The UV spectrum of HS 1700+6416

Fechner, C.; Reimers, D.; Songaila, A.; Simcoe, Robert A.; Rauch, M.; Sargent, W. L. W.

doi:10.1051/0004-6361:20054455

Cited by 12 publications

(39 citation statements)

References 50 publications

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“…In the vicinity of z = 1.7193, the η-values reach several hundreds due to a sharp decrease in the number of photons with energies E 4 Ryd in the ionizing continuum and, as a consequence, the impossibility to ionize He ii. At z = 1.1923, where the preferable SEDs return to the range detected between He ii/H i forest studies have shown a slow evolution of η toward smaller values at lower redshift, with the meanη ∼ 70 at z = 2.9 andη ∼ 40 at z = 2.0 (Zheng et al 2004;Fechner et al 2006). Our values are in line with these results.…”

Section: Discussionsupporting

confidence: 91%

Fluctuations of the intergalactic ionization field at redshiftz~ 2

Agafonova

Levshakov

Reimers

et al. 2013

A&A

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Aims. To probe the spectral energy distribution (SED) of the ionizing background radiation at z 2 and to specify the sources contributing to the intergalactic radiation field. Methods. The spectrum of a bright quasar HS 1103+6416 (z em = 2.19) contains five successive metal-line absorption systems at z abs = 1.1923, 1.7193, 1.8873, 1.8916, and 1.9410. The systems are optically thin and reveal multiple lines of different metal ions with the ionization potentials lying in the extreme ultraviolet (EUV) range (∼1 Ryd to ∼0.2 keV). For each system, the EUV SED of the underlying ionization field is reconstructed by means of a special technique developed for solving the inverse problem in spectroscopy.For the z abs = 1.8916 system, the analysis also involves the He i resonance lines of the Lyman series and the He i λ504 Å continuum, which are seen for the first time in any cosmic object except the Sun. Results. From one system to another, the SED of the ionizing continuum changes significantly, indicating that the intergalactic ionization field at z 2 fluctuates at the scale of at least Δ z ∼ 0.004. This is consistent with Δ z 0.01 estimated from He ii and H i Lyman-α forest measurements between the redshifts 2 and 3. A radiation intensity break by approximately an order of magnitude at E = 4 Ryd in SEDs restored for the z abs = 1.1923, 1.8873, 1.8916, and 1.9410 systems points to quasars as the main sources of the ionizing radiation. The SED variability is mostly caused by a small number of objects contributing at any given redshift to the ionizing background; at scales Δ z 0.05, the influence of local radiation sources becomes significant. A remarkable SED restored for the z abs = 1.7193 system, with a sharp break shifted to E ∼ 3.5 Ryd and a subsequent intensity decrease by ∼1.5 dex, indicates a source with comparable inputs of both hard (active galactic nuclei, AGN) and soft (stellar) radiation components. Such a continuum can be emitted by (ultra) luminous infrared galaxies, many of which reveal both a strong AGN activity and intense star formation in the circumnuclear regions.

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Section: Discussionsupporting

confidence: 91%

Fluctuations of the intergalactic ionization field at redshiftz~ 2

Agafonova

Levshakov

Reimers

et al. 2013

A&A

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“…3. Additionally, the metal lines predicted to arise in the FUSE spectral range (Fechner et al 2006b) are considered during the optimization procedure modifying the χ 2 -estimation (Eq. (1)):…”

Section: Hs 1700+6416mentioning

confidence: 99%

“…This peak is most likely due to strong interstellar C ii λ1036 absorption, which is not considered in the spectrum fit procedure. Furthermore, strong C iv absorption from the Lyman limit system at z = 2.3155 is expected in the UV, which is probably underpredicted (see Fechner et al 2006b). Therefore, we overestimate the amount of absorption due to He ii leading to unrealistically high values of η.…”

Section: Hs 1700+6416mentioning

confidence: 99%

Fluctuations of the intergalactic UV background towards two lines of sight

Fechner

Reimers²

2006

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Aims. We present a reanalysis of the He ii Lyα absorption towards the quasars HS 1700+6416 and HE 2347-4342 using new high S /N, optical observations.Methods. An alternative analysis method is applied, which fits the high quality, optical H i data directly to the He ii spectrum. The results are compared to those inferred from standard line profile analyses. This new method enables us to derive redshift scales characterizing the fluctuations of the column density ratio η. Results. We find η changing smoothly with redshift on typical scales of ∆z ∼ 0.01−0.03 corresponding to 8−24 h −1 Mpc comoving. The real length scales of variations of the column density ratio might be even larger, since part of the fluctuations may be caused by noise in the He ii data and by systematic effects due to the applied method. However, variations on small scales cannot be ruled out completely. For η variations on scales of a few Mpc an amplitude of about ±1.5 dex cannot be excluded. The data shows an apparent correlation between low η regions and the presence of metal line absorbers, which corresponds to the more general correlation of low η and strong H i absorption. Thermal line broadening is suggested as a probable explanation for this apparent correlation, since both fit methods would severely underestimate η for absorbers with N H i > ∼ 10 13 cm −2 if the line width was dominated by thermal broadening. Indeed, lines located close to the cut-off of the b(N) distribution yield lower column density ratios compared to the whole sample, in particular if high density absorbers are considered. We argue that the apparent correlation of η with the strength of the H i absorption is caused by insufficient consideration of thermal broadened lines by the standard analysis. As unbiased value of the column density ratio, we find η ∼ 80 in agreement with previous estimates.

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“…We repeated the calculations with different spectra for the ionising background. Using a modified Haardt & Madau spectrum where the helium edge is shifted to 3 Ryd, possibly due to the opacity of higher He ii Lyman series lines (Fechner et al 2006) or a background radiation mainly created by AGN as proposed by Mathews & Ferland (1987), resulted in density parameters that are within each others 1σ error intervals. Misinterpretations in the sample of narrow Lyman α lines could add another uncertainty.…”

Section: Photoionisation Calculationsmentioning

confidence: 99%

The baryon density at z = 0.9–1.9

Prause¹,

Reimers²,

Fechner³

et al. 2007

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Aims. We present an analysis of the Lyman α 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. Methods. 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, Clusters of Galaxies and the High Redshift Universe Observed in X-rays) spectrum. The WHIM is traced with broad Lyman α (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. Results. 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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The UV spectrum of HS 1700+6416

Cited by 12 publications

References 50 publications

Fluctuations of the intergalactic ionization field at redshiftz~ 2

Fluctuations of the intergalactic ionization field at redshiftz~ 2

Fluctuations of the intergalactic UV background towards two lines of sight

The baryon density at z = 0.9–1.9

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