Voigt–Hjerting function that is both accurate and flexible to implement in various types of programming languages and machines, and with which Voigt profiles can be calculated in a reliable and very simple manner.  相似文献   

8.
We report the Giant Metrewave Radio Telescope detection of H  i 21-cm absorption from the z ∼ 3.39 damped Lyman α absorber (DLA) towards PKS 0201+113, the highest redshift at which 21-cm absorption has been detected in a DLA. The absorption is spread over ∼115 km s−1 and has two components, at   z = 3.387 144(17)  and   z = 3.386 141  (45). The stronger component has a redshift and velocity width in agreement with the tentative detection of Briggs, Brinks & Wolfe, but a significantly lower optical depth. The core size and DLA covering factor are estimated to be ≲100 pc and f ∼ 0.69, respectively, from a Very Long Baseline Array 328-MHz image. If one makes the conventional assumption that the H  i column densities towards the optical and radio cores are the same, this optical depth corresponds to a spin temperature of T s∼[(955 ± 160) × ( f /0.69)] K. However, this assumption may not be correct, given that no metal-line absorption is seen at the redshift of the stronger 21-cm component, indicating that this component does not arise along the line of sight to the optical quasi-stellar object (QSO), and that there is structure in the 21-cm absorbing gas on scales smaller than the size of the radio core. We model the 21-cm absorbing gas as having a two-phase structure with cold dense gas randomly distributed within a diffuse envelope of warm gas. For such a model, our radio data indicate that, even if the optical QSO lies along a line of sight with a fortuitously high (∼50 per cent) cold gas fraction, the average cold gas fraction is low, ≲17 per cent, when averaged over the spatial extent of the radio core. Finally, the large mismatch between peak 21-cm and optical redshifts and the complexity of both profiles makes it unlikely that the z ∼ 3.39 DLA will be useful in tests of fundamental constant evolution.  相似文献   

9.
We report on a further analysis of the ratio of deuterium to hydrogen (D/H) using Hubble Space Telescope ( HST ) spectra of the   z = 0.701  Lyman limit system towards the quasi-stellar object (QSO) PG1718+481. Initial analyses of this absorber found it gave a high D/H value, 1.8–  3.1 × 10−4  , inconsistent with several higher redshift measurements. It is thus important to critically examine this measurement. By analysing the velocity widths of the D  i , H  i and metal lines present in this system, Kirkman et al. report that the additional absorption in the blue wing of the Lyα line cannot be D  i , with a confidence level of 98 per cent. Here we present a more detailed analysis, taking into account possible wavelength shifts between the three sets of HST spectra used in the analysis. We find that the constraints on this system are not as strong as those claimed by Kirkman et al. The discrepancy between the parameters of the blue wing absorption and the parameters expected for D  i is marginally worse than 1σ.
Tytler et al. commented on the first analysis of Webb et al., reporting the presence of a contaminating lower redshift Lyman limit system, with  log[ N (H  i )] = 16.7  at   z = 0.602  , which biases the N (H  i ) estimate for the main system. Here we show that this absorber actually has  log[ N (H  i )] < 14.6  and does not impact on the estimate of N (H  i ) in the system of interest at   z = 0.701  .
The purpose of the present paper is to highlight important aspects of the analysis which were not explored in previous studies, and hence to help refine the methods used in future analyses of D/H in quasar spectra.  相似文献   

10.
Motivated by recent observational studies of the environment of   z ∼ 6  QSOs, we have used the Millennium Run (MR) simulations to construct a very large  (∼4°× 4°)  mock redshift survey of star-forming galaxies at   z ∼ 6  . We use this simulated survey to study the relation between density enhancements in the distribution of i 775-dropouts and Lyα emitters, and their relation to the most massive haloes and protocluster regions at   z ∼ 6  . Our simulation predicts significant variations in surface density across the sky with some voids and filaments extending over scales of 1°, much larger than probed by current surveys. Approximately one-third of all   z ∼ 6  haloes hosting i -dropouts brighter than   z = 26.5  mag  (≈ M *UV, z =6)  become part of   z = 0  galaxy clusters. i -dropouts associated with protocluster regions are found in regions where the surface density is enhanced on scales ranging from a few to several tens of arcminutes on the sky. We analyse two structures of i -dropouts and Lyα emitters observed with the Subaru Telescope and show that these structures must be the seeds of massive clusters in formation. In striking contrast, six   z ∼ 6  QSO fields observed with Hubble Space Telescope show no significant enhancements in their i 775-dropout number counts. With the present data, we cannot rule out the QSOs being hosted by the most massive haloes. However, neither can we confirm this widely used assumption. We conclude by giving detailed recommendations for the interpretation and planning of observations by current and future ground- and space-based instruments that will shed new light on questions related to the large-scale structure at   z ∼ 6  .  相似文献   

