Strong Ly alpha Emission in the Proximate Damped Ly alpha Absorption Trough toward the Quasar SDSS J095253.83+011422.0

TL;DR

This paper reveals that the absence of broad Ly alpha emission in a specific quasar is due to a proximate damped Ly alpha absorber, which acts as a natural coronagraph, allowing the study of quasar outflows and surrounding gas.

Contribution

It demonstrates that dark PDLA absorption causes the missing broad Ly alpha emission and provides new insights into quasar feedback and the properties of the absorbing gas.

Findings

Identification of a dark PDLA causing the Ly alpha emission suppression

Residual Ly alpha emission is two orders of magnitude stronger than previously observed

PDLA acts as a natural coronagraph revealing quasar outflow gas

Abstract

SDSS J095253.83+011422.0 (SDSS J0952+0114) was reported by Hall et al. (2004) as an exotic quasar at $z_{\rm em}=3.020$. In contrast to prominent broad metal--line emissions with FWHM~9000 km/s, only a narrow Ly \alpha emission line is present with FWHM~1000 km/s. The absence of broad Ly alpha emission line has been a mystery for more than a decade. In this paper, we demonstrate that this is due to dark Proximate Damped Ly alpha Absorption (PDLA) at $z_{\rm abs}=3.010$ by identifying associated Lyman absorption line series from the damped Ly beta up to Ly9, as well as the Lyman limit absorption edge. The PDLA cloud has a column density of $\log N_{\rm H\,I}({\rm cm}^{-2})=21.8\pm0.2$, a metallicity of [Zn/H]$>-1.0$, and a spatial extent exceeding the Narrow Emission Line Region (NELR) of the quasar. With a luminosity of $L_{{\rm Ly}\alpha}\sim10^{45}$ erg s$^{-1}$, the residual Ly alpha emission superposed on the PDLA trough is of two orders of magnitude stronger than previous reports. This is best explained as re-radiated photons arising from the quasar outflowing gas at a scale larger than the NELR. The PDLA here, acting like a natural coronagraph, provides us with a good insight into the illuminated gas in the vicinity of the quasar, which are usually hard to resolve due to their small size and "seeing fuzz" of bright quasars. Notably, SDSS J0952+0114 analogs might be easily omitted in the spectroscopic surveys of DLAs and PDLAs, as their damped Ly alpha troughs can be fully filled by additional strong Ly alpha emissions. Our preliminary survey shows that such systems are not very rare. They are potentially a unique sample for probing strong quasar feedback phenomena in the early universe.