Browsing by Author "Pettini, M"

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    The CIV mass density of the universe at redshift 5
    (2003) Pettini, M; Madau, P; Bolte, M; Prochaska, JX; Ellison, SL; Fan, XH
    In order to search for metals in the Lyalpha forest at redshifts z(abs) > 4, we have obtained spectra of high signal-to-noise ratio and moderately high resolution of three QSOs at z(em) > 5: 4 discovered by the Sloan Digital Sky Survey. These data allow us to probe to metal enrichment of the intergalactic medium at early times with higher sensitivity than previous studies. We find 16 C IV absorption systems with column densities log N (C IV) = 12.50-13.98 over a total redshift path DeltaX = 3.29. In the redshift interval z = 4.5-5.0, where our statistics are most reliable, we deduce a comoving mass density of C3+ ions Omega(CIV) = (4.3 +/- 2.5) x 10(-8) ( 90% confidence limits) for absorption systems with log N (C-IV) greater than or equal to 13.0 ( for an Einstein - de Sitter cosmology with h = 0.65). This value of Omega(CIV) is entirely consistent with those measured at z < 4; we confirm the earlier finding by Songaila that neither the column density distribution of C iv absorbers nor its integral show significant redshift evolution over a period of time that stretches from similar to 1.25 to similar to 4.5 Gyr after the big bang. This somewhat surprising conclusion may be an indication that the intergalactic medium was enriched in metals at z >> 5, perhaps by the sources responsible for its reionization. Alternatively, the C iv systems we see may be associated with outflow from massive star- forming galaxies at later times, while the truly intergalactic metals may reside in regions of the Ly alpha forest of lower density than those probed up to now.
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    The sizes and kinematic structure of absorption systems towards the lensed quasar APM08279+5255
    (2004) Ellison, SL; Ibata, R; Pettini, M; Lewis, GF; Aracil, B; Petitjean, P; Srianand, R
    We have obtained spatially resolved spectra of the z(em)=3.911 triply imaged QSO APM08279+5255 using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). We study the line of sight equivalent width (EW) differences and velocity shear of high and low ionization absorbers (including a damped Lyman alpha [DLA] system identified in a spatially unresolved ground based spectrum) in the three lines of sight. The combination of a particularly rich spectrum and three sight-lines allow us to study 27 intervening absorption systems over a redshift range 1.180%) over kpc scales. A minimum radius for strong (EW>0.3Angstrom) Mg II systems of >1.4 h(70)(-1) kpc is inferred from absorption coincidences in all lines of sight. For weak Mg II absorbers (EW<0.3 angstrom), a maximum likelihood analysis indicates a most probable coherence scale of 2.0 h(70)(-1) kpc for a uniform spherical geometry, with 95% confidence limits ranging between 1.5 and 4.4 h(70)(-1) kpc. The weak Mg II absorbers may therefore represent a distinct population of smaller galaxies compared with the strong Mg II systems which we know to be associated with luminous galaxies whose halos extend over tens of kpc. Alternatively, the weak systems may reside in the outer parts of larger galaxies, where their filling factor may be lower. By cross-correlating spectra along different lines of sight, we infer shear velocities of typically less than 20 km s(-1) for both high and low ionization absorbers. Finally, for systems with weak absorption that can be confidently converted to column densities, we find constant N(C IV)/N(Si IV) across the three lines of sight. Similarly, the [Al/Fe] ratios in the z(abs)=2.974 DLA are consistent with solar relative abundances over a transverse distance of similar to0.35 h(70)(-1) kpc.