11.
We announce the discovery of an extended emission-line region associated with a high-redshift type-2 quasi-stellar object (QSO). The halo, which was discovered in our new wide-field narrow-band survey, resides at   z = 2.85  in the Spitzer First Look Survey region and is extended over ∼80 kpc. Deep very long baseline interferometry (VLBI) observations imply that approximately 50 per cent of the radio emission is extended on scales >200 pc. The inferred active galactic nuclei (AGN) luminosity is sufficient to ionize the extended halo, and the optical emission is consistent with being triggered coevally with the radio source. The Lyα halo is as luminous as those found around high-redshift radio galaxies; however, the active nucleus is several orders of magnitude less luminous at radio wavelengths than those Fanarof–Riley type II (FRIIs) more commonly associated with extended emission-line regions. AMS05 appears to be a high-redshift analogue to the radio-quiet quasar E1821+643 which is core dominated, but which also exhibits extended Fanarof–Riley type I (FRI)-like structure and contains an optically powerful AGN. We also find evidence for more quiescent kinematics in the Lyα emission line in the outer regions of the halo, reminiscent of the haloes around the more powerful FRIIs. The optical to mid-infrared spectral energy distribution is well described by a combination of an obscured QSO  ( L bol∼ 3.4 ± 0.2 × 1013 L⊙)  and a 1.4 Gyr old simple stellar population with mass  ∼3.9 ± 0.3 × 1011 M⊙  .  相似文献   

12.
We analyse the transmitted flux in a sample of 17 QSOs spectra at 5.74 ≤ z em≤ 6.42 to obtain tighter constraints on the volume-averaged neutral hydrogen fraction, x H  i , at z ≈ 6. We study separately the narrow transmission windows (peaks) and the wide dark portions (gaps) in the observed absorption spectra. By comparing the statistics of these spectral features with a semi-analytical model of the Lyα forest, we conclude that x H  i evolves smoothly from 10−4.4 at   z = 5.3  to 10−4.2 at   z = 5.6  , with a robust upper limit x H  i < 0.36 at   z = 6.3  . The frequency and physical sizes of the peaks imply an origin in cosmic underdense regions and/or in H  ii regions around faint quasars or galaxies. In one case (the intervening H  ii region of the faint quasar RD J1148+5253 at   z = 5.70  along the line of sight of SDSS J1148+5251 at   z = 6.42  ) the increase of the peak spectral density is explained by the first-ever detected transverse proximity effect in the H  i Lyα forest; this indicates that at least some peaks result from a locally enhanced radiation field. We then obtain a strong lower limit on the foreground QSO lifetime of t Q > 11 Myr. The observed widths of the peaks are found to be systematically larger than the simulated ones. Reasons for such discrepancy might reside either in the photoionization equilibrium assumption or in radiative transfer effects.  相似文献   

13.
The z  = 2.286  IRAS galaxy F10214 + 4724 remains one of the most luminous galaxies in the Universe, despite its gravitational lens magnification. We present optical and near-infrared spectra of F10214 + 4724, with clear evidence for three distinct components: lines of width ∼ 1000 km s−1 from a Seyfert 2 nucleus; ≲ 200 km s−1 lines which are likely to be associated with star formation; and a broad (∼ 4000 km s−1) C  III ] 1909-Å emission line which is blueshifted by ∼ 1000 km s−1 with respect to the Seyfert 2 lines. Our study of the Seyfert 2 component leads to several new results. (i) From the double-peaked structure in the Lyα line, and the lack of Lyβ, we argue that the Lyα photons have emerged through a neutral column of N H ∼ 2.5 × 1025 m−2, possibly located within the AGN narrow-line region, as proposed for several high-redshift radio galaxies. (ii) The resonant O  VI 1032, 1036-Å doublet (previously identified as Lyβ) is in an optically thick (1:1) ratio. At face value this implies an extreme density ( n e ∼ 1017 m−3) more typical of broad-line region clouds. However, we attribute this instead to the damping wings of Lyβ from the resonant absorption. (iii) A tentative detection of He  II 1086 suggests little extinction in the rest frame ultraviolet.  相似文献   

