The Lyman-$\alpha$ Forest from LBGs: First 3D Correlation Measurement with DESI and Prospects for Cosmology

Abstract

The Lyman-$\alpha$ (Ly$\alpha$) forest is a key tracer of large-scale structure at redshifts z > 2, traditionally studied using spectra of quasars. Here, we explore the viability Lyman Break Galaxies (LBGs) as alternative background sources for Ly$\alpha$ forest studies. We analyze 4,151 Ly$\alpha$ forest skewers extracted from LBG spectra obtained in the DESI pilot surveys in the COSMOS and XMM-LSS fields. We present the first measurement of the Ly$\alpha$ forest auto-correlation function derived exclusively from LBG spectra, probing comoving separations up to 48 $h^{-1}$Mpc at an effective redshift of $z_{\mathrm{eff}}$ = 2.70. The measured signal is consistent with that from DESI DR2 quasar Ly$\alpha$ forest spectra at a comparable redshift, validating LBGs as reliable background sources. We also measure the cross-correlation between the LBG Ly$\alpha$ forest and 13,362 galaxy positions, showing that this observable serves as a sensitive diagnostic for galaxy redshift uncertainties and systematic offsets. Finally, using synthetic LBG spectra and Fisher forecasts, we show that a future wide-area survey over 5000 deg${}^2$, targeting 1000 LBGs per deg${}^2$ at similar signal-to-noise than our dataset, could enable Ly$\alpha$ forest baryon acoustic oscillation (BAO) measurements with 0.4% precision on the isotropic BAO scale and 1.3% on the anisotropic (Alcock-Paczynski) scale. Combining BAO with a Ly$\alpha$ forest full-shape analysis improves the AP constraint to 0.6%. These results open a new path for precision cosmology at high redshift using dense LBG samples.

References in corpus (28)

• DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations
• Baryon Acoustic Oscillations in the Ly-α forest of BOSS quasars
• DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints
• PolyChord: nested sampling for cosmology
• Overview of the Instrumentation for the Dark Energy Spectroscopic Instrument
• The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Baryon acoustic oscillations with Lyman-$\alpha$ forests
• DESI 2024 IV: Baryon Acoustic Oscillations from the Lyman Alpha Forest
• The Spectroscopic Data Processing Pipeline for the Dark Energy Spectroscopic Instrument
• Target Selection and Validation of DESI Quasars
• The Robotic Multi-Object Focal Plane System of the Dark Energy Spectroscopic Instrument (DESI)
• Dark energy and curvature from a future baryonic acoustic oscillation survey using the Lyman-alpha forest
• DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest
• The DESI Survey Validation: Results from Visual Inspection of the Quasar Survey Spectra
• The VLT LBG Redshift Survey - III. The clustering and dynamics of Lyman-break galaxies at z ~ 3
• The SDSS-DR12 large-scale cross-correlation of Damped Lyman Alpha Systems with the Lyman Alpha Forest
• Performance of the Quasar Spectral Templates for the Dark Energy Spectroscopic Instrument
• Simulating the effect of high column density absorbers on the one-dimensional Lyman-alpha forest flux power spectrum
• Constraints on the cosmic expansion rate at redshift 2.3 from the Lyman-$\alpha$ forest
• Second Data Release of the COSMOS Lyman-alpha Mapping and Tomographic Observation: The First 3D Maps of the Detailed Cosmic Web at 2.05<z<2.55
• CoLoRe: fast cosmological realisations over large volumes with multiple tracers
• The extended Baryon Oscillation Spectroscopic Survey: measuring the cross-correlation between the MgII flux transmission field and quasars and galaxies at $z=0.59$
• The Alcock-Paczyński effect from Lyman-$\alpha$ forest correlations: Analysis validation with synthetic data
• The ACCEL${}^2$ project: simulating Lyman-$\alpha$ forest in large-volume hydrodynamical simulations
• ELG Spectroscopic Systematics Analysis of the DESI Data Release 1
• Synthetic spectra for Lyman-$\alpha$ forest analysis in the Dark Energy Spectroscopic Instrument
• Measurement of the small-scale 3D Lyman-$\alpha$ forest power spectrum
• High redshift LBGs from deep broadband imaging for future spectroscopic surveys
• Effective Opacity of the Intergalactic Medium from Galaxy Spectra Analysis