Abstract. Development of fundamental physics relies on the constancy of various fundamental quantities such as the finestructure constant. Detecting or constraining the possible time variations of these fundamental physical quantities is an important step toward a complete understanding of basic physics. High-quality absorption lines seen in the spectra of distant QSOs allow one to probe time variations of several of these quantities. Here we present the results from a detailed manymultiplet analysis, to detect the possible variation of the fine-structure constant, performed using high signal-to-noise ratio, (∼70 per pixel), high spectral resolution (R ≥ 45 000) observations of 23 Mg  systems detected toward 18 QSOs in the redshift range 0.4 ≤ z ≤ 2.3 obtained using UVES at the VLT. We validate our procedure and define the selection criteria that will avoid possible systematics using a detailed analysis of a simulated data set. The spectra of Mg  doublets and Fe  multiplets are generated considering variations in α and specifications identical to that of our UVES spectra. We show that our Voigt profile fitting code recovers the variation in α very accurately when we use single component systems and multiple-component systems that are not heavily blended. Spurious detections are frequently seen when we use heavily blended systems or systems with very weak lines. Thus we avoided these system while analysing the UVES data. To make the analysis transparent and accessible to the community for critical scrutiny, all the steps involved in the analysis are presented in detail. The weighted mean value of the variation in α obtained from our analysis over the redshift range 0.4 ≤ z ≤ 2.3 is ∆α/α = (−0.06 ± 0.06) × 10 −5 . The median redshift of our sample is 1.55 and corresponds to a look-back time of 9.7 Gyr in the most favored cosmological model today. The 3σ upper limit on the time variation of α is −2.5 × 10 −16 yr −1 ≤ (∆α/α∆t) ≤ +1.2 × 10 −16 yr −1 . To our knowledge this is the strongest constraint from quasar absorption line studies to till date.

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We study the clustering properties of metals in the intergalactic medium (IGM) as traced by 619 C iv and 81 Si iv absorption components with N≥ 1012 cm−2 and 316 Mg ii and 82 Fe ii absorption components with N≥ 1011.5 cm−2 in 19 high signal‐to‐noise ratio (60–100 pixel−1), high‐resolution (R= 45 000) quasar spectra. C iv and Si iv trace each other closely and their line‐of‐sight correlation functions ξ(v) exhibit a steep decline at large separations and a flatter profile below ≈150 km s−1, with a large overall bias. These features do not depend on absorber column densities, although there are hints that the overall amplitude of ξC iv (v) increases with time over the redshift range detected (1.5–3). Carrying out a detailed smoothed particle hydrodynamic simulation (2 × 3203, 57 Mpc3 comoving), we show that the C iv correlation function cannot be reproduced by models in which the IGM metallicity is constant or a local function of overdensity (Z∝Δ2/3). However, the properties of ξC iv(v) are generally consistent with a model in which metals are confined within bubbles with a typical radius Rs about sources of mass ≥Ms. We derive best‐fitting values of Rs≈ 2 comoving Mpc and Ms≈ 1012 M⊙ at z= 3. Our lower‐redshift (0.5–2) measurements of the Mg ii and Fe ii correlation functions also uncover a steep decline at large separations and a flatter profile at small separations, but the clustering is even higher than in the z= 1.5–3 measurements, and the turnover is shifted to somewhat smaller distances, ≈75 km s−1. Again, these features do not change with column density, but there are hints that the amplitudes of ξMg ii(v) and ξFe ii(v) increase with time. We describe an analytic ‘bubble’ model for these species, which come from regions that are too compact to be accurately simulated numerically, deriving best‐fitting values of Rs≈ 2.4 Mpc and Ms≈ 1012 M⊙. Equally good analytic fits to all four species are found in a similarly biased high‐redshift enrichment model in which metals are placed within 2.4 comoving Mpc of Ms≈ 3 × 109 sources at z= 7.5.

Abstract. A new limit on the possible cosmological variation of the proton-to-electron mass ratio µ = m p /m e is estimated by measuring wavelengths of H 2 lines of Lyman and Werner bands from two absorption systems at z abs = 2.5947 and 3.0249 in the spectra of quasars Q 0405−443 and Q 0347−383, respectively. Data are of the highest spectral resolution (R = 53 000) and S/N ratio (30÷70) for this kind of study. We search for any correlation between z i , the redshift of observed lines, determined using laboratory wavelengths as references, and K i , the sensitivity coefficient of the lines to a change of µ, that could be interpreted as a variation of µ over the corresponding cosmological time. We use two sets of laboratory wavelengths, the first one, Set (A) (Abgrall et al. 1993, J. Mol. Spec., 157, 512), based on experimental determination of energy levels and the second one, Set (P) (Philip et al. 2004, Can. J. Chem., 82, 713), based on new laboratory measurements of some individual rest-wavelengths. We find ∆µ/µ = (3.05 ± 0.75) × 10 −5 for Set (A), and ∆µ/µ = (1.65 ± 0.74) × 10 −5 for Set (P). The second determination is the most stringent limit on the variation of µ over the last 12 Gyr ever obtained. The correlation found using Set (A) seems to show that some amount of systematic error is hidden in the determination of energy levels of the H 2 molecule.