The Lyman- <i>α</i> forest from LBGs: First 3D correlation measurement with DESI and prospects for cosmology
Abstract The Lyman- α (Ly α ) forest is a key tracer of large-scale structure at redshifts z > 2, traditionally studied using the spectra of luminous but relatively rare quasars. In this work, we explore the viability of using the fainter yet significantly more abundant Lyman Break Galaxies (LBGs) as alternative background sources for Ly α forest studies. We analyze 4,151 Ly α forest skewers extracted from LBG spectra obtained in the DESI pilot surveys conducted in the COSMOS and XMM-LSS fields. From this dataset, we present the first measurement of the Ly α forest auto-correlation function derived exclusively from LBG spectra, probing comoving separations up to 48 h -1 Mpc at an effective redshift of z eff = 2.70. The measured LBG Ly α forest auto-correlation is consistent with that derived from DESI DR2 quasar Ly α forest spectra at a comparable redshift, validating the use of LBGs as reliable background sources for Ly α forest analyses. In addition, we measure the cross-correlation between the LBG Ly α forest and the positions of 13,362 galaxies, demonstrating that this observable serves as a sensitive diagnostic for assessing the precision and accuracy of galaxy redshift estimates, and for identifying and correcting systematic offsets. Finally, using both synthetic LBG spectra and Fisher matrix forecasts, we show that a future wide-area survey covering ∼5,000 deg 2 , targeting 1,000 LBGs per square degree at signal-to-noise levels comparable to our sample, could enable LBG-based Ly α forest baryon acoustic oscillation (BAO) measurements with expected uncertainties of σ α ISO = 0.4% (isotropic) and σ α AP = 1.3% (Alcock-Paczynski). This performance is further enhanced when combining the BAO analysis with a Ly α forest Full Shape (FS) approach, yielding a predicted uncertainty of σ α ISO FS = 0.6%. These results open a new avenue for precision cosmology at high redshift using the Ly α forest in dense LBG samples.
Authors
- D. Kirkby (ORCID: https://orcid.org/0000-0002-8828-5463)
- C. Ravoux (ORCID: https://orcid.org/0000-0002-3500-6635)
- E. Chaussidon (ORCID: https://orcid.org/0000-0001-8996-4874)
- A. Muñoz-Gutiérrez (ORCID: https://orcid.org/0000-0002-3565-0148)
- Alma X. González‐Morales (ORCID: https://orcid.org/0000-0003-4089-6924)
- Graziano Rossi (ORCID: https://orcid.org/0000-0002-5102-5019)
- S. Ferraro (ORCID: https://orcid.org/0000-0003-2658-297X)
- N. Palanque‐Delabrouille (ORCID: https://orcid.org/0000-0003-3188-784X)
- S. Nadathur (ORCID: https://orcid.org/0000-0001-9070-3102)
- H. K. Herrera-Alcantar (ORCID: https://orcid.org/0000-0002-9136-9609)
- Kyle Dawson (ORCID: https://orcid.org/0000-0002-0553-3805)
- Andreu Font-Ribera (ORCID: https://orcid.org/0000-0002-3033-7312)
- E. Armengaud (ORCID: https://orcid.org/0000-0001-7600-5148)
- A Kremin
- Laurent Le Guillou (ORCID: https://orcid.org/0000-0001-7178-8868)
- Christophe Yèche (ORCID: https://orcid.org/0000-0001-5146-8533)
- M. Landriau
- David J. Schlegel (ORCID: https://orcid.org/0000-0002-5042-5088)
- Ignasi Pérez-Ràfols (ORCID: https://orcid.org/0000-0001-6979-0125)
- Axel de la Macorra (ORCID: https://orcid.org/0000-0002-1769-1640)
- B. A. Weaver
- Ruguang Zhou (ORCID: https://orcid.org/0000-0001-8314-3039)
- Marc Manera (ORCID: https://orcid.org/0000-0003-4962-8934)
- Gaston Gutierrez (ORCID: https://orcid.org/0000-0003-0825-0517)
- Adam Lambert (ORCID: https://orcid.org/0000-0001-7035-1787)
- J. Aguilar (ORCID: https://orcid.org/0000-0003-0822-452X)
- Eusebio Sanchez (ORCID: https://orcid.org/0000-0002-9646-8198)
- Laura Casas (ORCID: https://orcid.org/0000-0001-6617-8731)
- G. Tarlé
- Andrei Cuceu (ORCID: https://orcid.org/0000-0002-2169-0595)
- Jeffrey H. Silber (ORCID: https://orcid.org/0000-0001-6415-7910)
- J. E. Forero-Romero (ORCID: https://orcid.org/0000-0002-2890-3725)
- Steven P. Ahlen (ORCID: https://orcid.org/0000-0001-6098-7247)
- Aaron Meisner (ORCID: https://orcid.org/0000-0002-1125-7384)
- W.J Percival
- O. Lahav
- Abhishek Anand (ORCID: https://orcid.org/0000-0001-8263-192X)
- R. Miquel
- Hu Zou (ORCID: https://orcid.org/0000-0002-6684-3997)
- Calum Gordon
- P. Doel (ORCID: https://orcid.org/0000-0002-6397-4457)
- M. Schubnell
- E. Gaztañaga (ORCID: https://orcid.org/0000-0001-9632-0815)
- D Brooks
- Paul Martini (ORCID: https://orcid.org/0000-0002-4279-4182)
- Christophe Magneville
- T. Claybaugh
- J. Guy
- ChangHoon Hahn (ORCID: https://orcid.org/0000-0003-1197-0902)
- Francisco Prada (ORCID: https://orcid.org/0000-0001-7145-8674)
- D. Sprayberry
Institutions
- Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR)
- Institut d'Astrophysique de Paris (FR)
- Laboratoire de Physique Nucléaire et de Hautes Énergies (FR)
- CEA Paris-Saclay (FR)
- Institut de Recherche sur les Lois Fondamentales de l'Univers (FR)
Publication Details
- Journal
- Journal of Cosmology and Astroparticle Physics
- Published
- 2025-12-01
- DOI
- https://doi.org/10.1088/1475-7516/2025/12/053
- Primary Topic
- Radio Astronomy Observations and Technology
- Type
- article
- Field-Weighted Citation Impact
- 0.00