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New observations of iron emission in high redshift QSOs indicate significant heavy element synthesis at very early epochs. We have identified Fe~II emission near the Mg~II~$\lambda2798$ broad emission line in 3 QSOs with $z \sim 4.5$, using near-infrared spectroscopy at KPNO and CTIO. Since iron is thought to be produced primarily in supernovae type Ia, which take about 1 Gyr to begin enrichment of the ISM, strong constraints can be put on cosmological parameters if we require SN Ia as the source of iron.
Our previous observations have indicated strong optical Fe~II in QSOs with redshifts up to $z = 3.4$, which begins to put constraints on cosmological models since the combination of H$_o = 100$ km/s/Mpc and q$_o = 0.5$ gives an age of $\sim 0.7$ Gyr at that redshift. Significant iron at a redshift of 4.5 is inconsistent with any H$_o \stackrel{\textstyle >}{\sim} 50$ if q$_o = 0.5$, and limits q$_o \leq 0.15$ for the more popular value of H$_o = 85$.
Further analysis and observations of these high redshift QSOs should address the issue of the source of the iron, since SN Ia and the much faster-evolving SN II synthesize elements with very different ratios. In any event, the early and rapid star formation required to produce the large abundance of iron supports the notion that luminous QSOs are hosted by massive galaxies.
