2009/05/19 by Andrew J. Fox, J. X. Prochaska, J. Xavier Prochaska +7
Physics and Astronomy · #Absorption (acoustics) #Astrophysics #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Galaxy #Halo #Metallicity #Optics #Physics #Plasma #Quasar #Redshift #Stellar, planetary, and galactic studies #astro-ph.CO
paper · pdf · doi:10.1051/0004-6361/200911717
26 pages, accepted by Astronomy and Astrophysics, updated with proof changes
openalex publication_date 2009/05/19 · arxiv created 2009/06/23 · arxiv updated 2015/05/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We continue our recent work of characterizing the plasma content of high-redshift damped and sub-damped Lyman-<i>α<i/> 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 < <i>z<i/><sub>abs<sub/> < 4.28 with unblended coverage of the doublet. Our dataset includes high-resolution (6-8 km s<sup>-1<sup/> <i>FWHM<i/>) quasar spectra obtained with VLT/UVES and Keck/HIRES, together with medium-resolution (<i>≈<i/>40 km s<sup>-1<sup/> <i>FWHM<i/>) quasar spectra from Keck/ESI. In DLAs, we find eight secure detections, four marginal detections, and 79 non-detections, for which we place 3<i>σ<i/> 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 <i>≈<i/>4 at [N/H] = [/] > -2.3. The and component <i>b<i/>-value distributions in DLAs are statistically similar, but the median <i>b<i/>() of 18 km s<sup>-1<sup/> is narrower than the median <i>b<i/>() of <i>≈<i/>25 km s<sup>-1<sup/>. Some <i>≈<i/>20% of the components have km s<sup>-1<sup/> and thus arise in warm, photoionized plasma at log (<i>T<i/>/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 <i>≈<i/>80% of (broad) components is unclear; models of radiatively-cooling collisionally-ionized plasma at log (<i>T<i/>/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 <i>N<i/>() > 14 or log <i>N<i/>() > 14.2), which present challenges to either galactic inflow or outflow models.