Lyman-alpha haloes in the aftermath of reionisation
Abstract
We present a comparative study of Lyα haloes (LAHs) around low-luminosity (LLyα≲ 1042 erg s−1) Lyα-emitting galaxies (LAEs) at very high redshifts z≥6 and a reference sample at z∼ 3 covering a similar Lyα luminosity and host galaxy stellar mass range. Using data from the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO VLT, we extracted the samples such that at the different redshifts we obtain the same intrinsic surface brightness sensitivity, accounting for cosmological dimming. We detect extended Lyα emission around 6 out of 18 high-z LAEs in the MUSE eXtremely Deep Field (MXDF), more than doubling the number of known such objects at z≥6. We obtain an only slightly higher individual LAH detection fraction of 40% among the lower redshift comparison sample. Yet the typical exponential scale lengths at z≥6 are three times smaller than those at z∼3. Stacking the LAEs with undetected haloes gives again drastically different results for the two samples, with a highly significant halo detection at z∼ 3 but no trace of extended Lyα emission at z≥6. We also find the Lyα spectral line widths of the high-z sample to be ∼2.5 smaller in comparison to the lower redshift objects. We discuss the potential mechanisms driving such strong changes. In a reionisation-driven scenario the higher neutral fraction in the intergalactic and circumgalactic media might lead to substantial scattering losses of escaping Lyα radiation, leaving detectable only emission from the vicinity of the star-forming regions. In an alternative scenario the LAH properties might be linked more closely to the evolution of their host galaxies than previously thought.
Versions
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BibTeX
@misc{smirnov2026lymanalpha,
title = {{Lyman-alpha haloes in the aftermath of reionisation}},
author = {Daniil Smirnov and Lutz Wisotzki and Tanya Urrutia and John Pharo and Ramona Augustin and Yucheng Guo and Daria Kozlova and Haruka Kusakabe and Jorryt Matthee and Ismael Pessa and Joop Schaye},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2607.05087},
eprint = {2607.05087},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.05087},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Lyman-alpha haloes in the aftermath of reionisation
AU - Daniil Smirnov
AU - Lutz Wisotzki
AU - Tanya Urrutia
AU - John Pharo
AU - Ramona Augustin
AU - Yucheng Guo
AU - Daria Kozlova
AU - Haruka Kusakabe
AU - Jorryt Matthee
AU - Ismael Pessa
AU - Joop Schaye
PY - 2026
DA - 2026/11/02
PB - arXiv
DO - 10.48550/arxiv.2607.05087
UR - https://arxiv.org/abs/2607.05087
AB - We present a comparative study of Lyα haloes (LAHs) around low-luminosity (L_Lyα≲ 10^42 erg s^−1) Lyα-emitting galaxies (LAEs) at very high redshifts z≥6 and a reference sample at z∼ 3 covering a similar Lyα luminosity and host galaxy stellar mass range. Using data from the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO VLT, we extracted the samples such that at the different redshifts we obtain the same intrinsic surface brightness sensitivity, accounting for cosmological dimming. We detect extended Lyα emission around 6 out of 18 high-z LAEs in the MUSE eXtremely Deep Field (MXDF), more than doubling the number of known such objects at z≥6. We obtain an only slightly higher individual LAH detection fraction of 40% among the lower redshift comparison sample. Yet the typical exponential scale lengths at z≥6 are three times smaller than those at z∼3. Stacking the LAEs with undetected haloes gives again drastically different results for the two samples, with a highly significant halo detection at z∼ 3 but no trace of extended Lyα emission at z≥6. We also find the Lyα spectral line widths of the high-z sample to be ∼2.5 smaller in comparison to the lower redshift objects. We discuss the potential mechanisms driving such strong changes. In a reionisation-driven scenario the higher neutral fraction in the intergalactic and circumgalactic media might lead to substantial scattering losses of escaping Lyα radiation, leaving detectable only emission from the vicinity of the star-forming regions. In an alternative scenario the LAH properties might be linked more closely to the evolution of their host galaxies than previously thought.
ER -