Redshift Differences between the Balmer and [O III] λ5007 Lines in High-Redshift Quasars

We present near-infrared spectra of four quasars (QSOs) at z1.5 containing the redshifted Hα, Hβ, and[O III] emission lines. The Hα profile in these objects is redshifted on average by 430±170 km s−1 from the systemic velocity derived from [O III] λ5007. This is considerably larger than the Balmer-line velocity shifts measured for low-redshift objects and is consistent with the trend of increasing redshift differences with increasing continuum luminosity. The rest-frame ultraviolet lines in these objects show large (~1000 km s-1) blueshifts from the systemic velocity, and so the large redshifts for Hα are consistent with the dependence of these redshift differences on ionization potential. These results also show that the systemic velocities of very luminous QSOs are accurately measured only from narrow emission lines.