Volume 503, Number 3, September I 2009
|Page(s)||731 - 746|
|Published online||19 May 2009|
A survey of N V absorption in high-z damped and sub-damped Lyman- systems
European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago, Chile e-mail: firstname.lastname@example.org
2 University of California/Lick Observatory, UC Santa Cruz, 1156 High Street, CA 95064, USA
3 Institut d'Astrophysique de Paris, UMR7095 CNRS, UPMC, 98bis Blvd Arago, 75014 Paris, France
4 Center for Astrophysics and Space Sciences, UC San Diego, 9500 Gilman Drive, CA 92093, USA
5 Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganesh Khind, Pune 411 007, India
Accepted: 7 May 2009
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 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 doublet. Our dataset includes high-resolution (6-8 km s-1 FWHM) quasar spectra obtained with VLT/UVES and Keck/HIRES, together with medium-resolution (≈40 km s-1 FWHM) quasar spectra from Keck/ESI. In DLAs, we find eight secure detections, four marginal detections, and 79 non-detections, for which we place 3σ upper limits on the column density. The detection rate of in DLAs is therefore %. Two sub-DLA detections are found among a sample of 18, at a similar detection rate of %. We show that the detection rate is a strong function of neutral-phase nitrogen abundance, increasing by a factor of ≈4 at [N/H] = [/] > -2.3. The and component b-value distributions in DLAs are statistically similar, but the median b() of 18 km s-1 is narrower than the median b() of ≈25 km s-1. Some ≈20% of the components have km s-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) 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 (log N() > 14 or log N() > 14.2), which present challenges to either galactic inflow or outflow models.
Key words: quasars: absorption lines / cosmology: observations / galaxies: high-redshift / galaxies: halos / galaxies: ISM
Based on observations taken with the Ultraviolet and Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) Unit 2 (Kueyen) at Paranal, Chile, operated by the European Southern Observatory (ESO), and with the High Resolution Echelle Spectrograph (HIRES) and Echelle Spectrograph and Imager (ESI) instruments located at the W. M. Keck Observatory on Mauna Kea, Hawaii.
© ESO, 2009
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