ar X iv : a st ro - p h / 04 04 59 3 v 1 2 9 A pr 2 00 4 ApJ accepted Fe II Diagnostic Tools for Quasars
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چکیده
The enrichment of Fe, relative to alpha-elements such as O and Mg, represents a potential means to determine the age of quasars and probe the galaxy formation epoch. To explore how Fe II emission in quasars is linked to physical conditions and abundance, we have constructed a 830-level Fe II model atom and investigated through photoionization calculations how Fe II emission strengths depend on non-abundance factors. We have split Fe II emission into three ma-– 2 – emission ratios depend upon hydrogen density and ionizing flux in broad-line regions (BLR's) of quasars. Our calculations show that: 1) similar Fe II(UV)/Mg II ratios can exist over a wide range of physical conditions; 2) the Fe II(UV)/Fe II (Opt1) and Fe II(UV)/Fe II (Opt2) ratios serve to constrain ionizing luminosity and hydrogen density; and 3) flux measurements of Fe II bands and knowledge of ionizing flux provide tools to derive distances to BLR's in quasars. To derive all BLR physical parameters with uncertainties, comparisons of our model with observations of a large quasar sample at low redshift (z < 1) is desirable. The STIS and NICMOS spectrographs aboard the Hubble Space Telescope (HST) offer the best means to provide such observations.
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تاریخ انتشار 2004