The distribution of Lyman-alpha absorption lines in the spectra of six QSOs - Evidence for an intergalactic origin

Sargent, W. L. W.; Young, Patrick; Boksenberg, A.; Tytler, David

doi:10.1086/190644

Cited by 386 publications

(314 citation statements)

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“…The function is defined so as to satisfy cc (0; 0) ¼ 1. With large-scale velocity correlations (>1000 km s À1 ) expected to be absent or weak (Sargent et al 1980), the autocorrelation function (on scales of $100 km s À1 ) mostly measures the Ly line width and the weak small-scale clustering of Ly forest systems (e.g., Webb 1987;Rauch et al 1992). We apply the correlation analysis to the wavelength interval [3950,4614] 8 of the QSO in our sample with the smallest separation between its images, RX J0911.4+ 0551A and B.…”

Section: Global Differences Between the Spectramentioning

confidence: 99%

Expansion and Collapse in the Cosmic Web

Rauch

Becker

Viel

et al. 2005

ApJ

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We study the kinematics of the gaseous cosmic web at high redshift using Ly forest absorption in multiple QSO sight lines. Observations of the projected velocity shifts between Ly absorbers common to the lines of sight to a gravitationally lensed QSO and three more widely separated QSO pairs are used to directly measure the expansion of the cosmic web in units of the Hubble velocity, as a function of redshift and spatial scale. The lines of sight used span a redshift range from about 2 to 4.5 and represent transverse scales from the subkiloparsec range to about 300 h À1 70 physical kpc. Using a simple analytic model and a cosmological hydrodynamic simulation, we constrain the underlying three-dimensional distribution of expansion velocities from the observed line-of-sight distribution of velocity shear across the plane of the sky. The shape of the shear distribution and its width (14.9 km s À1 rms for a physical transverse separation of 61 h À1 70 kpc at z ¼ 2, 30.0 km s À1 for 261 h À1 70 kpc at z ¼ 3:6) are found to be in good agreement with the IGM undergoing large-scale motions dominated by the Hubble flow, making this one of the most direct observations possible of the expansion of the universe. However, modeling the Ly clouds with a simple ''expanding pancake'' model, the average expansion velocity of the gaseous structures causing the Ly forest in the lower redshift (z $ 2) smaller separation (61 kpc) sample appears about 20% lower than the local Hubble expansion velocity.In order to understand the observed velocity distribution further we investigated the statistical distribution of expansion velocities in cosmological Ly forest simulations. The mean expansion velocity in the (z $ 2, separation $ 60 kpc) simulation is indeed somewhat smaller than the Hubble velocity, as found in the real data. We interpret this finding as tentative evidence for some Ly forest clouds breaking away from the Hubble flow and undergoing the early stages of gravitational collapse. However, the distribution of velocities is highly skewed, and the majority of Ly forest clouds at all redshifts from 2 to 3.8 expand with super-Hubble velocities, typically about 5%-20% faster than the Hubble flow. This behavior is explained if most Ly forest clouds in the column density range typically detectable are expanding filaments that stretch and drain into more massive nodes. The significant difference seen in the velocity distributions between the high-and low-redshift samples may conceivably reflect actual peculiar deceleration, the differences in spatial scale, or our selecting higher densities at lower redshift for a given detection threshold for Ly forest lines.We also investigate the alternative possibility that the velocity structure of the general Ly forest could have an entirely different, local origin, as expected if the Ly forest were produced or at least significantly modified by galactic feedback, e.g., winds from star-forming galaxies at high redshift. However, we find no evidence that the observed distribution of veloc...

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Section: Global Differences Between the Spectramentioning

confidence: 99%

Expansion and Collapse in the Cosmic Web

Rauch

Becker

Viel

et al. 2005

ApJ

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“…Some studies find a lack of clustering (Sargent et al 1980 at 1.7 < z < 3.3; Rauch et al 1992 at z ∼ 3; Williger et al 1994 at z ∼ 4), while others find clustering at scales ∆v ≤ 350 km s −1 (Webb 1987 at 1.9 < z < 2.8; Hu et al 1995 at z ∼ 2.8; Kulkarni et al 1996 at z ∼ 1.9; Lu et al 1996 at z ∼ 3.7; Cristiani et al 1997 at z ∼ 3.3). Figure 12 shows the velocity correlation strength at ∆v < 4000 km s −1 .…”

Section: The Two-point Velocity Correlation Functionmentioning

confidence: 99%

“…In addition, the Lyα forest can be used to constrain cosmological parameters, such as the density parameter Ω and the baryon density Ω b , providing a test to current cosmological theories (Sargent et al 1980;Davé et al 1999;Impey et al 1999;Schaye et al 1999;Machacek et al 2000).…”

