TY - JOUR
T1 - The Lyman-α Forest from LBGs
T2 - First 3D Correlation Measurement with DESI and Prospects for Cosmology
AU - DESI Collaboration
AU - Herrera-Alcantar, Hiram K.
AU - Armengaud, Eric
AU - Yèche, Christophe
AU - Gordon, Calum
AU - Casas, Laura
AU - Font-Ribera, Andreu
AU - Magneville, Christophe
AU - Ravoux, Corentin
AU - Aguilar, J.
AU - Ahlen, S.
AU - Anand, A.
AU - Brooks, D.
AU - Chaussidon, E.
AU - Claybaugh, T.
AU - Cuceu, A.
AU - Dawson, K. S.
AU - Macorra, A. de la
AU - Doel, P.
AU - Ferraro, S.
AU - Forero-Romero, J. E.
AU - Gaztañaga, E.
AU - Gontcho, S. Gontcho A
AU - Gonzalez-Morales, A. X.
AU - Gutierrez, G.
AU - Guy, J.
AU - Hahn, C.
AU - Kirkby, D.
AU - Kremin, A.
AU - Lahav, O.
AU - Lambert, A.
AU - Landriau, M.
AU - Guillou, L. Le
AU - Manera, M.
AU - Martini, P.
AU - Meisner, A.
AU - Miquel, R.
AU - Muñoz-Gutiérrez, A.
AU - Nadathur, S.
AU - Palanque-Delabrouille, N.
AU - Percival, W. J.
AU - Prada, F.
AU - Pérez-Ràfols, I.
AU - Rossi, G.
AU - Sanchez, E.
AU - Schlegel, D.
AU - Schubnell, M.
AU - Silber, J.
AU - Sprayberry, D.
AU - Tarlé, G.
AU - Weaver, B. A.
PY - 2025/12/22
Y1 - 2025/12/22
N2 - The Lyman-α (Lyα) 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 Lyα forest studies. We analyze 4,151 Lyα 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 Lyα forest auto-correlation function derived exclusively from LBG spectra, probing comoving separations up to 48 h-1 Mpc at an effective redshift of zeff = 2.70. The measured LBG Lyα forest auto-correlation is consistent with that derived from DESI DR2 quasar Lyα forest spectra at a comparable redshift, validating the use of LBGs as reliable background sources for Lyα forest analyses. In addition, we measure the cross-correlation between the LBG Lyα 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 deg2, targeting 1,000 LBGs per square degree at signal-to-noise levels comparable to our sample, could enable LBG-based Lyα forest baryon acoustic oscillation (BAO) measurements with expected uncertainties of σαISO = 0.4% (isotropic) and σαAP = 1.3% (Alcock-Paczynski). This performance is further enhanced when combining the BAO analysis with a Lyα forest Full Shape (FS) approach, yielding a predicted uncertainty of σαISOFS = 0.6%. These results open a new avenue for precision cosmology at high redshift using the Lyα forest in dense LBG samples.
AB - The Lyman-α (Lyα) 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 Lyα forest studies. We analyze 4,151 Lyα 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 Lyα forest auto-correlation function derived exclusively from LBG spectra, probing comoving separations up to 48 h-1 Mpc at an effective redshift of zeff = 2.70. The measured LBG Lyα forest auto-correlation is consistent with that derived from DESI DR2 quasar Lyα forest spectra at a comparable redshift, validating the use of LBGs as reliable background sources for Lyα forest analyses. In addition, we measure the cross-correlation between the LBG Lyα 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 deg2, targeting 1,000 LBGs per square degree at signal-to-noise levels comparable to our sample, could enable LBG-based Lyα forest baryon acoustic oscillation (BAO) measurements with expected uncertainties of σαISO = 0.4% (isotropic) and σαAP = 1.3% (Alcock-Paczynski). This performance is further enhanced when combining the BAO analysis with a Lyα forest Full Shape (FS) approach, yielding a predicted uncertainty of σαISOFS = 0.6%. These results open a new avenue for precision cosmology at high redshift using the Lyα forest in dense LBG samples.
KW - astro-ph.CO
KW - baryon acoustic oscillations
KW - dark energy experiments
KW - high redshift galaxies
KW - Lyman alpha forest
U2 - 10.1088/1475-7516/2025/12/053
DO - 10.1088/1475-7516/2025/12/053
M3 - Article
SN - 1475-7516
VL - 2025
JO - Journal of Cosmology and Astroparticle Physics
JF - Journal of Cosmology and Astroparticle Physics
IS - 12
M1 - 053
ER -