We present the results of observations taken with the X-shooter spectrograph devoted to the study of quasars at z ∼ 6. This paper focuses on the properties of metals at high redshift traced, in particular, by the C iv doublet absorption systems. Six objects were observed with resolutions ≃27 and 34 km s⁻¹ in the visual, and 37.5 and 53.5 km s⁻¹ in the near-infrared. We detected 102 C iv lines in the range: 4.35 < z < 6.2 of which 27 are above z ∼ 5. Thanks to the characteristics of resolution and spectral coverage of X-shooter, we could also detect 25 Si iv doublets associated with the C iv at z ≳ 5. The column density distribution function of the C iv line sample is observed to evolve in redshift for z ≳ 5.3, with respect to the normalization defined by low-redshift (1.5 < z < 4) C iv lines. This behaviour is reflected in the redshift evolution of the C iv cosmic mass density, $$\Omega _{\rm C\,{\small {IV}}}$$, of lines with column density in the range $$13.4 < \log N(\mathrm{C\,\small {IV}}) < 15$$, which is consistent with a drop of a factor of ∼2 for z ≳ 5.3. Considering only the stronger C iv lines ($$13.8 < \log N(\mathrm{C\,\small {IV}}) < 15$$), $$\Omega _{\rm C\,{\small {IV}}}$$ gently rises by a factor of ∼10 between z ≃ 6.2 and z ≃ 1.5 with a possible flattening towards z ∼ 0. The increase is well fitted by a power law: $$\Omega _{\rm C\,{\small {IV}}} = (2\pm 1)\times 10^{-8} [(1+z)/4]^{-3.1\pm 0.1}$$. An insight into the properties of the C iv absorbers and their evolution with redshift is obtained by comparing the observed column densities of associated C iv, Si iv and C ii absorptions with the output of a set of cloudy photoionization models. As already claimed by cosmological simulations, we find that C iv is a good tracer of the metallicity in the low-density intergalactic medium (IGM) gas at z ∼ 5-6 while at z ∼ 3 it arises in gas with overdensity δ ∼ 100.

Context. Absorption-line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, α, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations in α on cosmological scales. These variations may reach a fractional level of ≈ 10 ppm (parts per million). Aims. To test these claims we are conducting a Large Program of observations with the Very Large Telescope’s Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution (R ≈ 60 000) and high signal-to-noise ratio (S/N ≈ 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this programme, that of HE 2217−2818.Methods. We applied the many multiplet method to measure α in five absorption systems towards this quasar: z abs = 0.7866, 0.9424, 1.5558, 1.6279 , and 1.6919.Results. The most precise result is obtained for the absorber at z abs = 1.6919 where 3 Fe ii transitions and Al ii λ1670 have high S/N and provide a wide range of sensitivities to α. The absorption profile is complex with several very narrow features, and it requires 32 velocity components to be fitted to the data. We also conducted a range of tests to estimate the systematic error budget. Our final result for the relative variation in α in this system is Δα/α = +1.3 ± 2.4stat ± 1.0sys ppm. This is one of the tightest current bounds on α-variation from an individual absorber. A second, separate approach to the data reduction, calibration, and analysis of this system yielded a slightly different result of −3.8 ppm, possibly suggesting a larger systematic error component than our tests indicated. This approach used an additional 3 Fe ii transitions, parts of which were masked due to contamination by telluric features. Restricting this analysis to the Fe ii transitions alone and using a modified absorption profile model gave a result that is consistent with the first approach, Δα/α = +1.1 ± 2.6stat ppm. The four other absorbers have simpler absorption profiles, with fewer and broader features, and offer transitions with a narrower range of sensitivities to α. They therefore provide looser bounds on Δα/α at the ≳10 ppm precision level. Conclusions. The absorbers towards quasar HE 2217−2818 reveal no evidence of any variation in α at the 3-ppm precision level (1σ confidence). If the recently reported 10-ppm dipolar variation in α across the sky is correct, the expectation at this sky position is (3.2−5.4) ± 1.7 ppm depending on dipole model used. Our constraint of Δα/α = +1.3 ± 2.4stat ± 1.0sys ppm is not inconsistent with this expectation.

We present an accurate analysis of the H₂ absorption lines from the z_abs ∼ 2.4018 damped Lyα system towards HE 0027−1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme ‘The UVES large programme for testing fundamental physics’ to constrain the variation of proton-to-electron mass ratio, μ ≡ m_p/m_e. We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength-dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single- and two-component Voigt profiles to model the observed H₂ absorption profiles. We use both linear regression analysis and Voigt profile fitting where Δμ/μ is explicitly considered as an additional fitting parameter. The two-component model is marginally favoured by the statistical indicators and we get Δμ/μ = −2.5 ± 8.1_stat ± 6.2_sys ppm. When we apply the correction to the wavelength-dependent velocity drift, we find Δμ/μ = −7.6 ± 8.1_stat ± 6.3_sys ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous Δμ/μ measurements.

