Infrared Spectroscopy of the Gravitationally Lensed Quasar B1422+231: Mg [CSC]ii[/CSC] λ2798 and Fe [CSC]ii[/CSC] Emission from the Broad-Line Gas at [ITAL]z[/ITAL] = 3.62

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Abstract
The rest-frame UV-optical (2000-5300 Å) spectrum of the gravitationally lensed flat-spectrum radio-loud quasar B1422+231 system at z = 3.62 is presented. The spectrum is similar to the Large Bright Quasar Survey (LBQS) composite spectrum (Francis et al.), which indicates no significant UV-optical spectral evolution in some quasars at 0 < z < 3.6. The Fe II(UV + optical)/Mg II λ2798 flux ratio is 12.2 ± 3.9, which is comparable to 8.9 for the LBQS composite spectrum of quasars at z = 1-2 analyzed in this work, and 7.8 ± 2.6 for quasars at z = 0.15-0.63 analyzed by Wills, Netzer, & Wills. It is concluded that the majority of stars in the host galaxy of B1422+231 have formed much earlier (~1.5 Gyr) than z = 3.6. The first detection of [O III] λ5007 in a quasar beyond z = 3 is also reported.