Probing the limits of cosmological information from the Lyman-$\alpha$ forest 2-point correlation functions

Wynne Turner; Andrei Cuceu; Paul Martini; J. Aguilar; S. Ahlen; A. Anand; D. Bianchi; D. Brooks; L. Casas; T. Claybaugh; A. de la Macorra; B. Dey; P. Doel; S. Ferraro; A. Font-Ribera; J. E. Forero-Romero; E. Gaztañaga; S. Gontcho A Gontcho; G. Gutierrez; H. K. Herrera-Alcantar; K. Honscheid; M. Ishak; R. Joyce; R. Kehoe; D. Kirkby; A. Kremin; O. Lahav; M. Landriau; L. Le Guillou; M. Manera; R. Miquel; A. Muñoz-Gutiérrez; S. Nadathur; G. Niz; N. Palanque-Delabrouille; W. J. Percival; C. Poppett; F. Prada; A. J. Ross; G. Rossi; E. Sanchez; D. Schlegel; M. Schubnell; H. Seo; J. Silber; D. Sprayberry; G. Tarlé; M. Walther; B. A. Weaver; R. Zhou; H. Zou

arXiv · 2509.14322

Probing the limits of cosmological information from the Lyman-$\alpha$ forest 2-point correlation functions

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Abstract

The standard cosmological analysis with the Ly$\alpha$ forest relies on a continuum fitting procedure that suppresses information on large scales and distorts the three-dimensional correlation function on all scales. In this work, we present the first cosmological forecasts without continuum fitting distortion in the Ly$\alpha$ forest, focusing on the recovery of large-scale information. Using idealized synthetic data, we compare the constraining power of the full shape of the Ly$\alpha$ forest auto-correlation and its cross-correlation with quasars using the baseline continuum fitting analysis versus the true continuum. We find that knowledge of the true continuum enables a $\sim10\%$ reduction in uncertainties on the Alcock-Paczy\'nski (AP) parameter and the matter density, $\Omega_\mathrm{m}$. We also explore the impact of large-scale information by extending the analysis up to separations of $240\,h^{-1}\mathrm{Mpc}$ along and across the line of sight. The combination of these analysis choices can recover significant large-scale information, yielding up to a $\sim15\%$ improvement in AP constraints. This improvement is analogous to extending the Ly$\alpha$ forest survey area by $\sim40\%$.

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Wynne Turner, Andrei Cuceu, Paul Martini, J. Aguilar, S. Ahlen, A. Anand, D. Bianchi, D. Brooks, L. Casas, T. Claybaugh, A. de la Macorra, B. Dey, P. Doel, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, H. K. Herrera-Alcantar, K. Honscheid, M. Ishak, R. Joyce, R. Kehoe, D. Kirkby, A. Kremin, O. Lahav, M. Landriau, L. Le Guillou, M. Manera, R. Miquel, A. Muñoz-Gutiérrez, S. Nadathur, G. Niz, N. Palanque-Delabrouille, W. J. Percival, C. Poppett, F. Prada, A. J. Ross, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, H. Seo, J. Silber, D. Sprayberry, G. Tarlé, M. Walther, B. A. Weaver, R. Zhou, H. Zou. 2025-09-17. Probing the limits of cosmological information from the Lyman-$\alpha$ forest 2-point correlation functions. https://arxiv.org/abs/2509.14322

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