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Item New measurement of sinc metallicity in a DLA at z ~ 3.35(2002-03-02) Peroux, C.; Petitjean, Patrick; Aracil, BastienWe present chemical abundance measurements in the zabs = 3.35045 Damped Lyman-α (DLA) system observed in the UVES spectrum of the BAL quasar BR 1117−1329. We measure a neutral hydrogen column density N(HI) = 6.9±1.7×1020 atoms cm−2 and derive mean abundances relative to solar: [Si/H] = −1.26 ± 0.13, [Fe/H] = −1.51±0.13, [Ni/H] = −1.57±0.13, [Cr/H] = −1.36±0.13, [Zn/H] = −1.18±0.13, [Al/H] > −1.25, [O/H] > −1.25 and [N/H] < −2.24. This is the third measurement of Zn, an element mildly depleted onto dust grain, at zabs > 3. The iron to zinc and chromium to zinc ratios, [Fe/Zn] = −0.33 ± 0.05 and [Cr/Zn] = −0.18 ± 0.05 demonstrate that the absorber has a low dust content. The nitrogen ratio [N/Si] < −0.98 suggests that the “secondary” N production process is taking place in this DLA. Finally, this absorber does not seem to present a convincing α- enhancement as shown by the α over Fe-peak element ratios: [Si/Fe] = 0.25±0.06, [Si/Cr] = 0.10 ± 0.06 and [Si/Zn] = −0.08 ± 0.06.Item Molecular hydrogen at Zabx=1.973 towards Q0013 - 004: Dust depletion pattern in damped Lyman - alpha systems(2002-03-06) Petitjean, Patrick; Srianand, R.; Ledoux, C.We study the dust depletion pattern in different well separated components of the Zabs = 1.973, log N(H I) = 20.83, damped Lyman-a system toward Q 0013-004. The apparent correlation between [Fe/S] and [Si/S] in the components indicates that the abundance pattern is indeed due to dust-depletion. In particular, we find evidence for depletion similar to what is observed in cold gas of the Galactic disk in one of the weakest components ([Fe/Zn] = -1.62, [Fe/S]= -1.82, [Zn/S] = -0.2, [Si/S]= -0.92) in which molecular hydrogen is detected with log N(H2) '" 16.5. This is the first time that such depletion is seen in a DLA system. Extinction due to this component is negligible owing to small total HI column density, log N(HI ) ::;;19.4.This observation supports the possibility that current samples of DLA systems might be biased against the presence of cold and dusty gas along the line of sight. The global metallicities of this peculiar DLA system in which 0 I and C II are spread over ",1050 km S-1 are [P/H] = -0.64, [Zn/H] = -0.75 and [S/H] = -0.76 relative to solar. The overall molecular fraction is in the range -2.7 < log f < -0.6. which is the highest value found for DLA systems. H2 is detected in four components at -625, -475, 0 and 80 km S-1 relative to the strongest component at Zabs = 1.97296.CO is not detected (log N(CO)/ N(H r) < -8) and HD could be present at Zabs = 1.97380. We show that the presence of H2 is closely related to the physical conditions in the gas: high particle density together with low temperature. Excitation of high J levels and molecular fraction vary largely from one component to the ot.her suggesting that the UV radiation field is highly inhomogeneous through the system. Gas pressure, estimated from C I absorptions, is larger than what is observed in the ISM of our Galaxy. This, together with the complex kinematics, suggests that part of the gas is subject to high compression due to either collapse, merging and/or supernovae explosion. This is probably a consequence of star-formation activity in the vicinity of the absorbing gasItem Structure of the Mg II and damped Lyman- systems along the line of sight to APM 08279+5255(2000-05-24) Petitjean, Patrick; Aracil, Bastien; Srianand, R.; et al.A study of the absorption systems toward the gravitationally lensed quasar APM 08279+5255 is pre-sented.Most of the Mg ii systems in the redshift range z ∼ 1.2– 2.07, although saturated, show large residuals at the bot- tom of the lines. The most likely interpretation is that individual clouds within Mg ii halos do cover only one of the two brightest QSO images. The separation between the two lines of sight decreases from 1.7 to 0.7 h−1 75 kpc (qo = 0.5, zlens = 1) between z = 1.22 and z = 2.07. This reveals that Mg ii halos are made of a collection of clouds of radius smaller than about 1 h−1 75 kpc. Two strong Mg ii absorbers at zabs = 1.062 and 1.181 are studied in detail. This is the first time that the Na iλ3303 doublet is detected in such high redshift systems. To- gether with the detection of the Mg iλ2852 transition, this