Near-infrared spectra and intrinsic luminosities of candidate Type II quasars at 2 < z < 3.4

Abstract

We present JHK near-infrared (NIR) spectroscopy of 25 candidate Type II quasars selected from the Sloan Digital Sky Survey (SDSS), using Triplespec on the Apache Point Observatory 3.5 m telescope, the Folded-port InfraRed Echellette at the Magellan/Baade 6.5 m telescope, and the Gemini Near-Infrared Spectrograph on Gemini. At redshifts of 2 < z < 3.4, our NIR spectra probe the rest-frame optical region of these targets, which were initially selected to have strong lines of C IV and Ly α, with FWHM < 2000 km s -1 from the SDSS pipeline. We use the [O III] λ5007 line shape as a model for the narrow-line region emission and find that Hα consistently requires a broad component with FWHMs ranging from 1000 to 7500 km s-1. Interestingly, the C IV lines also require broad bases, but with considerably narrower widths of 1000-4500 km s-1. Estimating the extinction using the Balmer decrement and also the relationship in lower-z quasars between rest equivalent width and luminosity in the [O III] line, we find typical AV values of 0-2 mag, which naturally explains the attenuated C IV lines relative to Hα. We propose that our targets are moderately obscured quasars. We also describe one unusual object with three distinct velocity peaks in its [O III] spectrum. © 2014. The American Astronomical Society. All rights reserved..