Metal-Enriched Plasma in Protogalactic Halos: A Survey of N V Absorption in High-z Damped & Sub-Damped Lyman-alpha Systems

Details Metal-Enriched Plasma in Protogalactic Halos: A Survey of N V Absorption in High-z Damped & Sub-Damped Lyman-alpha Systems Metal-Enriched Plasma in Protogalactic Halos: A Survey of N V Absorption in High-z Damped & Sub-Damped Lyman-alpha Systems

2009-05-07

arxiv.org/abs/0905.1042v2

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

26 pages, accepted by Astronomy and Astrophysics, updated with proof changes

Scientific paper

We continue our recent work to characterize the plasma content of high-redshift damped and sub-damped Lyman-alpha systems (DLAs/sub-DLAs), which represent multi-phase gaseous (proto)galactic disks and halos seen toward a background source. We survey N V absorption in a sample of 91 DLAs and 18 sub-DLAs in the redshift range 1.67-2.3. The N V and CIV component b-value distributions in DLAs are statistically similar, but the median b(N V) of 18 km/s is lower than the median b(O VI) of 25 km/s. Some ~20% of the N V components have b<10 km/s 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) N V 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(N V)>14 or log N(O VI)>14.2] that present challenges to either galactic inflow or outflow models.

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