Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7988h&link_type=abstract
HST Proposal ID #7988
Astronomy and Astrophysics
Astrophysics
Hst Proposal Id #7988 Extragalactic Astrophysics
Scientific paper
Estimates of the heavy-element abundances in QSOs/AGNs can yield important constraints on star formation and galactic nuclear evolution at high redshifts. Our own recent studies indicate that QSO metallicities are typically solar or higher, with a tentative trend for greater metallicities in more luminous objects. The high metallicities are consistent with the rapid, early-epoch star formation expected in massive galactic nuclei, while the trend with luminosity might derive from a mass-metallicity relationship among QSO host galaxies. Further study is now needed to quantify the observational trends with L and z and test the abundance estimates with better data and more diagnostics. The broad emission lines are vital for this work because they can be measured in large QSO/AGN samples. We propose an HST archive program to compare the broad emission-line properties of z< 1 QSOs/AGNs in the HST database with QSOs at z 2, z 3 and z> 4 in existing high-quality, ground-based data sets. Our emphasize will be on the abundance issues, but this work will also naturally address various problems concerning the QSOs themselves, such as {1} the redshift evolution of their environments, {2} the location, geometry and physical conditions in the emission- line regions, and {3} the influence of metallicity and luminosity on the nebular physics in general and on the empirical ``Baldwin effect'' in particular.
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