DESI DR2 quasar sample yields bias b_Q(z=2.48)=3.61 that evolves as b(z)=0.230[(1+z)^2-6.565]+2.394, consistent with constant ~10^12 M_sun halo mass and weak luminosity dependence at fixed redshift.
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The Optical Corrector for the Dark Energy Spectroscopic Instrument
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abstract
The Dark Energy Spectroscopic Instrument (DESI) is currently measuring the spectra of 40\,million galaxies and quasars, the largest such survey ever made to probe the nature of cosmological dark energy. The 4-meter Mayall telescope at Kitt Peak National Observatory has been adapted for DESI, including the construction of a 3.2-degree diameter prime focus corrector that focuses astronomical light onto a 0.8-meter diameter focal surface with excellent image quality over the DESI bandpass of 360-980nm. The wide-field corrector includes six lenses, as large as 1.1-meters in diameter and as heavy as 237\,kilograms, including two counter-rotating wedged lenses that correct for atmospheric dispersion over Zenith angles from 0 to 60 degrees. The lenses, cells, and barrel assembly all meet precise alignment tolerances on the order of tens of microns. The barrel alignment is maintained throughout a range of observing angles and temperature excursions in the Mayall dome by use of a hexapod, which is itself supported by a new cage, ring, and truss structure. In this paper we describe the design, fabrication, and performance of the new corrector and associated structure, focusing on how they meet DESI requirements. In particular we describe the prescription and specifications of the lenses, design choices and error budgeting of the barrel assembly, stray light mitigations, and integration and test at the Mayall telescope. We conclude with some validation highlights that demonstrate the successful corrector on-sky performance, and list some lessons learned during the multi-year fabrication phase.
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representative citing papers
DESI DR2 and ACT DR6 data yield 17σ LRG-velocity, 8.3σ ELG-velocity, and 6.8σ QSO-velocity detections plus a 3.1σ velocity-velocity signal, producing f_NL^loc = 15.9_{-34.4}^{+34.6} from the velocity field.
DESI DR1 Lyman-alpha data yields Δ²★=0.379±0.032 and n★=-2.309±0.019 at k★=0.009 km⁻¹s and z=3, sharpening N_eff, α_s, and β_s constraints by factors of 1.18-1.90 when combined with other probes.
DESI DR2 BAO data exhibits 2.3 sigma tension with CMB in Lambda-CDM but prefers evolving dark energy (w0 > -1, wa < 0) at 3.1 sigma with CMB and 2.8-4.2 sigma when including supernovae.
A catalog-level Alcock-Paczynski wavelength-shift blinding scheme for the Lyman-alpha forest robustly hides the expansion history and correctly shifts the BAO peak on DESI DR1 data and mocks.
Combining FAST and DESI data for 2.5 million galaxies shows cosmic atomic hydrogen density declined by only a factor of 1.35 over 4.5 Gyr, far less than the 2.46-fold decline in star formation.
DESI LAE clustering measurements give a linear bias of 2.31-2.62 with constraints on radiative transfer effects and halo occupation from correlation functions and power spectra.
Reports first config-space f_NL measurement from DESI DR1 LRG/QSO 2pcf, yielding joint f_NL = -3^{+12}_{-12} at 68% CL using simulation-based modeling and imaging systematics mitigation.
High-significance kSZ measurements around LRGs show gas is redistributed beyond gravitational collapse and imply more efficient feedback in group-scale halos than in standard hydrodynamical models.
A heuristic power-spectrum rescaling applied to DESI DR1 BAO data plus CMB acoustic scale anchor yields H0 values of 69.2 to 70.3 km/s/Mpc at sub-2% precision across three independent late-time datasets.
Using idealized synthetic data, knowing the true continuum in Lyα forest auto- and cross-correlations reduces uncertainties on the AP parameter and Ω_m by ~10%, with extension to 240 h^{-1}Mpc scales adding up to ~15% further improvement equivalent to a 40% larger survey area.
DESI DR1 full-shape clustering yields Ω_m = 0.2962 ± 0.0095 and σ_8 = 0.842 ± 0.034 in flat ΛCDM, tightening to H_0 = 68.40 ± 0.27 km/s/Mpc with CMB and DESY3, while favoring w_0 > -1, w_a < 0 and limiting neutrino mass sum to < 0.071 eV.
DESI DR1 full-shape galaxy clustering constrains Omega_m = 0.296 ± 0.010, H0 = 68.63 ± 0.79 km/s/Mpc, and sigma_8 = 0.841 ± 0.034, consistent with LambdaCDM and Planck.
DESI measures BAO from the Lyα forest at z_eff=2.33, reporting H(z) = (239.2 ± 4.8) (147.09 Mpc/rd) km/s/Mpc and DM(z) = (5.84 ± 0.14) (rd/147.09 Mpc) Gpc.
