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Metal-Enriched Plasma in Protogalactic Halos: A Survey of N V Absorption in High-z Damped & Sub-Damped Lyman-alpha Systems | | Andrew J. Fox
; J. Xavier Prochaska
; Cédric Ledoux
; Patrick Petitjean
; Arthur M. Wolfe
; Raghunathan Srianand
; | | Date: |
7 May 2009 | | Abstract: | 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<z<4.28 with unblended coverage of the N V
doublet, using data from VLT/UVES, Keck/HIRES, and Keck/ESI. In DLAs, we find
eight secure N V detections, four marginal detections, and 79 non-detections.
The detection rate of N V in DLAs is therefore 13+/-4%. Two sub-DLA N V
detections are found among a sample of 18, at a similar detection rate of
11+/-8%. We show that the N V detection rate is a strong function of
metallicity, increasing by a factor of ~4 at [N/H]=[NI/HI]>-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. | | Source: | arXiv, 0905.1042 | | Services: | Forum | Review | PDF | Favorites | |
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