Browsing by Author "Andrew, Fox"

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    Metal-Enriched Plasma in Protogalactic Halos: A Survey of N V Absorption in High-z Damped & Sub-Damped Lyman-alpha Systems
    (2009-01-01) Andrew, Fox; Prochaska, Jason X.; Ledoux, C´edric; et al.
    We continue our recent work to characterize the plasma content of high-redshift damped and sub-damped Lyman-α systems (DLAs/sub-DLAs), which represent multi-phase gaseous (proto)galactic disks and halos seen toward a background source. We survey Nv absorption in a sample of 91 DLAs and 18 sub-DLAs in the redshift range 1.67−2.3. The Nv and Civ component b-value distributions in DLAs are statistically similar, but the median b(Nv) of 18 kms −1 is narrower than the median b(Ovi) of ≈25 kms −1 . Some ≈20% of the Nv components have b<10 kms −1 and thus arise in warm, photoionized plasma at log (T/K)<4.92; local sources of ionizing radiation (as opposed to the extragalactic background) are required to keep the cloud sizes physically reasonable. The nature of the remaining ≈80% of (broad) Nv components is unclear; models of radiatively-cooling collisionally-ionized plasma at log (T/K)=5.2–5.4 are fairly successful in reproducing the observed integrated high-ion column density ratios and the component line widths, but we cannot rule out photoionization by local sources. Finally, we identify several unusual DLAs with extremely low metallicity (<0.01 solar) but strong high-ion absorption [logN(Nv)>14 or logN(Ovi)>14.2], which present challenges to either galactic inflow or outflow models.