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Item Limits on the time variation of the electromagnetic fine-structure constant in the low energy limit from absorption lines in the spectra of distant quasars(2011-07-06) Srianand, R.; Chand, Hum; Petitjean, Patrick; et al.Most of the successful physical theories rely on the constancy of few fundamental quantities (such as the speed of light, c, the fine-structure constant, α, the proton to electron mass ratio, µ, etc), and constraining the possible time variations of these fundamental quantities is an important step toward a complete physical theory. Time variation of α can be accurately probed using absorption lines seen in the spectra of distant quasars. Here, 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 α derived 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 (z≃1.55) corresponds to a look-back time of 9.7 Gyr in the most favored cosmological model today. This gives a 3σ limit, −2.5 × 10−16 yr −1 ≤ (∆α/α∆t) ≤ +1.2 × 10−16 yr −1, for the time variation of α, that forms the strongest constraint obtained based on high redshift quasar absorption line systems.Item VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems: Physical conditions in the neutral gas(2005-06-01) Srianand, R.; Petitjean, Patrick; Ledoux, C´edric; et al.We study the physical conditions in damped Lyman-α systems (DLAs), using a sample of 33 systems toward 26 QSOs acquired for a recently completed survey of H2 by Ledoux et al. (2003). We use the column densities of H2 in different rotational levels, together with those of C i, C i ∗, C i ∗∗, C ii ∗ and singly ionized atomic species to discuss the kinetic temperature, the density of hydrogen and the electronic density in the gas together with the ambient UV radiation field. Detailed comparisons are made between the observed properties in DLAs, the interstellar medium (ISM) of the Galaxy, the large and small Magellanic clouds (LMC and SMC).The mean kinetic temperature of the gas corresponding to DLA subcomponents in which H2 absorption line is detected, derived from the ortho-to-para ratio (153±78 K), is higher than that measured in the ISM (77±17 K) and the Magellanic clouds (82±21 K). Typical pressure in these components (corresponding to T = 100−300 K and nH = 10−200 cm−3), measured using C i fine-structure excitation, are higher than what is measured along ISM sightlines. This is consistent with the corresponding higher values for N(H2,J=2)/N(H2,J=0) seen in DLAs. From the column densities of the high-J rotational levels, we derive that the typical radiation field in the H2 bearing components is of the order of or slightly higher than the mean UV field in the Galactic ISM. Determination of electron density in the gas with H2 and C i show the ionization rate is similar to that of a cold neutral medium (CNM) in a moderate radiation field. This, together with the fact that we see H2 in 13-20% of the DLAs, can be used to conclude that DLAs at z > 1.9 could contribute as much as 50% star formation rate density seen in Lyman break galaxies (LBGs).C ii ∗ absorption line is detected in all the components where H2 absorption line is seen. The excitation of C ii in these systems is consistent with the physical parameters derived from the excitation of H2 and C i. We detect C ii ∗ in about 50% of the DLAs and therefore in a considerable fraction of DLAs that do not show H2. In part of the later systems, physical conditions could be similar to that in the CNM gas of the Galaxy. However, the absence of C i absorption line and the presence of Al iii absorption lines with a profile similar to the profiles of singly ionized species suggest an appreciable contribution from warm (WNM) and/or partially ionized gas. The absence of H2, for the level of metallicity and dust depletion seen in these systems, are consistent with low densities (i.e nH 6 1 cm−3) for a radiation field similar to the mean Galactic UV field.Item Velocity-metallicity correlation for high-z DLA galaxies: Evidence for a mass-metallicity relation?(2006-06-08) Ledoux, C.; Petitjean, Patrick; Fynbo, J. P. U.; et al.Item Nitrogen and Oxygen abundances in the neutral gas at high redshift(2007-12-17) Petitjean, Patrick; Ledoux, C.; Srianand, R.Aims. We study the Oxygen and Nitrogen abundances in the interstellar medium of high-redshift galaxies. Methods. We use high resolution and high signal-to-noise ratio spectra of Damped Lyman-α (DLA) systems detected along the line-of-sight to quasars to derive robust abundance measurements from unsaturated metal absorption lines. Results. We present results for a sample of 16 high-redshift DLAs and strong sub-DLAs (log N(H i) > 19.5, 2.4 < zabs <3.6) including 13 new measurements. We find that the Oxygen to Iron abundance ratio is pretty much constant with [O/Fe] ∼ +0.32±0.10 for −2.5 < [O/H] < −1.0 with a small scatter around this value. The Oxygen abundance follows quite well the Silicon abundance within ∼0.2 dex although the Silicon abundance could be slightly smaller for [O/H] < −2. The distribution of the [N/O] abundance ratio, measured from components that are detected in both species, is somehow double peaked: five systems have [N/O] > −1 and nine systems have [N/O] < −1.15. In the diagram [N/O] versus [O/H], a loose plateau is possibly present at [N/O] ∼ −0.9 that is below the so-called primary plateau as seen in local metal-poor dwarf galaxies ([N/O] in the range −0.57 to −0.74). No system is seen above this primary plateau whereas the majority of the systems lie well below with a large scatter. All this suggests a picture in which DLAs undergo successive star-bursts. During such an episode, the [N/O] ratio decreases sharply because of the rapid release of Oxygen by massive stars whereas inbetween two bursts, Nitrogen is released by low and intermediate-mass stars with a delay and the [N/O] ratio increases.Item Kinematics and star formation activity in the z=2.03954 damped Lyman-alpha system towards PKS 0458-020(2005-12-01) Heinmuller, Janine; Srianand, R.; Petitjean, Patrick; et al.We present UVES observations of the log N(H ) = 21.7 damped Lyman-α system at zabs = 2.03954 towards the quasar PKS 0458−020. H Lyman-α emission is detected in the center of the damped Lyman-α absorption trough. Metallicities are derived for Mg , Si , P , Cr , Mn , Fe and Zn and are found to be −1.21 ± 0.12, −1.28 ± 0.20, −1.54 ± 0.11, −1.66 ± 0.10, −2.05 ± 0.11, −1.87 ± 0.11, −1.22 ± 0.10, respectively, relative to solar. The depletion factor is therefore of the order of [Zn/Fe] = 0.65. We observe metal absorption lines to be blueshifted compared to the Lyman-α emission up to a maximum of ∼100 and 200 km s−1 for low and high-ionization species respectively. This can be interpreted either as the consequence of rotation in a large (∼7 kpc) disk or as the imprint of a galactic wind. The star formation rate (SFR) derived from the Lyman-α emission, 1.6M⊙yr −1 , is compared with that estimated from the observed C ∗ absorption. No molecular hydrogen is detected in our data, yielding a molecular fraction log f < −6.52. This absence of H2 can be explained as the consequence of a high ambient UV flux which is one order of magnitude larger than the radiation field in the ISM of our Galaxy and originates in the observed emitting region.Item Multiwavelength investigation of a near-solar metallicity sub-DLA at Zabs=1.3647 towards PKS 0237-233(2006-11-10) Srianand, R.; Gupta, Neeraj; Petitjean, PatrickItem Metallicity as a criterion to select H2 bearing damped lyman-alpha systems(2006-07-17) Petitjean, Patrick; Ledoux, C.; Noterdaeme, P.; et al.Item C iv absorption in damped and sub-damped Lyman-alpha systems: Correlations with metallicity and implications for galactic winds at z~2-3(2007-07-27) Fox, Andrew J.; Ledoux, C.; Petitjean, Patrick; et al.We present a study of Civ absorption in a sample of 63 damped Lyman-α (DLA) systems and 11 sub-DLAs in the redshift range 1.75Item Optical identification of XMM sources in the CFHTLS(2009-05-01) Stalin, C. S.; Petitjean, Patrick; Srianand, R.; et al.We summarize the attempts by our group and others to derive constraints on variations of fundamental constants over cosmic time using quasar absorption lines. Most upper limits reside in the range 0.5 1.5 10 5 at the 3 level over a redshift range of approximately 0:5 2:5 for the fine-structure constant, , the proton-to-electron mass ratio, and a combination of the proton gyromagnetic factor and the two previous constants, gp( 2= ) , for only one claimed variation of . It is therefore very important to perform new measurements to improve the sensitivity of the numerous methods to at least <0.1 10 5 which should be possible in the next few years. Future instrumentations on ELTs in the optical and/or ALMA, EVLA and SKA pathfinders in the radio will undoutedly boost this field by allowing to reach much better signal-to-noise ratios at higher spectral resolution and to perform measurements on molecules in the ISM of high redshift galaxiItem Damped and sub-damped Lyman-alpha absorbers in z > 4 QSOs(2009-10-01) Guimaraes, R.; Petitjean, PatrickWe present the results of a survey for damped (DLA, log N(H i) > 20.3) and sub-damped Lyman-α systems (19.5 < log N(H i) < 20.3) at z > 2.55 along the lines-of-sight to 77 quasars with emission redshifts in the range 4 < zem < 6.3. Intermediate resolution (R ∼ 4300) spectra have been obtained with the Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total of 100 systems with log N(H i) > 19.5 are detected of which 40 systems are damped Lyman-α systems for an absorption length of ∆X = 378. About half of the lines of sight of this homogeneous survey have never been investigated for DLAs.We study the evolution with redshift of the cosmological density of the neutral gas and find, consistently with previous studies at similar resolution, that ΩDLA,HI decreases at z > 3.5. The overall cosmological evolution of ΩHI shows a peak around this redshift. The H i column density distribution for log N(H i) ≥ 20.3 is fitted, consistently with previous surveys, with a single power-law of index α ∼ -1.8±0.25. This power-law overpredicts data at the high-end and a second, much steeper, power-law (or a gamma function) is needed. There is a flattening of the function at lower H i column densities with an index of α ∼ −1.4 for the column density range log N(H i) = 19.5−21. The fraction of H i mass in sub-DLAs is of the order of 30%. The H i column density distribution does not evolve strongly from z ∼ 2.5 to z ∼ 4.5.