AGN Physics

The Mg II 2800 A broad emission line in the IR can be used to determine black hole masses and Eddington ratios for the quasars in our sample with z < 3.7 and 4.4 < z < 5.2. Most previous studies at z > 2 have used the C IV 1550 A emission line for this purpose (e.g., Vestergaard & Peterson 2006). However, the likely non-virial motions involved in the line's emission introduce substantial uncertainties and possible systematic biases (Baskin & Laor 2005). Our measurements of MBH based on Mg II at high z will not only be more accurate than previous work, they will also for the first time allow direct comparisons of MBH across a wide range of redshifts using the same emission line diagnostic. The observations will also provide QSO metallicities and measurements of Fe II/Mg II (an indicator of chemical enrichment timescale) in various transmission windows at z > 3.5 where only a few dozen measurements in heterogenous samples exist (e.g. Kurk et al. 2007). The unique aspect of this study will be comparisons between metallicity indicators and accurate measurements of MBH, L/Led and Fe II/Mg II in the same quasar sample. We will, in particular, investigate claims that the metallicity correlates with 1) MBH as part of a general mass-metallicity relation in quasar hosts (Warner et al. 2004, 2) L/Led as part of evolutionary trend with quasar age (Shemmer et al. 2004).