Infrared spectroscopic confirmation of z ∼ 2 photometrically selected obscured quasars

Abstract

The census of obscured quasar populations is incomplete and remains a major unsolved problem, especially at higher redshifts, where we expect a greater density of galaxy formation and quasar activity. We present Gemini GNIRS near-infrared spectroscopy of 24 luminous obscured quasar candidates from the Sloan Digital Sky Survey’s Stripe 82 region. The targets were photometrically selected using a WISE/W4 selection technique that is optimized to identify IR-bright and heavily reddened/optically obscured targets at z > 1. We detect emission lines of Hα, Hβ, and/or [O III] in 23 sources allowing us to measure spectroscopic redshifts in the range 1 < z < 3 with bolometric luminosities spanning L = 1046.3–1047.3 erg s-1. We observe broad 103–104 km s-1 Balmer emissions with large Hα/Hβ ratios, and we directly observe a heavily reddened rest-frame optical continuum in several sources, suggesting high extinction (AV ∼ 7–20 mag). Our observations demonstrate that such optical/infrared photometric selection successfully recovers high-redshift obscured quasars. The successful identification of previously undetected red, obscured high-redshift quasar candidates suggests that there are more obscured quasars yet to be discovered.