Dark Energy Spectroscopic Instrument (DESI)

DESI 2024 Results: November 19 Guide

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On November 19, DESI released another set of papers based on year one (Y1) data. The first set of papers, summarized here, was released on April 4 and focused on a particular feature seen in the clustering of tracers called the Baryon Acoustic Oscillation (BAO) standard ruler. These new results provide an extended, “full-shape” analysis of the Y1 data by looking at how galaxies and quasars cluster on different scales, both in the plane of the sky and along the line of sight in redshift space. This page contains a guide to the publications and main results. The papers are available here and on arXiv.

This visualization was made from simulated DESI data and displays the shift in galaxy positions between real and redshift space. Because galaxy distances are inferred from their recessional velocities, galaxy motions result in shifted positions along the line of sight (LOS) in a redshift map. On smaller scales, galaxy positions are “smeared” along the LOS as they rotate within clusters. On larger scales, galaxies fall into dense regions and their positions become “squashed” along the LOS. The latter of these is the type of redshift-space distortion (RSD) that contains information about the growth rate of structure. The simulated box is 500 Mpc/h across, 300 Mpc/h deep, and points are colored by depth. Credit: Claire Lamman and Michael Rashkovetskyi / DESI collaboration

Helpful links

The Y1 results fall into seven main categories. The three highlighted in blue, based on BAO measurements of galaxies and quasars (DESI 2024 III), BAO with the Lyman-alpha forest (DESI 2024 IV), and cosmological inference from these BAO measurements (DESI 2024 VI), were released on April 4. The three highlighted in pink are released on November 19; the construction of galaxy and quasar catalogs for cosmological analyses (DESI 2024 II), full-shape clustering measurements from galaxies and quasars (DESI 2024 V), and cosmological constraints from this full-shape modeling (DESI 2024 VII). This figure shows the publication organization, where each category corresponds to a key collaboration paper with several supporting papers. Summaries for the key papers highlighted in pink, as well as supporting papers, are listed below.

The seven categories in which the DESI 2024 papers are organized. Each topic consists of one key collaboration paper and several supporting papers. The papers of three of these categories (highlighted in pink) are released on November 19. The corresponding supporting and value-added papers are listed below. Image credit: Gustavo Niz
Image credit: Gustavo Niz
Image credit: Gustavo Niz
Image credit: Gustavo Niz

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

November 19 Paper Summaries

Construction of Galaxy and Quasar Catalogs

Creating galaxy and quasar catalogs is essential for DESI’s cosmological analyses. These papers describe how these catalogs were constructed from the forthcoming DESI Data Release 1 (DR1), and include studies of the effects of systematics and incompleteness on the clustering measurements.

DESI 2024 II: Sample Definitions, Characteristics, and Two-Point Clustering Statistics

arXiv: 2411.12020

Summary: This paper presents the details of the DESI ‘large-scale structure (LSS) catalogs’ constructed using data from DESI DR1. It further presents the details of how 2-point clustering measurements and their covariance are calculated using the LSS catalogs.

This plot shows the 2-point clustering measurements in multipoles for the DESI LRG sample, split into three redshift bins. The left-hand panels show the results in configuration space, while the right-hand panels show the results in Fourier space. There is excellent statistical agreement between the mean of 25 mock datasets (black curves) and the DR1 LRG data (colored points).

Characterization of DESI fiber assignment incompleteness effect on 2-point clustering and mitigation methods for DR1 analysis

Corresponding author: Davide Bianchi

arXiv: 2411.12025

Summary: The fiber assignment incompleteness, arising from the limited mobility of the robotic fiber positioner in the DESI focal plane, leads to a scale-dependent suppression of the observed galaxy clustering amplitude. If left uncorrected, this effect can significantly affect the inference of cosmological parameters. In this work, we summarize the methods used to simulate fiber assignment on both mock galaxy catalogs and real data, and we discuss the mitigation strategies we implemented to address this issue. We conclude that we can robustly correct for the fiber incompleteness in DESI DR1, as demonstrated in Figures 11 and 12.

Mitigating Imaging Systematics for DESI 2024 Emission Line Galaxies and Beyond

Corresponding author: Alberto Rosado-Marín

arXiv: 2411.12024

Summary: This paper details the angular systematic treatment used for the DESI DR1 emission-line galaxies (ELGs). Separately, we introduce a new methodology for systematic treatment by combining forward-modeling and regression. Furthermore, we present the impact of imaging systematics on the 2-point clustering measurements of BGS, ELGs, LRGs, and QSOs. We also assess the impact of imaging systematics on the BAO measurement.

