Browsing by Author "Fox, Andrew J."

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C iv absorption in damped and sub-damped Lyman-alpha systems: Correlations with metallicity and implications for galactic winds at z~2-3
(2007-07-27) Fox, Andrew J.; Ledoux, C.; Petitjean, Patrick; et al.
We present a study of Civ absorption in a sample of 63 damped Lyman-α (DLA) systems and 11 sub-DLAs in the redshift range 1.75
Hot Halos around High Redshift Protogalaxies: Observations of O VI and N V Absorption in Damped Lyman Alpha systems
(2007-01-15) Fox, Andrew J.; Petitjean, Patrick; Ledoux, C´edric; et al.
Aims. We present a study of the highly ionized gas (plasma) associated with damped Lyman-α (DLA) systems at z=2.1–3.1. Methods. We search for Ovi absorption and corresponding Si iv, Civ, and Nv in a Very Large Telescope/Ultraviolet-Visible Echelle Spectrograph (VLT/UVES) sample of 35 DLA systems with data covering Ovi at S/N>10. We then use optical depth proﬁle comparisons and ionization modelling to investigate the properties, phase structure, and origin of the plasma. Results. We report twelve DLAs (nine intervening and three at <5 000 kms −1 from the QSO redshift) with detections of Ovi absorption. There are no clear Ovi non-detections, so the incidence of Ovi in DLAs is between 34% (12/35) and 100%. Among these 12 DLAs, Civ and Si iv are seen whenever data is available, and Nv is detected in 3 cases. Analysis of the line widths together with photoionization modelling suggests that two phases of DLA plasma exist: a hot, collisionally ionized phase (seen in broad Ovi components), and a warm, photoionized phase (seen just in narrow Civ and Si iv components). The presence of inﬂows and/or outﬂows is indicated by individual Ovi and Civ components displaced from the neutral gas (either blueshifted or redshifted) by up to 400 kms −1 . We ﬁnd tentative evidence (98% conﬁdence) for correlations between the DLA metallicity (measured in the neutral gas) and high-ion column density, and between the DLA metallicity and high-ion line width, as would be expected if supernova-driven galactic outﬂows rather than accretion produced the high ions. Using conservative ionization corrections, we ﬁnd lower limits to the total hydrogen column densities in the hot (Ovi-bearing) and warm (Civ-bearing) phases in the range logNHot H ii > 19.5 to > 21.1, and logNWarm H ii > 19.4 to > 20.9. On average, the hot and warm phases thus contain > ∼40% and > ∼20% of the baryonic mass of the neutral phase in DLAs, respectively. Conclusions. If the temperature in the Ovi phase is ≈ 106 K and so fOvi = Ovi/O ≪ 0.2, the plasma can make a signiﬁcant contribution to the metal budget at high redshift. Additional searches for Ovi in Lyman Limit Systems (QSO absorbers with 17.0 < NHi < 20.3) will be necessary to determine the total quantity of baryons and metals hidden in hot halos at z ≈ 2.
Multiphase plasma in sub-damped Lyman-Alpha systems : A hidden metal reservoir
(2007-08-22) Fox, Andrew J.; Petitjean, Patrick; Ledoux, C.; et al.
We present a VLT/UVES spectrum of a proximate sub-damped Lyman-α (sub-DLA) system at zabs = 2.65618 toward the quasar Q0331-4505 (zqso = 2.6785±0.0030). Absorption lines of O I, Si II,Si III, Si IV, C II, C III, C IV, Fe II, Al II, and O VI are seen in the sub-DLA, which has a neutral hydrogen column density logNHI = 19.82 ± 0.05. The absorber is at a velocity of 1 820 ± 250 kms−1 from the quasar; however, its low metallicity [O/H]=−1.64 ± 0.07, lack of partial coverage, lack of temporal variations between observations taken in 2003 and 2006, and non-detection of N V imply the absorber is not a genuine intrinsic system. By measuring the O VI column density and assuming equal metallicities in the neutral and ionized gas, we determine the column density of hot ionized hydrogen in this sub-DLA, and in two other sub-DLAs with O VI drawn from the literature. Coupling this with determinations of the typical amount of warm ionized hydrogen in sub-DLAs, we conﬁrm that sub-DLAs are a more important metal reservoir than DLAs, in total comprising at least 6–22% of the metal budget at z ≈ 2.5.