The 21cm-galaxy cross-correlation: realistic forecast for 21cm signal detection and reionisation constraints
Context. The 21cm-galaxy cross-correlations are expected to play a key role in the confirmation of the cosmological 21cm signal. Aims. We investigate which survey configurations detect the 21cm-Lyman-<i>α<i/> emitter (LAE) cross-correlation signal and assess its ability to distinguish re...
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| Main Authors: | , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
12 March 2026
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| In: |
Astronomy and astrophysics
Year: 2026, Volume: 707, Pages: 1-17 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202557324 |
| Online Access: | Verlag, kostenfrei, Volltext: https://doi.org/10.1051/0004-6361/202557324 Verlag, kostenfrei, Volltext: https://www.aanda.org/articles/aa/abs/2026/03/aa57324-25/aa57324-25.html 
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| Author Notes: | Anne Hutter and Caroline Heneka |
| Summary: | Context. The 21cm-galaxy cross-correlations are expected to play a key role in the confirmation of the cosmological 21cm signal. Aims. We investigate which survey configurations detect the 21cm-Lyman-<i>α<i/> emitter (LAE) cross-correlation signal and assess its ability to distinguish reionisation scenarios. Methods. Our pipeline computes observational uncertainties for the 21cm-galaxy cross-power spectrum, accounting for key survey parameters. These include field of view (FoV); limiting luminosity of galaxy surveys, <i>L<i/><sub><i>α<i/><sub/>; redshift uncertainty, <i>σ<i/><sub>z<sub/>; and 21cm foreground wedge assumptions. Using this pipeline, we calculated the signal-to-noise ratio (S/N) of the 21cm-LAE cross-power spectrum for two scenarios: one where faint galaxies dominate the ionising photon budget and one where reionisation is driven by bright galaxies.<i>Results.<i/> We find that: (i) S/N increases with a larger FoV, fainter <i>L<i/><sub><i>α<i/><sub/>, and smaller <i>σ<i/><sub>z<sub/>, with the FoV having the strongest impact when <i>σ<i/><sub>z<sub/> is small. (ii) Under a moderate foreground wedge, photometric-like surveys yield an insufficient S/N, and medium-deep (<i>L<i/><sub><i>α<i/><sub/> ≳ 10<sup>42.5<sup/> erg s<sup>−1<sup/>), wide-area (FoV > 20 deg<sup>2<sup/>) slitless spectroscopic or spectroscopic surveys are required. (iii) Under an optimistic foreground wedge, detection is possible with deep (<i>L<i/><sub><i>α<i/><sub/> ≳ 10<sup>42.3<sup/> erg s<sup>−1<sup/>), wide-area (FoV ≳ 80 deg<sup>2<sup/>) photometric-like surveys, or with shallower, small-area (FoV ≃ 2 − 3 deg<sup>2<sup/>) slitless spectroscopic surveys. (iv) To distinguish the two reionisation scenarios at <i>z<i/> = 7, moderate foreground wedge scenarios require deep-wide spectroscopic surveys; under optimistic foreground wedge, assumptions shallower (<i>L<i/><sub><i>α<i/><sub/> ≃ 10<sup>42.8<sup/> erg s<sup>−1<sup/>), medium-area (FoV ≃ 10 deg<sup>2<sup/>) slitless spectroscopic surveys suffice. (v) Maximising the S/N for both detection and model discrimination requires sampling the large-scale peak of the cross-power spectrum, which shifts to larger physical scales as reionisation proceeds, and the less ionisation fronts follow the gas density, thus making surveys at <i>z<i/> > 7, or when the Universe was more neutral (⟨<i>χ<i/><sub>HII<sub/>⟩> 0.5), more promising despite lower galaxy number densities. Conclusions. Our results show that large-area spectroscopic surveys and 21cm foreground cleaning are key for using 21cm-LAE cross-correlations to constrain reionisation beyond the global ionisation state of the intergalactic medium. |
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| Item Description: | Gesehen am 19.05.2026 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202557324 |