We analyze extant data of Al++, Al+ and other low ions with the aim of studying the ionization properties of Damped Ly alpha systems (DLAs) from the analysis of the ratio R(Al++/Al+) = N(Al++)/N(Al+). We find good correlations logN(Al+)-logN(Si+) and logN(Al+)-logN(Fe+) that we use to indirectly estimate N(Al+) from N(Si+) and/or N(Fe+) measurements. In this way we determine the ratio R(Al++/Al+) for a sample of 20 DLAs. Contrary to common belief, the ratio can attain relatively high values (up to 0.6), suggesting that gas of intermediate ionization state plays an important role in DLAs. On the other hand, the lack of any trend between abundance ratios, such as Si/H and Si/Fe, and R(Al++/Al+) indicates that abundances are not severely influenced by ionization effects. We find a logR(Al++/Al+) - logN(H I) anticorrelation that we use, in conjunction with idealized photoionization equilibrium calculations, to constrain the ionization properties and to predict ionization corrections in DLAs. We consider two possible origins for the species of low and intermediate ionization state: (1) neutral regions devoid of Al++ and/or (2) partially ionized, (Al++)-bearing regions. The logR(Al++/Al+) - logN(H I) anticorrelation can be naturally explained in terms of a two-region model with a soft, stellar-type ionizing radiation field. We present abundance ionization corrections for 14 elements of astrophysical interest derived with different types of ionizing spectra. For most of these elements the corrections are generally below measurements errors, contrary to the predictions of recent models presented in the literature. We briefly discuss the potential effects of inaccuracies of the Al recombination rates used in the photoionization calculations.Comment: 20 pages including 16 figures, accepted for publication in the Astrophysical Journal, Vol. 557, No. 1, Aug 10, 200

The effects of the dust on the determination of elemental abundances in damped Lyα (DLA) absorbers are investigated. Relations between the observed abundances measured in the gas phase and the overall abundances (gas plus dust) are derived as a function of dust-to-gas ratio, metallicity, element-to-element abundance pattern, average extinction coefficient of dust grains, and chemical composition of dust grains. A method is presented for determining dust-to-gas ratios, dust-to-metals ratios, and dust-corrected relative abundances in DLA absorbers by assuming dust of Galactic type and constant abundance ratios between iron-peak elements. The method is applied to a sample of 17 DLA absorbers with available Zn, Cr, and/or Fe measurements. The resulting dust-to-gas ratios are mostly distributed between 2% and 25% of the Galactic value, in good quantitative agreement with the results from reddening studies of QSOs with foreground DLA absorption. A correlation is found between dust-to-gas ratio and metallicity in DLA galaxies, with a typical dust-to-metals ratio of ≈ 60% of the Galactic value. The derived dust-to-metals ratios are then used to correct from the effects of dust the abundance ratios [Si/Fe], [S/Fe], [Ti/Fe], [Mn/Fe], and [Ni/Fe] available for a subsample of nine absorbers. The [α/Fe] ratios corrected from dust do not show the enhancement characteristic of metal-poor Galactic stars, but instead have essentially solar values, within ±0.2 dex. This suggests that the chemical history of DLA absorbers is different from that experienced by the Milky Way. Evidence that points to dwarf galaxies, rather than to spiral galaxies, as important contributors to the DLA phenomenon is summarized.

Detailed studies of damped and sub-damped Lyman α systems (DLAs), the galaxies probed by the absorption they produce in the spectra of background quasars, rely on identifying the galaxy responsible for the absorber with more traditional methods. Integral field spectroscopy provides an efficient way of detecting faint galaxies near bright quasars, further providing immediate redshift confirmation. Here, we report the detection of Hα emission from a DLA and a sub-DLA galaxy among a sample of six intervening quasar absorbers targeted. We derive F(Hα) = 7.7 ± 2.7 × 10⁻¹⁷ erg s⁻¹ cm⁻² (SFR = 1.8 ± 0.6 M_⊙ yr⁻¹) at impact parameter b= 25 kpc towards quasar Q0302 − 223 for the DLA at z_abs= 1.009 and F(Hα) = 17.1 ± 6.0 × 10⁻¹⁷ erg s⁻¹ cm⁻² (SFR = 2.9 ± 1.0 M_⊙ yr⁻¹) at b= 39 kpc towards Q1009 − 0026 for the sub-DLA at z_abs= 0.887. These results are in line with low star formation rates previously reported in the literature for quasar absorbers. We use the [N ii]λ 6585/Hα ratio to derive the H ii emission metallicities and compare them with the neutral gas H i absorption metallicities derived from high-resolution spectra. In one case, the absorption metallicity is actually found to be higher than the emission line metallicity. For the remaining objects, we achieve 3σ limiting fluxes of the order F(Hα) ∼ 10⁻¹⁷ erg s⁻¹ cm⁻² (corresponding to SFR ∼ 0.1 M_⊙ yr⁻¹ at z∼ 1 and ∼1 M_⊙ yr⁻¹ at z∼ 2), i.e. among the lowest that have been possible with ground-based observations. We also present two other galaxies associated with C iv systems and serendipitously discovered in our data.