Cross-correlating LRG and QSO samples in DESI DR1 yields f_NL^loc = 2.1 with 68% uncertainties of +8.8 and -8.3, an incremental improvement over auto-correlations alone.
Cross-correlation of DESI DR1 quasars with Planck PR4 CMB lensing constrains local f_NL to 2^{+28}_{-34} (p=1.6) or 6^{+20}_{-24} (p=1.0), tightening previous limits by 35%.
Combining LRG and ELG tracers with bias weighting improves BAO constraints by 11% on alpha_iso and 7% on alpha_AP in DESI DR1 data for the 0.8<z<1.1 bin.
DESI DR2 BAO and full-shape data plus CMB yield ∑m_ν < 0.0642 eV (95% CL) under ΛCDM, in 3σ tension with oscillation lower limits, relaxed to <0.163 eV in w0waCDM.
DESI DR1 bispectrum plus DR2 BAO data raise σ8 and S8 by ~1.1-1.2σ while tightening uncertainties, shift DESI-only w0waCDM toward ΛCDM, produce a 2.8σ deviation from ΛCDM when combined with CMB, and yield a neutrino mass sum posterior of 0.26±0.17 eV.
Unsupervised UMAP plus Friends-of-Friends clustering on 58 million DESI DR2 spectra identifies 1.1 million outlier candidates where visual checks show 67 percent have reduction artifacts missed by the standard pipeline.
Property-dependent systematic weights derived separately on ELG subsamples, with separate DES footprint treatment, mitigate spurious clustering in ~10% of subsamples but are not optimal for the full sample.
DESI DR1 constrains the modified gravity parameter to log10 |f_R0| < -4.59 at 95% CL, implying no detectable fifth force on scales below about 18 Mpc.
Extended analysis of DESI DR2 data confirms robust evidence for dynamical dark energy with phantom crossing preference, stable under parametric and non-parametric modeling.
DESI DR2 delivers 0.65% precision BAO measurements from the LyA forest at z_eff=2.33, with D_H/r_d = 8.632 ± 0.098 ± 0.026 and D_M/r_d = 38.99 ± 0.52 ± 0.12.
citing papers explorer
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Clustering of high-redshift quasars with DESI DR2
DESI DR2 quasar sample yields bias b_Q(z=2.48)=3.61 that evolves as b(z)=0.230[(1+z)^2-6.565]+2.394, consistent with constant ~10^12 M_sun halo mass and weak luminosity dependence at fixed redshift.
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Measurement of the galaxy-velocity power spectrum of DESI tracers with the kinematic Sunyaev-Zeldovich effect using DESI DR2 and ACT DR6
DESI DR2 and ACT DR6 data yield 17σ LRG-velocity, 8.3σ ELG-velocity, and 6.8σ QSO-velocity detections plus a 3.1σ velocity-velocity signal, producing f_NL^loc = 15.9_{-34.4}^{+34.6} from the velocity field.
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Cosmological analysis of the DESI DR1 Lyman alpha 1D power spectrum
DESI DR1 Lyman-alpha data yields Δ²★=0.379±0.032 and n★=-2.309±0.019 at k★=0.009 km⁻¹s and z=3, sharpening N_eff, α_s, and β_s constraints by factors of 1.18-1.90 when combined with other probes.
-
DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints
DESI DR2 BAO data exhibits 2.3 sigma tension with CMB in Lambda-CDM but prefers evolving dark energy (w0 > -1, wa < 0) at 3.1 sigma with CMB and 2.8-4.2 sigma when including supernovae.
-
Alcock-Paczynski Blinding Scheme for the Ly-$\alpha$ Forest Analysis
A catalog-level Alcock-Paczynski wavelength-shift blinding scheme for the Lyman-alpha forest robustly hides the expansion history and correctly shifts the BAO peak on DESI DR1 data and mocks.
-
Weak Evolution of Cosmic Atomic Hydrogen over the Past 4.5 Billion Years
Combining FAST and DESI data for 2.5 million galaxies shows cosmic atomic hydrogen density declined by only a factor of 1.35 over 4.5 Gyr, far less than the 2.46-fold decline in star formation.
-
The 3D clustering of Lyman Alpha Emitters measured with DESI
DESI LAE clustering measurements give a linear bias of 2.31-2.62 with constraints on radiative transfer effects and halo occupation from correlation functions and power spectra.
-
Measuring local primordial non-Gaussianity from the clustering of DESI DR1 LRGs and QSOs
Reports first config-space f_NL measurement from DESI DR1 LRG/QSO 2pcf, yielding joint f_NL = -3^{+12}_{-12} at 68% CL using simulation-based modeling and imaging systematics mitigation.
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Precision Kinematic Sunyaev--Zel'dovich Measurements Across Halo Mass and Redshift with DESI DR2 and ACT DR6: Part I. Luminous Red Galaxies
High-significance kSZ measurements around LRGs show gas is redistributed beyond gravitational collapse and imply more efficient feedback in group-scale halos than in standard hydrodynamical models.