strongly constrains the physical characteristics of the gas. The N(Na i)/N(Mg i) ratio is found to be larger than unity, implying that the gas is cool and neutral. The Doppler parameters measured in individual and well de- tached components is probably as small as 1 km s−1. The column densities of Na i, Ca ii, Mg i, Ti ii, Mn ii and Fe ii observed at zabs = 1.1801 are very close to that observed along the line of sight towards 23 Ori in our Galaxy. The shape of the QSO continuum is consistent with attenu- ation by dust at z ∼ 1 (AV ∼ 0.5 mag). Altogether it is found that the H i column density at z = 1 is of the order of 1 to 5 1021 cm−2, the corresponding metallicity is in the range 1–0.3 Z⊙, the overall dust-to-metal ratio is about half that in our Galaxy and the relative deple- tion of iron, titanium, manganese and calcium is similar to what is observed in cool gas in the disk of our Galaxy. The objects associated with these two systems could both con-tribute to the lens together with another possible strong system at zabs = 1.1727 and the strong Lyman-α system at zabs = 2.974. The probable damped Lyman-α system at zabs = 2.974 has 19.8 < log N(H i) < 20.3. The transverse dimension of the absorber is larger than 200 h−1 75 pc. Column densities of Al ii, Fe ii, Si ii, C ii and O i indicate abundances rela- tive to solar of −2.31, −2.26, −2.10, −2.35 and −2.37 for, respectively, Fe, Al, Si, C and O (for log N(H i) = 20.3). These surprizingly similar values indicate that the amount of dust in the cloud is very small as are any deviations from relative solar abundances. It seems likely that the upper limits found for the zinc metallicity of several damped Lyman-α systems at z > 3 in previous surveys is indica- tive of a true cosmological evolution of the metallicity in individual systems.Item Detection of molecular hydrogen in a near solar-metallicity damped Lyman - alpha system at Zabc ~ 2 toward Q 0551 - 366 Authors: Ledoux, C.(2002-05-01) Ledoux, C.; Srianand, R.; Petitjean, PatrickWe report the detection of H2, C I, C 1*, C I ** and Cl I lines in a near Solar-metallicity ([Zn/H] = -0.13) damped Lyman-a (DLA) system at Zabs = 1.962 observed on the line of sight to the quasar Q 0551-366. The iron-peak elements, X = Fe, Cr and Mn are depleted compared to zinc, [X/Zn] "'" -0.8, probably because they are tied up onto dust grains. Among the three detected Hs-bearing clouds, spanning 55 km S-l in velocity space, we derive a total molecular hydrogen column density N(H2) = 2.6 X 1017 cm- 2 and a mean molecular fraction f = 2N(H2)/(2N(H2) + N(H I» = 1.7 x 10- 3. The depletion of heavy elements (S, Si, Mg, Mn, Cr, Fe, Ni and Ti) in the central component is similar to that observed in the diffuse neutral gas of the Galactic halo. This depletion is approximately the same in the six C I-detected components independently of the presence or absence of H2. The gas clouds in which H2 is detected always have large densities, nH > 30 cm- 3 , and low temperatures, T01 ~ 100 K. This shows that presence of dust, high particle density and/or low temperature are required for molecules to be present. The photo-dissociation rate derived in the components where H2 is detected suggests the existence of a local UV radiation field similar in strength to the one in the Galaxy. Star formation therefore probably occurs near these H2-bearing clouds.Item Collimated flow driven by radiative pressure from the nucleus of quasar Q 1511 + 091(2011-07-06) Srianand, R.; Petitjean, Patrick; Ledoux, C.; et al.High velocity outflows from quasars are revealed by the absorption signatures they produce in the spectrum of the quasar. Clues on the nature and origin of these flows are important for our understanding of the dynamics of gas in the central regions of the Active Galactic Nucleus (AGNs) but also of the metal enrichment of the intergalactic space. Line radiation pressure has often been suggested to be an important process in driving these outflows, however no convincing evidence has been given so far. Here we report observation of a highly structured flow, toward Q 1511+091, where the velocity separations between distinct components are similar to O vi, N v and C iv doublet splittings with some of the profiles matching perfectly. This strongly favors the idea that the absorbing clumps originate at similar physical location and are driven by radiative acceleration due to