A faint M$_{\rm UV} = -14.5$ Lyman-continuum leaker candidate in the epoch of reionization: Unprecedented Ly$α$ properties at z=5.725
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| Main Authors: | , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | 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. |
| author_facet | 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. |
| contents | We report the unprecedented Ly$α$ properties of AMORE6, an extremely metal-poor ($12+\log({\rm O/H}) < 6$), low-mass ($M_\star = 4.4\times10^{5}\,M_\odot$), and ultracompact (effective radius $\sim30$ pc) dwarf galaxy at $z=5.7253$, which is gravitationally lensed by the cluster A2744. A prominent, narrow, and nearly symmetric Ly$α$ emission line is detected at the systemic redshift (the latter traced by H$β$, from JWST/NIRCam slitless spectroscopy), with a rest-frame equivalent width of $150 \pm 10$ Å, a full width at half maximum of $\rm 58\pm1$ km s$^{-1}$, and a slight asymmetry, resulting in a flux excess of $\rm \sim10\%$ in the red wing of the line. The negligible velocity offset from systemic ($dv = 4\pm67$ 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 (Ly$α$), AMORE6 stands out as one of the most compelling LyC-leaking candidates yet discovered in the epoch of reionization. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2512_16728 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A faint M$_{\rm UV} = -14.5$ Lyman-continuum leaker candidate in the epoch of reionization: Unprecedented Ly$α$ properties at z=5.725 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. Astrophysics of Galaxies We report the unprecedented Ly$α$ properties of AMORE6, an extremely metal-poor ($12+\log({\rm O/H}) < 6$), low-mass ($M_\star = 4.4\times10^{5}\,M_\odot$), and ultracompact (effective radius $\sim30$ pc) dwarf galaxy at $z=5.7253$, which is gravitationally lensed by the cluster A2744. A prominent, narrow, and nearly symmetric Ly$α$ emission line is detected at the systemic redshift (the latter traced by H$β$, from JWST/NIRCam slitless spectroscopy), with a rest-frame equivalent width of $150 \pm 10$ Å, a full width at half maximum of $\rm 58\pm1$ km s$^{-1}$, and a slight asymmetry, resulting in a flux excess of $\rm \sim10\%$ in the red wing of the line. The negligible velocity offset from systemic ($dv = 4\pm67$ 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 (Ly$α$), AMORE6 stands out as one of the most compelling LyC-leaking candidates yet discovered in the epoch of reionization. |
| title | A faint M$_{\rm UV} = -14.5$ Lyman-continuum leaker candidate in the epoch of reionization: Unprecedented Ly$α$ properties at z=5.725 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2512.16728 |