-
$H_0$ Without the Sound Horizon (or Supernovae): A 2% Measurement in DESI DR1
A heuristic power-spectrum rescaling applied to DESI DR1 BAO data plus CMB acoustic scale anchor yields H0 values of 69.2 to 70.3 km/s/Mpc at sub-2% precision across three independent late-time datasets.
-
Probing the limits of cosmological information from the Lyman-$\alpha$ forest 2-point correlation functions
Using idealized synthetic data, knowing the true continuum in Lyα forest auto- and cross-correlations reduces uncertainties on the AP parameter and Ω_m by ~10%, with extension to 240 h^{-1}Mpc scales adding up to ~15% further improvement equivalent to a 40% larger survey area.
-
DESI 2024 VII: Cosmological Constraints from the Full-Shape Modeling of Clustering Measurements
DESI DR1 full-shape clustering yields Ω_m = 0.2962 ± 0.0095 and σ_8 = 0.842 ± 0.034 in flat ΛCDM, tightening to H_0 = 68.40 ± 0.27 km/s/Mpc with CMB and DESY3, while favoring w_0 > -1, w_a < 0 and limiting neutrino mass sum to < 0.071 eV.
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DESI 2024 V: Full-Shape Galaxy Clustering from Galaxies and Quasars
DESI DR1 full-shape galaxy clustering constrains Omega_m = 0.296 ± 0.010, H0 = 68.63 ± 0.79 km/s/Mpc, and sigma_8 = 0.841 ± 0.034, consistent with LambdaCDM and Planck.
-
DESI 2024 IV: Baryon Acoustic Oscillations from the Lyman Alpha Forest
DESI measures BAO from the Lyα forest at z_eff=2.33, reporting H(z) = (239.2 ± 4.8) (147.09 Mpc/rd) km/s/Mpc and DM(z) = (5.84 ± 0.14) (rd/147.09 Mpc) Gpc.
-
Local primordial non-Gaussianity using cross-correlations of DESI tracers
Cross-correlating LRG and QSO samples in DESI DR1 yields f_NL^loc = 2.1 with 68% uncertainties of +8.8 and -8.3, an incremental improvement over auto-correlations alone.
-
Constraining primordial non-Gaussianity from DESI DR1 quasars and Planck PR4 CMB Lensing
Cross-correlation of DESI DR1 quasars with Planck PR4 CMB lensing constrains local f_NL to 2^{+28}_{-34} (p=1.6) or 6^{+20}_{-24} (p=1.0), tightening previous limits by 35%.
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Combined tracer analysis for DESI 2024 BAO
Combining LRG and ELG tracers with bias weighting improves BAO constraints by 11% on alpha_iso and 7% on alpha_AP in DESI DR1 data for the 0.8<z<1.1 bin.
-
Constraints on Neutrino Physics from DESI DR2 BAO and DR1 Full Shape
DESI DR2 BAO and full-shape data plus CMB yield ∑m_ν < 0.0642 eV (95% CL) under ΛCDM, in 3σ tension with oscillation lower limits, relaxed to <0.163 eV in w0waCDM.
-
Cosmological constraints from the DESI DR1 Bispectrum Full-Shape and DR2 BAO
DESI DR1 bispectrum plus DR2 BAO data raise σ8 and S8 by ~1.1-1.2σ while tightening uncertainties, shift DESI-only w0waCDM toward ΛCDM, produce a 2.8σ deviation from ΛCDM when combined with CMB, and yield a neutrino mass sum posterior of 0.26±0.17 eV.
-
Quality Assessment of Spectroscopic Data Reduction Pipelines Using Artificial Intelligence: Scrutinizing Data Release 2 from the DESI Survey
Unsupervised UMAP plus Friends-of-Friends clustering on 58 million DESI DR2 spectra identifies 1.1 million outlier candidates where visual checks show 67 percent have reduction artifacts missed by the standard pipeline.
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DESI Data Release 2 ELGs: Property-dependent subsamples, imaging systematics, and clustering
Property-dependent systematic weights derived separately on ELG subsamples, with separate DES footprint treatment, mitigate spurious clustering in ~10% of subsamples but are not optimal for the full sample.
-
Testing Scale-Dependent Modified Gravity with DESI DR1
DESI DR1 constrains the modified gravity parameter to log10 |f_R0| < -4.59 at 95% CL, implying no detectable fifth force on scales below about 18 Mpc.
-
Extended Dark Energy analysis using DESI DR2 BAO measurements
Extended analysis of DESI DR2 data confirms robust evidence for dynamical dark energy with phantom crossing preference, stable under parametric and non-parametric modeling.
-
DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest
DESI DR2 delivers 0.65% precision BAO measurements from the LyA forest at z_eff=2.33, with D_H/r_d = 8.632 ± 0.098 ± 0.026 and D_M/r_d = 38.99 ± 0.52 ± 0.12.