R Srianand

Learn 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)
It has been realised in the last few years that strong constraints on the time-variations of dimensionless fundamental constants of physics can be derived at any redshift from QSO absorption line systems. Variations of the fine structure constant, α, the proton-to-electron mass ratio, μ, or the combination, x = α 2 gp /μ, where gp is the proton gyromagnetic(More)
We present the detection of carbon monoxide molecules (CO) at z = 1.6408 towards the quasar SDSS J160457.50+220300.5 using the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph. CO absorption is detected in at least two components in the first six AX bands and one d-X(5-0) inter-band system. This is the second detection of this kind along a(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 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)