A coronagraphic absorbing cloud reveals the narrow-line region and extended Lyman α emission of QSO J0823+0529

Abstract : We report long-slit spectroscopic observations of the quasar SDSS J082303.22+052907.6 (z_{C IV}} ∼ 3.1875), whose broad-line region (BLR) is partly eclipsed by a strong damped Lyman α (DLA; logN(H I) = 21.7) cloud. This allows us to study the narrow-line region (NLR) of the quasar and the Lyman α emission from the host galaxy. Using CLOUDY models that explain the presence of strong N V and P V absorption together with the detection of Si II* and O I** absorption in the DLA, we show that the density and the distance of the cloud to the quasar are in the ranges 180 < n_H < 710 cm^-3 and 580 > r₀ > 230 pc, respectively. Sizes of the neutral (∼2-9pc) and highly ionized phases (∼3-80pc) are consistent with the partial coverage of the C IV BLR by the C IV absorption from the DLA (covering factor of ∼0.85). We show that the residuals are consistent with emission from the NLR with C IV/Lyman α ratios varying from 0 to 0.29 through the profile. Remarkably, we detect extended Lyman α emission up to 25 kpc to the north and west directions and 15 kpc to the south and east. We interpret the emission as the superposition of strong emission in the plane of the galaxy up to 10 kpc with emission in a wind of projected velocity ∼500 km s^-1 which is seen up to 25 kpc. The low metallicity of the DLA (0.27 solar) argues for at least part of this gas being infalling towards the active galactic nucleus and possibly being located where accretion from cold streams ends up.