An extremely metal-poor Lyman $\alpha$ emitter candidate at $z=6$ revealed through absorption spectroscopy

TL;DR

This paper reports the discovery of a candidate extremely metal-poor Lyman alpha emitter at redshift 6, found near a quasar, offering insights into early galaxy formation and Population III stars.

Contribution

It presents the first detection of a metal-poor Lyman alpha emitter in the vicinity of a high-redshift quasar using archival VLT/MUSE data, highlighting a new method for identifying such systems.

Findings

Detected Lyα emission at z=6.0323 aligned with quasar proximity zone.

Metallicity constraint of [Z/H] < -3 indicating an extremely metal-poor system.

Potential site for studying signatures of Population III stars.

Abstract

We report the discovery of a Lyman $\alpha$ emitter (LAE) candidate in the immediate foreground of the quasar PSO J158-14 at $z_{\rm QSO}=6.0685$ at a projected distance $\sim29\ {\rm pkpc}$ that is associated with an extremely metal-poor absorption system. This system was found in archival observations of the quasar field with the Very Large Telescope/Multi-Unit Spectroscopic Explorer (VLT/MUSE) and was previously missed in searches of absorption systems using quasar absorption line spectroscopy as it imparts no detectable metal absorption lines on the background quasar spectrum. The detected Ly$\alpha$ emission line at a redshift of $z_{\rm LAE}=6.0323$ is well aligned with the outer edge of the quasar's proximity zone and can plausibly cause its observed damping wing if it is associated with a proximate sub-damped Ly$\alpha$ absorption system with a column density of $\log {N_{\rm HI} / {\rm cm}^{-2}} \approx 19.7$. A $>10$ hour medium-resolution spectrum of the quasar observed with the Magellan/Folded-port InfraRed Echellette (FIRE) and VLT/X-Shooter spectrographs reveals a metallicity constraint of ${\rm [Z/H]} < -3$. Such low metallicity makes this system an extremely metal-poor galaxy candidate and provides an exciting site to study possible signatures of Population III stars.