A faint M_UV = −14.5 Lyman-continuum leaker candidate in the epoch of reionization: Unprecedented Lyα properties at z = 5.725

March 2026 • 2026A&A...708L...2M

Authors • Messa, M. • Vanzella, E. • Morishita, T. • Stiavelli, M. • Treu, T. • Bergamini, P. • Liu, Z. • Zanella, A. • Bolamperti, A. • Verhamme, A. • Garel, T. • Grillo, C. • Rosati, P.

Abstract • We report the unprecedented Lyα properties of AMORE6, an extremely metal-poor (12 + log(O/H) < 6), low-mass (M_★ = 4.4 × 10⁵ M_⊙), and ultracompact (effective radius ∼30 pc) dwarf galaxy at z = 5.7253, which is gravitationally lensed by the cluster A2744. A prominent, narrow, and nearly symmetric Lyα emission line is detected at the systemic redshift (the latter traced by Hβ, from JWST/NIRCam slitless spectroscopy), with a rest-frame equivalent width of 150 ± 10 Å, a full width at half maximum of 58 ± 1 km s⁻¹, and a slight asymmetry, resulting in a flux excess of ∼10% in the red wing of the line. The negligible velocity offset from systemic (dv = 4 ± 67 km s⁻¹, 3σ uncertainty), together with the sharpness and symmetry of the profile, indicates minimum radiative transfer effects, which implies a neutral hydrogen column density consistent with an optically thin medium that in turn is compatible with a nonzero ionizing photon escape fraction. If indirect spectral diagnostics calibrated at z < 4.5 remain the only viable tools for identifying LyC leakers during reionization, then based on its strongest indicator (Lyα), AMORE6 stands out as one of the most compelling LyC-leaking candidates yet discovered in the epoch of reionization.

Links

• POSTSCRIPT https://www.aanda.org/10.1051/0004-6361/202558660/postscript
• PDF https://www.aanda.org/10.1051/0004-6361/202558660/pdf
• PREPRINT http://arxiv.org/abs/2512.16728
• ELECTR https://doi.org/10.1051%2F0004-6361%2F202558660