Full-Shape Analysis from Galaxies and Quasars

The DESI key papers released in April focused on extracting information from the BAO scale. This new set of papers extends this analysis to extract cosmological information from the full shape of the 2-point clustering statistics, allowing for tighter constraints on cosmological parameters. This is the largest dataset ever used to perform a full-shape analysis, with over 4.7 million galaxy and quasar redshifts spanning 0.1 < z < 2.1. The combined precision on the amplitude of the redshift space distortion (RSD) signal, which probes the growth of structure, is 4.7%. Remarkably, this level of precision from just one year of DESI data is comparable to that of 20 years of data from the Sloan Digital Sky Survey (SDSS).

DESI 2024 V: Full-Shape Galaxy Clustering from Galaxies and Quasars

arXiv: 2411.12021

Summary: For the first time, we have performed a “full-shape” analysis of the galaxy 2-point statistics that extracts information beyond the cosmic ruler, the Baryonic Acoustic Oscillations (BAO), and probes the formation of large-scale structures under gravity. We use a sample of galaxies and quasars collected during the first year of DESI. Our galaxy full-shape analysis is in agreement with BAO for the background evolution and confirms the validity of general relativity as our theory of gravity at cosmological scales.

This figure shows measurements of the growth of structure parameter as a function of redshift, fσ8(z), from DESI DR1 (colored symbols) and the full SDSS program (gray symbols). For comparison, the colored lines represent a range of -0.5 <  μ0 < +0.5, a parameterization of modified gravity models that changes the strength of the gravitational interaction. The case μ0 = 0 corresponds to general relativity, represented with black dashed lines.

Exploring HOD-dependent systematics for the DESI 2024 Full-Shape galaxy clustering analysis

Corresponding author: Nathan Findlay

arXiv: 2411.12023

Summary: We explore how changing the model of how galaxies form affects the cosmology we infer. We find this to have a very minor effect (Figure 6) and include it as an extra uncertainty in our analysis following a new, more generally applicable approach.

Cosmological Inference

This set of papers provides a cosmological interpretation of the full-shape (FS) analysis described above, combined with the previous BAO analysis. These FS+BAO results constrain the density of matter, Ωm, the amplitude of mass fluctuations, σ8, and the Hubble constant, H0, for a flat ΛCDM cosmological model. Additionally, combinations of DESI (FS+BAO) with CMB and Type 1a supernovae continue to favor an evolving dark energy component. The DESI (FS+BAO) data is also used to test for deviations from general relativity, and results show agreement with it.

DESI 2024 VII: Cosmological Constraints from the Full-Shape Modeling of Clustering Measurements

arXiv: 2411.12022

Summary: Analysis of the first year of DESI data, in combination with other probes, shows preference for a cosmological model where the dark energy density evolves in time. This corresponds to the preference of the parameter w0 in the accompanying plot being different from -1, and wa different from 0. This result persists when we go beyond our earlier analysis of baryon acoustic oscillations signature in the clustering of galaxies, quasars, and features in quasar spectra, and extend it to utilize the full clustering signal of these cosmological tracers. When combined with Planck18 data, our data also tightly constrains the sum of the neutrino masses, which has to be below 0.071 eV.

This figure shows constraints on w0 and wa in the dark energy equation of state parameterization w=w0+wa(1-a). The solid contours represent constraints based on the new DESI (BAO+FS) analysis combined with CMB and PantheonPlus, while the dashed contours represent the previous BAO-only DESI data and the same combinations with external datasets.

Modified Gravity Constraints from the Full Shape Modeling of Clustering Measurements from DESI 2024

Corresponding author: Mustapha Ishak

arXiv: 2411.12026

Summary: We have analyzed the data from the first year of DESI allowing for different deviations from general relativity. This analysis combines DESI with CMB data and DES Y3 and is performed at different cosmic times and scales using various methods. We conclude that current data is consistent with general relativity (e.g. μ0 and Σ0 are consistent with 0 in the plot below) and that it still favors an evolving dark energy (wa not 0 and w0 not -1 in the plot below).

BAO Measurements from Galaxies and Quasars

In addition to the papers above, an additional supporting paper for the key paper DESI 2024 III: Baryon Acoustic Oscillations from Galaxies and Quasars, released in April, is now available.

Analytical and EZmock covariance validation for the DESI 2024 results

Corresponding author: Daniel Felipe Forero Sánchez

arXiv: 2411.12027

Summary: In cosmology, estimating uncertainties in large-scale structure analyses is crucial. Two methods are used: analytical covariance, which is fast and flexible but limited in handling complex systematics, and sample covariance, which is more accurate but resource-intensive. For the completed DESI 2024 analyses, analytical covariance is chosen for Baryon Acoustic Oscillations (BAO), while corrected sample covariance is used for Full-Shape analysis due to better accuracy in Fourier space.