resonance lines. The complex absorption can be understood if the flow is highly collimated so that the different optically thick clouds are aligned and cover the same region of the background source. One component shows saturated H i Lyman series lines together with absorptions from excited levels from C ii and Si ii but covers only 40% of the source of continuum. The fact that clouds cover only part of the small continuum source implies that the flow is located very close to it.Item Outflowing material in the Zem=4.92 BAL QSO SDSS J160501.21 - 011220.0(2011-07-05) Gupta, Neeraj; Srianand, R.; Petitjean, Patrick; et al.We present the analysis of broad absorption lines (BALs) seen in the spectrum of the zem ≃4.92 QSO SDSS J160501.21-011220.0. Our high spectral resolution UVES spectrum shows two well detached absorption line systems at zabs= 4.685 and 4.855. The system at zabs= 4.855 covers the background source completely suggesting that the gas is located outside the broad emission line region. On the contrary the system at zabs= 4.685, which covers only on the continuum source, has a covering factor of the order of 0.9. Physical conditions are investigated in the BAL system at zabs= 4.855 using detailed photoionization models. The observed H i absorption line together with the limits on C ii and Si ii absorptions suggest that 16 < log N(H i) (cm−2 ) < 17 in this system. Comparison with models show that the observed column densities of N v , Si iv and C iv in this system require that nitrogen is underabundant by more than a factor 3 compared to silicon if the ionizing radiation is similar to a typical QSO spectrum. This is contrary to what is usually derived for the emission line gas in QSOs. We show that the relative suppression in the N v column density can be explained for Solar abundance ratios or abundance ratios typical of Starburst abundances if an ionizing spectrum devoid of X-rays is used instead. Thus, if the composition of BAL is like that of the emission line regions it is most likely that the cloud sees a spectrum devoid of X-rays similar to what we observe from this QSO. This is consistent with the fact that none of our models have high Compton optical depth to remove X-rays from the QSO. Similar arguments lead to the conclusion that the system at zabs= 4.685 as well is not Compton thick. Using simple Eddington arguments we show that the mass of the central black hole is ∼ 8 × 108 M⊙. This suggests that the accretion onto a seed black hole must have started as early as z = 11.Item Probing the time-variation of the fine-structure constant: Results based on Si IV doublets from a UVES sample(2011-07-06) Chand, Hum; Petitjean, Patrick; Srianand, R.; et al.We report a new constraint on the variation of the fine-structure constant based on the analysis of 15 Si iv doublets selected from a ESO-UVES sample. We find ∆α/α = (+0.15 ± 0.43) × 10−5 over a redshift range of 1.59 ≤ z ≤ 2.92 which is consistent with no variation in α. This result represents a factor of three improvement on the constraint on ∆α/α based on Si iv doublets compared to the published results in the literature. The alkali doublet method used here avoids the implicit assumptions used in the many-multiplet method that chemical and ionization inhomogeneities are negligible and isotopic abundances are close to the terrestrial value.Item Probing the cosmological variation of the fine-structure constant:Results on VLT-UVES sample(2011-07-06) Chand, Hum; Srianand, R.; Petitjean, Patrick; et al.Abstract. Development of fundamental physics relies on the constancy of various fundamental quantities such as the fine structure 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 many-multiplet analysis, to detect the possible variation of fine-structure constant, performed using high signal-to-noise ratio, (∼70 per pixel), high spectral resolution (R ≥45000) observations of 23 Mg ii 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 detail analysis of simulated data set. The spectra of Mg ii doublets and Fe ii multiplets are generated considering variations in α and specifications identical to that of our UVES spectra. We show 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 the systems with very weak lines. Thus we avoided heavily blended systems and the systems with Fe ii column density < 2×1012 cm−2 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 till date.