Raghunathan Srianand

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We present the results of a detailed many-multiplet analysis performed on a new sample of Mg ii systems observed in high quality quasar spectra obtained using the Very Large Telescope. The weighted mean value of the variation in alpha derived from our analysis over the redshift range 0.4</=z</=2.3 is Deltaalpha/alpha=(-0.06+/-0.06)x10(-5). The median(More)
We present the results of a search for damped Lyman-α (DLA) systems in the Sloan Digital Sky Survey II (SDSS), Data Release 7. We use a fully automatic procedure to identify DLAs and derive their column densities. The procedure is checked against the results of previous searches for DLAs in SDSS. We discuss the agreements and differences and show the(More)
A new constraint on the time dependence of the proton−to−electron mass ratio Abstract. A new limit on the possible cosmological variation of the proton-to-electron mass ratio µ = mp/me is estimated by measuring wavelengths of H2 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(More)
We present the direct detection of molecular hydrogen at the highest red-shift known today (z abs = 4.224) in a Damped Lyman-α (DLA) system toward the quasar PSS J 1443+2724. This absorber is remarkable for having one of the highest metallicities amongst DLA systems at z abs > 3, with a measured iron abundance relative to Solar of −1.12 ± 0.10. We provide(More)
We used our database of VLT-UVES quasar spectra to build up a sample of 70 Damped Lyman-α (DLA) or strong sub-DLA systems with total neutral hydrogen column densities of log N(H ) > ∼ 20 and redshifts in the range 1.7 < z abs < 4.3. For each of the systems, we measured in an homogeneous manner the metallicities relative to Solar, [X/H] (with X = Zn, or S(More)
While gravitationally lensed quasars are expected to display an odd number of images, invariably systems are observed with an even number of quasars. For this, lensing galaxies must have very small core radii; this provides strong demagnification of one of the images. High resolution imaging of the gravitationally lensed BAL quasar, APM08279+5255, reveals(More)
We present the first detection of carbon monoxide (CO) in a damped Lyman-α system (DLA) at z abs =2.41837 toward SDSS J143912.04+111740.5. We also detected H2 and HD molecules. The measured total column densities (in log units) of H i, H2, and CO are 20. respectively, indicating a high metal enrichment and a depletion pattern onto dust-grains similar to the(More)
Aims. We aim at deriving the physical conditions in the neutral gas associated with damped Lyman-α systems using observation and analysis of H 2 and C i absorptions. Methods. We obtained a high-resolution VLT-UVES spectrum of the quasar Q 2348−011 over a wavelength range that covers most of the prominent metal and molecular absorption lines from the log N(H(More)
Aims. We probe the physical conditions in high-redshift damped Lyman-α systems (DLAs) using the observed molecular fraction and the rotational excitation of molecular hydrogen. Methods. We search for Lyman-and Werner-band absorption lines of molecular hydrogen in the VLT/UVES spectra of background QSOs at the redshift of known DLAs. Results. We report two(More)
We investigated abundance ratios along the profiles of six high-redshift Damped Lyman-α systems, three of them associated with H2 absorption, and derived optical depths in each velocity pixel. The variations of the pixel abundance ratios were found to be remarkably small and usually smaller than a factor of two within a profile. This result holds even when(More)