Establish the interpretation of J0217−0208’s broad Balmer component

Determine whether the broad Hα and Hβ components of the z=6.20 source J0217−0208 originate in the broad-line region of an active galactic nucleus or instead arise from outflowing gas in a star-forming galaxy.

Background

J0217−0208 has Balmer profiles dominated by narrow emission, and its classification depends on how the broad and outflow components are modeled. The authors’ fiducial fit favors a broad-line-region interpretation through a lower Bayesian Information Criterion, but alternative fitting frameworks assign some of the same flux to outflowing gas.

The authors therefore retain the source as a broad-line quasar for their fiducial analysis while explicitly acknowledging that it could instead be a star-forming galaxy with outflowing gas. The classification remains unresolved because the line decomposition is model dependent.