Fox, A. J. ; Prochaska, J. X. ; Ledoux, C. ; Petitjean, P. ; Wolfe, A. M. ; Srianand, R. (2009) Metal-enriched plasma in protogalactic halos - A survey of N V absorption in high-z damped and sub-damped Lyman-α systems Astronomy and Astrophysics, 503 (3). pp. 731-746. ISSN 0004-6361
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Official URL: http://www.aanda.org/articles/aa/abs/2009/33/aa117...
Related URL: http://dx.doi.org/10.1051/0004-6361/200911717
Abstract
We continue our recent work of characterizing 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 < Zabs < 4.28 with unblended coverage of the NV doublet. Our dataset includes high-resolution (6-8 kms-1 FWHM) quasar spectra obtained with VLT/UVES and Keck/HIRES, together with medium-resolution (≈ 40 kms-1 FWHM) quasar spectra from Keck/ESI. In DLAs, we find eight secure NV detections, four marginal detections, and 79 non-detections, for which we place 3σ upper limits on the NV column density. The detection rate of NV in DLAs is therefore 13+5-4%. Two sub-DLA NV detections are found among a sample of 18, at a similar detection rate of 11+15-7%. We show that the NV detection rate is a strong function of neutral-phase nitrogen abundance, increasing by a factor of ≈ 4 at [N/H] = [NI/HI] > -2.3. The NV and CIVcomponent 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 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.
Item Type: | Article |
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Source: | Copyright of this article belongs to EDP Sciences. |
Keywords: | Quasars; Absorption Lines; Cosmology; Observations; Galaxies; High-redshift; Galaxies; Halos; Galaxies; ISM |
ID Code: | 55268 |
Deposited On: | 18 Aug 2011 08:15 |
Last Modified: | 18 May 2016 07:36 |
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