The 21cm-galaxy cross-correlation: Realistic forecast for 21cm signal detection and reionisation constraints
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2025
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| _version_ | 1866912970079993856 |
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| author | Hutter, Anne Heneka, Caroline |
| author_facet | Hutter, Anne Heneka, Caroline |
| contents | 21cm-galaxy cross-correlation will play a key role in confirming the cosmological 21cm signal. We investigate which survey configurations detect the 21cm-LAE cross-correlation signal, and assess its ability to distinguish reionisation scenarios. Our pipeline computes observational uncertainties for the 21cm-galaxy cross-power spectrum, accounting for key survey parameters: the field of view (FoV), limiting luminosity of galaxy surveys $L_α$, redshift uncertainty $σ_z$, and 21cm foreground wedge assumptions. We calculate the signal-to-noise ratio (SNR) of the 21cm-Lyman-$α$ emitter (LAE) cross-power spectrum for two scenarios: one where reionisation is driven by faint or by bright galaxies. We find: (i) SNR increases with larger FoV, fainter $L_α$, and smaller $σ_z$, with the FoV having the strongest impact when $σ_z$ is small. (ii) Under a moderate foreground wedge, photometric-like surveys yield insufficient SNR, and medium-deep ($L_α\gtrsim10^{42.5}$erg s$^{-1}$), wide-area (FoV>20deg$^2$) slitless spectroscopic surveys are needed. (iii) Under an optimistic foreground wedge, detection is possible with deep ($L_α\gtrsim10^{42.3}$erg s$^{-1}$), wide-area (FoV$\gtrsim80$deg$^2$) photometric-like or shallower, small-area (FoV$\simeq2-3$deg$^2$) slitless spectroscopic surveys. (iv) To distinguish the two reionisation scenarios at z=7, moderate foreground wedge scenarios require deep-wide spectroscopic surveys; under an optimistic foreground wedge, shallower, medium-area (FoV$\simeq10$deg$^2$) slitless spectroscopic surveys suffice. (v) Maximising the SNR for 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 - making surveys at z>7 more promising despite lower galaxy number densities. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_15906 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The 21cm-galaxy cross-correlation: Realistic forecast for 21cm signal detection and reionisation constraints Hutter, Anne Heneka, Caroline Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies 21cm-galaxy cross-correlation will play a key role in confirming the cosmological 21cm signal. We investigate which survey configurations detect the 21cm-LAE cross-correlation signal, and assess its ability to distinguish reionisation scenarios. Our pipeline computes observational uncertainties for the 21cm-galaxy cross-power spectrum, accounting for key survey parameters: the field of view (FoV), limiting luminosity of galaxy surveys $L_α$, redshift uncertainty $σ_z$, and 21cm foreground wedge assumptions. We calculate the signal-to-noise ratio (SNR) of the 21cm-Lyman-$α$ emitter (LAE) cross-power spectrum for two scenarios: one where reionisation is driven by faint or by bright galaxies. We find: (i) SNR increases with larger FoV, fainter $L_α$, and smaller $σ_z$, with the FoV having the strongest impact when $σ_z$ is small. (ii) Under a moderate foreground wedge, photometric-like surveys yield insufficient SNR, and medium-deep ($L_α\gtrsim10^{42.5}$erg s$^{-1}$), wide-area (FoV>20deg$^2$) slitless spectroscopic surveys are needed. (iii) Under an optimistic foreground wedge, detection is possible with deep ($L_α\gtrsim10^{42.3}$erg s$^{-1}$), wide-area (FoV$\gtrsim80$deg$^2$) photometric-like or shallower, small-area (FoV$\simeq2-3$deg$^2$) slitless spectroscopic surveys. (iv) To distinguish the two reionisation scenarios at z=7, moderate foreground wedge scenarios require deep-wide spectroscopic surveys; under an optimistic foreground wedge, shallower, medium-area (FoV$\simeq10$deg$^2$) slitless spectroscopic surveys suffice. (v) Maximising the SNR for 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 - making surveys at z>7 more promising despite lower galaxy number densities. |
| title | The 21cm-galaxy cross-correlation: Realistic forecast for 21cm signal detection and reionisation constraints |
| topic | Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.15906 |