14.
We present a measurement of the probability distribution function (PDF) of the transmitted flux in the Lyman α (Lyα) forest from a sample of 3492 quasars included in the Sloan Digital Sky Survey data release 3 (SDSS DR3). Our intention is to investigate the sensitivity of the Lyα flux PDF as measured from low-resolution and low signal-to-noise ratio data to a number of systematic errors such as uncertainties in the mean flux, continuum and noise estimate. The quasar continuum is described by the superposition of a power law and emission lines. We perform a power-law continuum fitting on a spectrum-by-spectrum basis, and obtain an average continuum slope of  αν= 0.59 ± 0.36  in the redshift range  2.5 < z < 3.5  . We take into account that the variation in the continuum indices increases the mean flux by 3 and 7 per cent at   z = 3  and 2.4, respectively, as compared to the values inferred with a single (mean) continuum slope. We compare our measurements to the PDF obtained with mock lognormal spectra, whose statistical properties have been constrained to match the observed Lyα flux PDF and power spectrum of high-resolution data. Using our power-law continuum fitting and the SDSS pipeline noise estimate yields a poor agreement between the observed and mock PDFs. Allowing for a break in the continuum slope and, more importantly, for residual scatter in the continuum level substantially improves the agreement. A decrease of ∼10–15 per cent in the mean quasar continuum with a typical rms variance at the 20 per cent level can account for the data, provided that the noise excess correction is no larger than ≲10 per cent.  相似文献   

15.
We present the spectra, positions, and finding charts for 31 bright ( R <19.3) colour-selected quasars covering the redshift range z =3.85–4.78, with four having redshifts z >4.5. The majority are in the southern sky ( δ <−25°). The quasar candidates were selected for their red ( B J− R ≳2.5) colours from UK or POSSII Schmidt Plates scanned at the Automated Plate Measuring (APM) facility in Cambridge. Low-resolution (≳ 10 Å) spectra were obtained to identify the quasars, primarily at the Las Campanas Observatory. The highest redshift quasar in our survey is at z ≈4.8 ( R =18.7) and its spectrum shows a damped Ly α absorption system at z =4.46. This is currently the highest redshift damped Ly α absorber detected. Five of these quasars exhibit intrinsic broad absorption line features. Combined with the previously published results from the first part of the APM United Kingdom Schmidt Telescope (UKST) survey we have now surveyed a total of ∼8000 deg2 of sky i.e. 40 per cent of the high galactic latitude (| b |>30°) sky, resulting in 59 optically selected quasars in the redshift range 3.85 to 4.78; 49 of which have z ≥4.00.  相似文献   

16.
We present a catalogue of 147 serendipitous X-ray sources selected to have hard spectra ( α <0.5) from a survey of 188 ROSAT fields. Such sources must be the dominant contributors to the X-ray background at faint fluxes. We have used Monte Carlo simulations to verify that our technique is very efficient at selecting hard sources: the survey has 10 times as much effective area for hard sources as it has for soft sources above a 0.5–2 keV flux level of 10−14 erg cm−2 s−1. The distribution of best-fitting spectral slopes of the hard sources suggests that a typical ROSAT hard source in our survey has a spectral slope α ∼0. The hard sources have a steep number flux relation (d N /d S ∝ S − γ with a best-fitting value of γ =2.72±0.12) and make up about 15 per cent of all 0.5–2 keV sources with S >10−14 erg cm−2 s−1. If their N ( S ) continues to fainter fluxes, the hard sources will comprise ∼40 per cent of sources with 5×10−15< S <10−14 erg cm−2 s−1. The population of hard sources can therefore account for the harder average spectra of ROSAT sources with S <10−14 erg cm−2 s−1. They probably make a strong contribution to the X-ray background at faint fluxes and could be the solution to the X-ray background spectral paradox.  相似文献   

