2006 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/335
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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 On the variation of the fine-structure constant : Very high resolution spectrum of QSO HE 0515-4414(2006-01-10) Chand, Hum; Srianand, R.; Petitjean, Patrick; et al.We present a detailed analysis of a very high resolution (R ≈ 112, 000) spectrum of the quasar HE 0515−4414 obtained using the High Accuracy Radial velocity Planet Searcher (HARPS) mounted on the ESO 3.6 m telescope at the La Silla observatory. The main aim is to use HARPS spectrum of very high wavelength calibration accuracy (better than 1 mÅ), to constrain the variation of α = e² /~c and investigate any possible systematic inaccuracies in the wavelength calibration of the UV Echelle Spectrograph (UVES) mounted on the ESO Very Large Telescope (VLT). Methods. A cross-correlation analysis between the Th-Ar lamp spectra obtained with HARPS and UVES is carried out to detect any possible shift between the two spectra. Absolute wavelength calibration accuracies, and how that translate to the uncertainties in ∆ α/α are computed using Gaussian fits for both lamp spectra. The value of ∆α/α at Zabs = 1.1508 is obtained using Many Multiplet method, and simultaneous Voigt profile fits of HARPS and UVES spectra. Results. We find the shift between the HARPS and UVES spectra has mean around zero with a dispersion of σ ≃ 1 mÅ. This is shown to be well within the wavelength calibration accuracy of UVES (i.e σ ≃ 4 mÅ). We show that the uncertainties in the wavelength calibration induce an error of about, ∆α/α ≤ 10−⁶ , in the determination of the variation of the fine-structure constant. Thus, the results of non-evolving ∆α/α reported in the literature based on UVES/VLT data should not be heavily influenced by problems related to wavelength calibration uncertainties. Our higher resolution spectrum of the zabs = 1.1508 Damped Lyman-α system toward HE 0515−4414 reveals more components compared to the UVES spectrum. Using only Fe II lines of zabs = 1.1508 system, we obtain ∆α/α = (0.05 ± 0.24) × 10−⁵ . This result is consistent with the earlier measurement for this system using the UVES spectrum alone.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 Molecular hydrogen in a damped lyman-alpha system at Zabs = 4.224(2006-02-09) Ledoux, C.; Petitjean, Patrick; Srianand, R.We present the direct detection of molecular hydrogen at the highest redshift known today (zabs = 4.224) in a Damped Lyman-α (DLA) system toward the quasar PSS J 1443+2724. This absorber is remarkable for having one of the highest metallicities amongst DLA systems at zabs > 3, with a measured iron abundance relative to Solar of −1.12 ± 0.10. We provide for the first time in this system accurate measurements of Ni, Mg ii, S ii and Ar i column densities. The sulfur and nitrogen abundances relative to Solar, −0.63 ± 0.10 and −1.38 ± 0.10 respectively, correspond exactly to the primary nitrogen production plateau. H2 absorption lines are detected in four different rotational levels (J = 0, 1, 2 and 3) of the vibrational ground-state in three velocity components with total column densities of logN(H2) = 17.67, 17.97, 17.48 and 17.26 respectively. The J = 4 level is tentatively detected in the strongest component with logN(H2) ∼ 14. The mean molecular fraction is log f = −2.38 ± 0.13, with f = 2N(H2)/(2N(H2) + N(Hi)). We also measure logN(HD)/N(H2) < −4.2. The excitation temperatures T01 for the two main components of the system are 96 and 136 K respectively. We argue that the absorbing galaxy, whose star formation activity must have started at least 2− 5× 108 yrs before z = 4.224, is in a quiescent state at the time of observation. The density of the gas is small, nH ≤ 50 cm−3 , and the temperature is of the order of T ∼ 90 − 180 K. The high excitation of neutral carbon in one of the components can be explained if the temperature of the Cosmic Microwave Background Radiation has the valueexpected at the absorber redshift, T = 14.2 K. These observations demonstrate the feasibility to study H2 at the highest redshifts provided high enough spectral resolution and good S/N ratio are achieved.Item Metallicity as a criterion to select H2 bearing damped lyman-alpha systems(2006-07-17) Petitjean, Patrick; Ledoux, C.; Noterdaeme, P.; et al.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.