Discovery of a Lyα-emitting Dark Cloud within the z ̃ 2.8 SMM J02399-0136 System

Author(s): Li, Qiong; Cai, Zheng; Prochaska, J Xavier; Battaia, Fabrizio Arrigoni; Ivison, RJ; Falgarone, Edith; Cantalupo, Sebastiano; Matuszewski, Mateusz; Neill, James Don; Wang, Ran; Martin, Chris; Moore, Anna | Abstract: © 2019. The American Astronomical Society. All rights reserved. We present Keck/Keck Cosmic Web Imager (KCWI) integral field spectrograph observations of the complex system surrounding SMM J02399-0136 (a lensed z = 2.8 sub-mm galaxy), including an associated Lyα nebula, a dust-obscured, broad-absorption-line quasar, and neighboring galaxies. At a 3σ surface brightness contour of 1.6 × 10-17 erg s-1 cm-2 arcsec-2, the Lyα nebula extends over 17 arcsec (≈140 physical kpc) and has a total Lyα luminosity of (uncorrected for lensing). The nebula exhibits a kinematic shear of over 100 pkpc with lowest velocities east of SMM J02399-0136 and increasing to the southwest. We also discover a bright, Lyα emitter, separated spatially and kinematically from the nebula, at a projected separation of ≈60 kpc from the quasar. This source has no clear central counterpart in deep Hubble Space Telescope imaging, giving an intrinsic Lyα rest-frame equivalent width greater than 312 A (5σ). We argue that this "dark cloud" is illuminated by the quasar with a UV flux that is orders of magnitude brighter than the emission along our sightline. This result confirms statistical inferences that luminous quasars at z l 2 emit UV radiation anisotropically. Future KCWI observations of other lines, e.g., Lyβ, He ii, C iv, etc, and with polarimetry will further reveal the origin of the Lyα nebula and nature of the dark cloud.