REST-FRAME OPTICAL PROPERTIES OF LUMINOUS 1.5 < Z < 3.5 QUASARS: THE Hβ-[O iii] REGION

Abstract

ABSTRACT We study the rest-frame optical properties of 74 luminous ( L bol = 10 46.2 − 48.2 erg s − 1 ?> ), 1.5 < z < 3.5 ?> broad-line quasars with near-IR (JHK) slit spectroscopy. Systemic redshifts based on the peak of the [O iii] λ5007 line reveal that redshift estimates from the rest-frame UV broad emission lines (mostly Mg ii) are intrinsically uncertain by ∼ 200 km s − 1 ?> (measurement errors accounted for). The overall full-width-at-half-maximum of the narrow [O iii] line is ∼ 1000 km s − 1 ?> on average. A significant fraction of the total [O iii] flux (∼40%) is in a blueshifted wing component with a median velocity offset of ∼ 700 km s - 1 ?> , indicative of ionized outflows within a few kpc from the nucleus; we do not find evidence of significant [O iii] flux beyond ∼ 10 kpc ?> in our slit spectroscopy. The [O iii] line is noticeably more asymmetric and weaker than that in typical less luminous low-z quasars. However, when matched in quasar continuum luminosity, low-z quasars have similar [O iii] profiles and strengths as these high-z systems. Therefore the exceptionally large width and blueshifted wing, and the relatively weak strength of [O iii] in high-z luminous quasars are mostly a luminosity effect rather than redshift evolution. The Hβ-[O iii] region of these high-z quasars displays a similar spectral diversity and Eigenvector 1 correlations with anti-correlated [O iii] and optical Fe ii strengths, as seen in low-z quasars; but the average broad Hβ width is larger by 25% than typical low-z quasars, indicating more massive black holes in these high-z systems. These results highlight the importance of understanding [O iii] in the general context of quasar parameter space in order to understand quasar feedback in the form of [O iii] outflows. The calibrated one-dimensional near-IR spectra are made publicly available, along with a composite spectrum.