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

TL;DR

This study uses spectroscopic observations of a quasar with a damped Lyman-alpha cloud to explore the narrow-line region and extended Lyman-alpha emission, revealing insights into the quasar's environment and gas dynamics.

Contribution

It provides detailed measurements of the DLA cloud's properties and demonstrates the detection of extended Lyman-alpha emission up to 25 kpc, offering new insights into quasar host galaxy environments.

Findings

DLA cloud density between 180-710 cm$^{-3}$ and located 230-580 pc from the quasar.

Extended Lyman-alpha emission detected up to 25 kpc, indicating large-scale gas structures.

Low metallicity suggests gas infall and cold stream accretion near the AGN.

Abstract

We report long-slit spectroscopic observations of the quasar SDSS J082303.22+052907.6 ($z_{\rm CIV}$$\sim$3.1875), whose Broad Line Region (BLR) is partly eclipsed by a strong damped Lyman-$\alpha$ (DLA; log$N$(HI)=21.7) cloud. This allows us to study the Narrow Line Region (NLR) of the quasar and the Lyman-$\alpha$ emission from the host galaxy. Using CLOUDY models that explain the presence of strong NV and PV absorption together with the detection of SiII$^*$ and OI$^{**}$ absorption in the DLA, we show that the density and the distance of the cloud to the quasar are in the ranges 180 $<$ $n_{\rm H}$ $<$ 710 cm$^{-3}$ and 580 $>$ $r_0$ $>$230 pc, respectively. Sizes of the neutral($\sim$2-9pc) and highly ionized phases ($\sim$3-80pc) are consistent with the partial coverage of the CIV broad line region by the CIV absorption from the DLA (covering factor of $\sim$0.85). We show that the residuals are consistent with emission from the NLR with CIV/Lyman-$\alpha$ ratios varying from 0 to 0.29 through the profile. Remarkably, we detect extended Lyman-$\alpha$ emission up to 25kpc to the North and West directions and 15kpc to the South and East. We interpret the emission as the superposition of strong emission in the plane of the galaxy up to 10kpc with emission in a wind of projected velocity $\sim$500kms$^{-1}$ which is seen up to 25kpc. The low metallicity of the DLA (0.27 solar) argues for at least part of this gas being in-falling towards the AGN and possibly being located where accretion from cold streams ends up.