2009 (IPP)

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Author: search.filters.author.Petitjean, PatrickSubject: search.filters.subject.Galaxies

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    Damped and sub-damped Lyman-alpha absorbers in z > 4 QSOs
    (2009-10-01) Guimaraes, R.; Petitjean, Patrick
    We present the results of a survey for damped (DLA, log N(H i) > 20.3) and sub-damped Lyman-α systems (19.5 < log N(H i) < 20.3) at z > 2.55 along the lines-of-sight to 77 quasars with emission redshifts in the range 4 < zem < 6.3. Intermediate resolution (R ∼ 4300) spectra have been obtained with the Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total of 100 systems with log N(H i) > 19.5 are detected of which 40 systems are damped Lyman-α systems for an absorption length of ∆X = 378. About half of the lines of sight of this homogeneous survey have never been investigated for DLAs.We study the evolution with redshift of the cosmological density of the neutral gas and find, consistently with previous studies at similar resolution, that ΩDLA,HI decreases at z > 3.5. The overall cosmological evolution of ΩHI shows a peak around this redshift. The H i column density distribution for log N(H i) ≥ 20.3 is fitted, consistently with previous surveys, with a single power-law of index α ∼ -1.8±0.25. This power-law overpredicts data at the high-end and a second, much steeper, power-law (or a gamma function) is needed. There is a flattening of the function at lower H i column densities with an index of α ∼ −1.4 for the column density range log N(H i) = 19.5−21. The fraction of H i mass in sub-DLAs is of the order of 30%. The H i column density distribution does not evolve strongly from z ∼ 2.5 to z ∼ 4.5.
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    Constraining fundamental constants of physics with quasar absorption line systems
    (2009-08-01) Petitjean, Patrick; Vivek, M.; Mohan, V.; et al.
    We report long-slit spectroscopic observations of SDSS J092712+294344 carried-out at the recently commissioned 2m telescope in IUCAA Girawali Observatory, India. This AGN-like source is known to feature three sets of emission lines at zem = 0.6972, 0.7020 and 0.7128. Different scenarios such as a recoiling black hole after asymmetric emission of gravitational waves, binary black holes and possible merging systems are proposed for this object. We test these scenarios by comparing our spectra with that fromthe Sloan Digital Sky Survey (SDSS), obtained 4 years prior to our observations. Comparing the redshifts of [Oiii]λλ4960,5008 we put a 3σ limit on the relative acceleration to be less than 32 km s−1 yr −1 between different emitting regions. Using the 2D spectra obtained at different position angles we show that the [Oiii]λ5008 line from the zem = 0.7128 component is extended beyond the spectral point spread function.We infer the linear extent of this line emitting region is ∼ 8 kpc.We also find a tentative evidence for an offset between the centroid of the [Oiii]λ5008 line at zem = 0.7128 and the QSO trace when the slit is aligned at a position angle of 299◦ . This corresponds to the zem = 0.7128 system being at an impact parameter of ∼1 kpc with respect to the zem = 0.6972 in the north west direction. Based on our observations we conclude that the binary black hole model is most unlikely. The spatial extent and the sizes are consistent with both black hole recoil and merging scenarios