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Item The Z abs~Z em absorption line systems toward QSO J2233-606 in the hubble deep field south: Ne VIIIλλ770,780 absorption and partial coverage(2015-03-01) Petitjean, Patrick; Srianand, R.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 Detecting cold gas at intermediate redshifts: GMRT survey using MgII systems(2006-11-28) Gupta, Neeraj; Srianand, R.; Petitjean, Patrick; et al.Intervening H i 21-cm absorption systems at z ≥ 1.0 are very rare and only 4 confirmed detections have been reported in the literature. Despite their scarcity, they provide interesting and unique insights into the physical conditions in the interstellar medium of high-z galaxies. Moreover, they can provide independent constraints on the variation of fundamental constants. We report 3 new detections based on our ongoing Giant Metrewave Radio Telescope (GMRT) survey for 21-cm absorbers at 1.10 ≤ zabs ≤ 1.45 from candidate damped Lyman-α systems. The 21-cm lines are narrow for the zabs= 1.3710 system towards SDSS J0108−0037 and zabs= 1.1726 system toward SDSS J2358−1020. Based on line full-width at half maximum, the kinetic temperatures are ≤ 5200 K and ≤ 800 K, respectively. The 21-cm absorption profile of the third system, zabs=1.1908 system towards SDSS J0804+3012, is shallow, broad and complex, extending up to 100 km s−ᶥ . The centroids of the 21-cm lines are found to be shifted with respect to the corresponding centroids of the metal lines derived from SDSS spectra. This may mean that the 21-cm absorption is not associated with the strongest metal line component.Item Uncovering strong MgII absorbing galaxies: Imaging below the Lyman limit(2009-08-01) Christensen, L.; Petitjean, Patrick; Ledoux, C.Context. The nature of the galaxies that give rise to absorption lines, such as damped Lyman-α systems (DLAs) or strong Mg ii lines, in quasar spectra is difficult to investigate in emission. These galaxies can be very faint and located close to the lines of sight of the much brighter background quasars. Aims. Taking advantage of the total absorption of the QSO light bluewards of the Lyman limit of two DLAs at z > 3.4, we look for the continuum emission from intervening galaxies at z ≈ 2 that are identified via strong metal absorption lines. The Mg ii absorbers have equivalent width large enough to be potential DLA systems. Methods. Deep images are obtained with the FOcal Reducer and Spectrograph (FORS1) on the Very Large Telescope for the fields towards SDSS J110855+120953 and SDSS J140850+020522. These quasars have Mg ii absorption lines at z = 1.87 (Wr(Mg ii) = 2.46 Å) and z = 1.98 (Wr(Mg ii) = 1.89 Å), respectively, and each QSO has two intervening higher redshift DLAs at z > 3. The U and R bands of FORS1 lie blue and redwards of the Lyman limit of the background DLAs, allowing us to search for emission from the foreground galaxies directly along the lines of sight to the QSOs. Results. No galaxies are found close to the sight line of the QSO to a point source limit of UAB ∼ 28.0. In both fields, the closest objects lie at an impact parameter of ∼5′′ corresponding to ∼40 kpc in projection at z = 2, and have typical colours of star forming galaxies at that redshift. However, the currently available data do not allow us to confirm if the galaxies lie at the same redshifts as the absorption systems. A more extended structure is visible in the SDSS J14085+020522 field at an impact parameter of 0. ′′ 8 or 7 kpc. If these objects are at z ≈ 2 their luminosities are 0.03–0.04 L∗ in both fields. The star formation rates estimated from the UV flux are 0.5–0.6 M⊙ yr −1 , while the SFRs are half these values if the U band flux is due to Lyα emission alone. Conclusions. The non-detection of galaxies near to the line of sight is most likely explained by low metallicities and luminosities of the Mg ii galaxies. Alternatively, the Mg ii clouds are part of extended halos or in outflows from low-metallicity galaxies.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 1.75