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Item Molecules in the Zabc = 2.8112 damped system toward PKS 0528-250(2015-03-11) Srianand, R.; Petitjean, PatrickItem 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 Near-solar metallicity damped lyman-alpha system toward the BAL quasar Tol 1037 - 2703(2001-02-01) Srianand, R.; Petitjean, PatrickWe report the detection of a Broad Absorption Line (BAL) outflow in the spectrum of the zem (Mg ii) = 2.201 QSO Tol 1037−2703 with three main BALs at 36000, 25300 and 22300 km s −1 outflow velocities. Although the overall flow is dominated by high ionization lines like N v and C iv , the gas of highest velocity shows absorption from Mg i, Mg ii and Fe ii. Covering factor arguments suggest that the absorbing complexes are physically associated with the QSO and have transverse dimensions smaller than that of the UV continuum emitting region (r < 0.1 pc). We show that the C iv absorption at zabs = 2.082 has a covering factor fc ∼ 0.86 and the absorption profile has varied over the last four years. The detection of absorption from excited fine structure levels of C ii and Si ii in narrow components embedded in the C iv trough reveals large density inhomogeneities. IR pumping is the most likely excitation process. The zabs = 2.139 system is a moderately damped Lyman-α system with log N(H i) ∼ 19.7. The weakness of the metal lines together with the high quality of the data make the metallicity measurements particularly reliable. The absolute metallicity is close to solar with [Zn/H] = −0.26. The α-chain elements have metallicities consistently solar (respectively +0.05, −0.02, −0.03 and −0.15 for [Mg/H], [Si/H], [P/H] and [S/H]) and iron peak elements are depleted by a factor of about two ([Fe/Zn], [Cr/Zn], [Mn/Zn] and [Ni/Zn] are equal to −0.39, −0.27, −0.49, −0.30). Lines from C i are detected but H2 is absent with a molecular to neutral hydrogen fraction less than 8×10−6 . From the ionization state of the gas, we argue that the system is situated ∼few Mpc away from the QSO. High metallicity and low nitrogen abundance, [N/Zn] = −1.40, favor the idea that metals have been released by massive stars during a starburst of less than 0.5 Gyr of age. Using the upper limit on the C i ∗ column density in two components, we obtain upper limits on the background temperature of 16.2 and 13.2 K respectively.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 Physical conditions in broad and associated narrow absorption-line systems toward APM 08279+5255(2000-03-21) Srianand, R.; Petitjean, PatrickResults of a careful analysis of the absorption systems with zabs≃zem seen toward the bright, zem ∼3.91, gravitationally lensed quasar APM 08279+5255 are pre- sented. Two of the narrow-line systems, at zabs = 3.8931 and zabs = 3.9135, show absorptions from singly ionized species with weak or no N v and O vi absorptions at the same redshift. Absorption due to fine structure transitions of C ii and Si ii (excitation energies cor- responding to, respectively, 156µm and 34µm) are de- tected at zabs = 3.8931. Excitation by IR radiation is favored as the column density ratios are consistent with the shape of APM 08279+5255 IR spectrum. The low- ionization state of the system favors a picture where the cloud is closer to the IR source than to the UV source, supporting the idea that the extension of the IR source is larger than ∼200 pc. The absence of fine structure lines at zabs = 3.9135 suggests that the gas responsible for this system is farther away from the IR source. Abundances are ∼0.01 and 1 Z⊙ at zabs = 3.913 and 3.8931 and alu- minum could be over-abundant with respect to silicon and carbon by at least a factor of two and five. All this sug- gests that whereas the zabs= 3.8931 system is probably located within 200 pc from the QSO and ejected at a ve- locity larger than 1000 km s−1, the zabs= 3.9135 system is farther away and part of the host-galaxy. Several narrow-line systems have strong absorption lines due to C iv, O vi and N v and very low neutral hy- drogen optical depths. This probably implies metallicities Z ≥ Z⊙ although firm conclusion cannot be drawn as the exact value depends strongly on the shape of the ionizing spectrum. The C iv broad absorption has a complex structure with mini-BALs (width ≤ 1000 km s−1) and narrow compo-nents superposed on a continuous absorption of smaller optical depth. The continuous absorption is much stronger in O vi indicating that the corresponding gas-component is of higher ionization than the other components in the flow and that absorption structures in the BAL-flow are mainly due to density inhomogeneities. There is a ten- dency for mini-BALs to have different covering factors for different species. It is shown that a few of the absorbing clouds do not cover all the three QSO images, especially we conclude that the zabs = 3.712 system covers only im- age C. Finally we identify narrow components within the BAL- flow with velocity separations within 5 km s−1 of the O vi, N v and Si iv doublet splittings suggesting that line driven radiative acceleration is an important process to explain the out-flow.Item H2 molecules and the nature of damped Lyman-alpha systems(2000-12-14) Petitjean, Patrick; Srianand, R.; Ledoux, C.We report results from our mini-survey for molecular hydrogen in eight high-redshift damped Lyman- α (DLA) systems using the ESO Ultra-violet and Visible Spectrograph on the VLT. In addition, we investigate two systems using ESO public data. We include in the sam- ple the only system where H2 was previously detected and studied at high-spectral resolution. Altogether our sample consists of eleven absorbers with 1.85 < zabs < 3.4. We confirm the presence of H2 in the zabs = 2.3377, metal-poor ([Si/H] = −1.20), system toward PKS 1232+082. The derived molecular fraction, f = 2N(H2)/(2N(H2)+N(H i)) = 4×10−4, is two orders of magnitude less than what has been claimed previ- ously from low-resolution data. The physical conditions within the cloud can be constrained directly from ob- servation. The kinetic temperature and particle density are in the ranges, respectively, 100 < T < 300 K and 30 < nH < 50 cm−3. In addition, UV pumping is of the same order of magnitude than in our Galaxy. The upper limits on the molecular fraction derived in nine of the systems are in the range 1.2×10−7−1.6×10−5. There is no evidence in this sample for any correlation be- tween H2 abundance and relative heavy element depletion into dust grains. This should be investigated using a larger sample however. The molecular abundance in a few DLA systems (and in particular in the two systems where H2 is detected) is consistent with what is seen in the Magel- lanic clouds. But most of the DLA measurements are well below these values. This is probably partly due to small amounts of dust and/or high UV flux. We argue however that the lack of molecules is a direct consequence of high kinetic temperature (T > 3000 K) implying a low forma- tion rate of H2 onto dust grains. Therefore, most of the DLA systems arise in warm and diffuse neutral gas.Item Cosmic microwave background temperature at a redshift of 2.33771(2000-12-18) Srianand, R.; Petitjean, Patrick; Ledoux, C.The Cosmic Microwave Background radiation is a fundamental prediction of Hot Big Bang cosmology. The temperature of its black-body spectrum has been measured at the present time, TCMBR,0 = 2.726±0.010 K, and is predicted to have been higher in the past. At earlier time, the temperature can be measured, in principle, using the excitation of atomic fine structure levels by the radiation field. All previous measurements however give only upper limits as they assume that no other significant source of excitation is present. Here we report the detection of absorption from the first and second fine-structure levels of neutral carbon atoms in an isolated remote cloud at a redshift of 2.33771. In addition, the unusual detection of molecular hydrogen in several rotational levels and the presence of ionized carbon in its excited fine structure level make the absorption system unique to constrain, directly from observation, the different excitation processes at play. It is shown for the first time that the cosmic radiation was warmer in the past. We find 6.0 < TCMBR < 14 K at z = 2.33771 when 9.1 K is expected in the Hot Big Bang cosmology.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.