Section: Introductionmentioning

confidence: 99%

The Lyαforest at $\mathsf{1.5 < {\vec z} < 4}$

Kim¹,

Cristiani

D’Odorico³

2001

A&A

119

191

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Abstract. Using high resolution (R ∼ 45 000), high S/N (∼20-50) VLT/UVES data, we have analyzed the Lyα forest of 3 QSOs in the neutral hydrogen (H i) column density range NH i = 10 12.5−16 cm −2 at 1.5 < z < 2.4. We combined our results with similar high-resolution, high S/N data in the literature at z > 2.4 to study the redshift evolution of the Lyα forest at 1.5 < z < 4. We have applied two types of analysis: the traditional Voigt profile fitting and statistics on the transmitted flux. The results from both analyses are in good agreement: 1. The differential column density distribution function, f (NH i), of the Lyα forest shows little evolution in the column density range NH i = 10 12.5−14 cm −2 , f (NH i) ∝ N −β H i , with β ∼ 1.4-1.5 at 1.5 < z < 4 and with a possible increase of β to β ∼ 1.7 at z < 1.8. A flattening of the power law slope at lower column densities at higher z can be attributed to more severe line blending. A deficiency of lines with NH i > 10 14 cm −2 is more noticeable at lower z than at higher z. The one-point function and the two-point function of the flux confirm that strong lines do evolve faster than weak lines; 2. The line number density per unit redshift, dn/dz, at NH i = 10 13.64−16 cm −2 is well fitted by a single power law, dn/dz ∝ (1 + z) 2.19±0.27 , at 1.5 < z < 4. In combination with the HST results from the HST QSO absorption line key project, the present data indicate that a flattening in the number density evolution occurs at z ∼ 1.2. The line counts as a function of the filling factor at the transmitted flux F in the range 0 < F < 0.9 are constant in the interval 1.5 < z < 4. This suggests that the Hubble expansion is the main drive governing the forest evolution at z > 1.5 and that the metagalactic UV background changes more slowly than a QSO-dominated background at z < 2; 3. The observed cutoff Doppler parameter at the fixed column density NH i = 10 13.5 cm −2 , bc,13.5, shows a weak increase with decreasing z, with a possible local bc,13.5 maximum at z ∼ 2.9; 4. The two-point velocity correlation function and the step optical depth correlation function show that the clustering strength increases as z decreases; 5. The evolution of the mean H i opacity, τ H i, is well approximated by an empirical power law, τ H i ∝ (1+z) 3.34±0.17 , at 1.5 < z < 4; 6. The baryon density, Ω b , derived both from the mean H i opacity and from the one-point function of the flux is consistent with the hypothesis that most baryons (over 90%) reside in the forest at 1.5 < z < 4, with little change in the contribution to the density, Ω, as a function of z.

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“…The properties of the Ly-␣ forest came under increasing scrutiny, with the first systematic survey conducted several years later by Sargent et al ͑1980͒ demonstrating through the homogeneity of the observed properties of the absorbers their intergalactic origin, as opposed to being clouds ejected by the observed QSOs. Although limited by the resolution of the spectrograph, the measured velocity widths of the Ly-␣ features corresponded to gas temperatures of a few to several 10 4 K, characteristic photoionization temperatures for gas of a primordial composition, for which there is no significant cooling by metals.…”

Section: Introductionmentioning

confidence: 99%

The physics of the intergalactic medium

2009

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Intergalactic space is filled with a pervasive medium of ionized gas, the intergalactic medium ͑IGM͒. A residual neutral fraction is detected in the spectra of quasistellar objects at both low and high redshifts, revealing a highly fluctuating medium with temperatures characteristic of photoionized gas. The statistics of the fluctuations are well reproduced by numerical gravity-hydrodynamics simulations within the context of standard cosmological structure formation scenarios. Thus, the study of the IGM offers an opportunity to probe the nature of the primordial density fluctuations on scales unavailable to other methods. The simulations also suggest that the IGM is the dominant reservoir of baryons produced by the Big Bang, and so the principal source of the matter from which galaxies formed. The detection of metal systems within the IGM shows that it was enriched by evolved stars early in its history, demonstrating an intimate connection between galaxy formation and the IGM. A comprehensive review of the current understanding of the structure and physical properties of the IGM and its relation to galaxies is presented, concluding with comments on prospects for furthering the study of the IGM using future ground-based facilities and space-based experiments.

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The distribution of Lyman-alpha absorption lines in the spectra of six QSOs - Evidence for an intergalactic origin

Cited by 386 publications

References 0 publications

Expansion and Collapse in the Cosmic Web

Expansion and Collapse in the Cosmic Web

The Lyαforest at $\mathsf{1.5 < {\vec z} < 4}$

The physics of the intergalactic medium

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