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Item Physical conditions in the neutral interstellar medium at z=2.43 toward Q2348-011(2007-03-29) Noterdaeme, P.; Srianand, R.; Petitjean, Patrick; et al.Aims. We aim at deriving the physical conditions in the neutral gas associated with damped Lyman-α systems using observation and analysis of H2 and C absorptions. Methods. We obtained a high-resolution VLT-UVES spectrum of the quasar Q2348−011 over a wavelength range that covers most of the prominent metal and molecular absorption lines from the log N(H ) = 20.50±0.10 damped Lyman-α system at zabs = 2.4263. We detected H2 in this system and measured column densities of H2, C , C ∗, C∗∗ , Si , P , S , Fe , and Ni . From the column density ratios and, in particular, the relative populations of H2 rotational and C fine-structure levels, we derived the physical conditions in the gas (relative abundances, dust-depletion, particle density, kinetic temperature, and ionising flux) and discuss physical conditions in the neutral phase. Results. Molecular hydrogen was detected in seven components in the first four rotational levels (J = 0-3) of the vibrational ground state. Absorption lines of H2 J = 4 (resp. J = 5) rotational levels are detected in six (resp. two) of these components. This leads to a total molecular fraction of log f ≃ −1.69+0.37 −0.58. Fourteen components are needed to reproduce the metal-line profiles. The overall metallicity is found to be −0.80, −0.62, −1.17±0.10 for, respectively, [Si/H], [S/H] and [Fe/H]. We confirm the earlier findings that there is a correlation between log N(Fe )/N(S ) and log N(Si )/N(S ) from different components indicative of a dust-depletion pattern. Surprisingly, however, the depletion of metals onto dust in the H2 components is not large in this system: [Fe/S] = −0.8 to −0.1. The gas in H2-bearing components is found to be cold but still hotter than similar gas in our Galaxy (T > 130 K, instead of typically 80 K) and dense (n ∼ 100 − 200 cm−3 ). There is an anti-correlation (R = −0.97) between the logarithm of the photo-absorption rate, log β0, and log N(H2)/N(C ) derived for each H2 component. We show that this is mostly due to shielding effects and imply that the photo-absorption rate β0 is a good indicator of the physical conditions in the gas. We find that the gas is immersed in an intense UV field, about one order of magnitude higher than in the solar vicinity. These results suggest that the gas in H2-bearing DLAs is clumpy, and star-formation occurs in the associated objectItem Diffuse molecular gas at high redshift: Detection of CO molecules and the 2175 A* dust feature at z=1.64(2009-06-01) Noterdaeme, P.; Ledoux, C.; Srianand, R.; et al.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 A-X bands and one d-X(5-0) inter-band system. This is the second detection of this kind along a quasar line of sight. The CO absorption profiles are well modelled assuming a rotational excitation of CO in the range 6 < Tex < 16 K, which is consistent with or higher than the temperature of the Cosmic Microwave Background Radiation at this redshift. We derive a total CO column density of N(CO) = 4 × 1014 cm−2 . The measured column densities of S i, Mg i, Zn ii, Fe ii and Si ii indicate a dust depletion pattern typical of cold gas in the Galactic disc. The background quasar spectrum is significantly reddened (u−K ∼ 4.5 mag) and presents a pronounced 2175 Å dust absorption feature at the redshift of the CO absorber. Using a control sample of ∼500 quasars we find the chance probability for this feature to be spurious is ∼0.3%. We show that the spectral energy distribution (SED) of the quasar is well fitted with a QSO composite spectrum reddened with a Large Magellanic Cloud supershell extinction law at the redshift of the absorber. It is noticeable that this quasar is absent from the colour-selected SDSS quasar sample. This demonstrates our current view of the Universe may be biased against dusty sightlines. These direct observations of carbonaceous molecules and dust open up the possibility of studying physical coItem Diffuse molecular gas at high redshift: Detection of CO molecules and the 2175 A* dust feature at z=1.64(2009-06-01) Noterdaeme, P.; Ledoux, C.; Srianand, R.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 A-X bands and one d-X(5-0) inter-band system. This is the second detection of this kind along a quasar line of sight. The CO absorption profiles are well modelled assuming a rotational excitation of CO in the range 6 < Tex < 16 K, which is consistent with or higher than the temperature of the Cosmic Microwave Background Radiation at this redshift. We derive a total CO column density of N(CO) = 4 × 1014 cm−2 . The measured column densities of S i, Mg i, Zn ii, Fe ii and Si ii indicate a dust depletion pattern typical of cold gas in the Galactic disc. The background quasar spectrum is significantly reddened (u−K ∼ 4.5 mag) and presents a pronounced 2175 Å dust absorption feature at the redshift of the CO absorber. Using a control sample of ∼500 quasars we find the chance probability for this feature to be spurious is ∼0.3%. We show that the spectral energy distribution (SED) of the quasar is well fitted with a QSO composite spectrum reddened with a Large Magellanic Cloud supershell extinction law at the redshift of the absorber. It is noticeable that this quasar is absent from the colour-selected SDSS quasar sample. This demonstrates our current view of the Universe may be biased against dusty sightlines. These direct observations of carbonaceous molecules and dust open up the possibility of studying physical conditions and chemistry of diffuse molecular gas in high redshift galaxies.