17.
We have conducted a submillimetre mapping survey of faint, gravitationally lensed sources, where we have targeted 12 galaxy clusters and additionally the New Technology Telescope (NTT) Deep Field. The total area surveyed is 71.5 arcmin2 in the image plane; correcting for gravitational lensing, the total area surveyed is 40 arcmin2 in the source plane for a typical source redshift z ≈ 2.5. In the deepest maps, an image plane depth of 1σ rms ∼0.8 mJy is reached. This survey is the largest survey to date to reach such depths. In total 59 sources were detected, including three multiply imaged sources. The gravitational lensing makes it possible to detect sources with flux density below the blank field confusion limit. The lensing-corrected fluxes range from 0.11 to 19 mJy. After correcting for multiplicity, there are 10 sources with fluxes <2 mJy of which seven have submJy fluxes, doubling the number of such sources known. Number counts are determined below the confusion limit. At 1 mJy, the integrated number count is  ∼104 deg−2  , and at 0.5 mJy it is  ∼2 × 104 deg−2  . Based on the number counts, at a source plan flux limit of 0.1 mJy, essentially all of the 850-μm background emission has been resolved. The dominant contribution (>50 per cent) to the integrated background arises from sources with fluxes S 850 between 0.4 and 2.5 mJy, while the bright sources S 850 > 6 mJy contribute only 10 per cent.  相似文献   

18.
We use high-resolution hydrodynamical simulations to investigate the spatial correlation between weak  ( N H  i < 1015 cm−2)  Lyα absorbers and gas-rich galaxies in the local Universe. We confirm that Lyα absorbers are preferentially expected near gas-rich galaxies and that the degree of correlation increases with the column density of the absorber. The real-space galaxy auto-correlation is stronger than the cross-correlation (correlation lengths   r 0,gg= 3.1 ± 0.1 Mpc  h −1  and   r 0,ag= 1.4 ± 0.1 Mpc  h −1  , respectively), in contrast with the recent results of Ryan-Weber, and the auto-correlation of absorbers is very weak. These results are robust to the presence of strong galactic winds in the hydrodynamical simulations. In redshift space, a further mismatch arises since at small separations the distortion pattern of the simulated galaxy–absorber cross-correlation function is different from the one measured by Ryan-Weber. However, when sampling the intergalactic medium along a limited number of lines-of-sight, as in the real data, uncertainties in the cross-correlation estimates are large enough to account for these discrepancies. Our analysis suggests that the statistical significance of difference between the cross-correlation and auto-correlation signal in current data sets is ∼1σ only.  相似文献   

19.
We present time-series echelle spectra of the Paβ line of the T Tauri star SU Aur, observed over three consecutive nights. The line shows strong variability (∼10 per cent) over the velocity range 100–420 km s−1 in the red broad absorption component, and weaker variability (∼2 per cent) over the velocity range  −200–0 km s−1  in the blue wing. The variability in the velocity range  −200–0 km s−1  is correlated with that in  200–400 km s−1  , and the variability in these velocity ranges anticorrelates with that in  0–100 km s−1  . The mean spectrum from the second night shows the suggestion of a blueshifted absorption component at about  −150 km s−1  , similar to that found in the Hα and Hβ lines. We find the position of the subpeak in the red absorption component changes steadily with time, and its motion modulates at half the rotational period. We also find that the modulation of the line equivalent width is possibly associated with a half and a third of the rotational period, which is consistent with the surface Doppler images of SU Aur. Radiative transfer models of a rotationally modulated Paβ line, produced in the shock-heated magnetospheric accretion flow, are also presented. Models with a magnetic dipole offset reproduce the overall characteristics of the observed line variability, including the line equivalent width and the motion of the subpeak in the red absorption trough.  相似文献   

20.
Many models of early structure formation predict a period of heating immediately preceding reionization, when X-rays raise the gas temperature above that of the cosmic microwave background. These X-rays are often assumed to heat the intergalactic medium (IGM) uniformly, but in reality will heat the gas more strongly closer to the sources. We develop a framework for calculating fluctuations in the 21-cm brightness temperature that originate from this spatial variation in the heating rate. High-redshift sources are highly clustered, leading to significant gas temperature fluctuations (with fractional variations ∼40 per cent, peaking on   k ∼ 0.1 Mpc−1  scales). This induces a distinctive peak-trough structure in the angle-averaged 21-cm power spectrum, which may be accessible to the proposed Square Kilometre Array. This signal reaches the ∼10 mK level, and is stronger than that induced by Lyα flux fluctuations. As well as probing the thermal evolution of the IGM before reionization, this 21-cm signal contains information about the spectra of the first X-ray sources. Finally, we consider disentangling temperature, density and Lyα flux fluctuations as functions of redshift.  相似文献   

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