4. GENERAL ABUNDANCE SUMMARY
The main abundance results are as follows.
- There is a growing consensus from the BELs and NALs
for Z
Z
in
QSOs out to z > 4. The upper limits on the
metallicities are not well known, but none of the data
require Z > 10
Z. Solar
to a few times solar metallicity appears to be typical. Based on very
limited data, there is no evidence for a decline at the highest
redshifts.
- A trend in the NV/HeII and NV/CIV BEL ratios suggests
that the metallicities are generally higher in more luminous QSOs.
- The BELs and NALs both suggest that the relative nitrogen abundance
(e.g. N/C and N/O) is typically solar or higher. We will argue below
(Section 6) that this result corroborates the
evidence for Z
Z
(because of the likely secondary origin of nitrogen at these
metallicities).
- There is tentative evidence for super-solar Fe/Mg abundances out
to z > 4 based on the FeII/MgII BEL strengths. Again, based on
limited data, there is no evidence for a decline in this ratio at
the highest redshifts.
- The extremely high metallicities and large P/C ratios derived so far
from the BALs are probably incorrect. In further support of that
conclusion, we note that BELR simulations with the nominally derived BAL
abundances [including large enhancements in P and other odd-numbered
elements like Al
(Shields 1996)]
are inconsistent with observed BEL
spectra (based on unpublished work in collaboration with G
Shields).