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

TL;DR

DESI DR1 delivers a blinded Full-Shape analysis of galaxy clustering using over 4.7 million redshifts across six redshift bins, extending BAO results by including redshift-space distortions and equality-scale signals. By employing both Full Modelling and ShapeFit compression within EFT-based perturbation theory, the study achieves a 4.7% precision on fσ8 and constrains ΛCDM parameters with Ω_m=0.296±0.010, H_0=68.63±0.79, and σ_8=0.841±0.034, consistent with Planck. The work integrates advanced mocks (AbacusSummit and EZmocks), a robust covariance framework, and a comprehensive systematic budget, including a novel catalog-level blinding and propagation of systematics to the data vector. The results validate the DESI approach and set the stage for future, significantly tighter constraints with expanded data, reinforcing ΛCDM while enabling rigorous tests of gravity with large-scale structure measurements.

Abstract

We present the measurements and cosmological implications of the galaxy two-point clustering using over 4.7 million unique galaxy and quasar redshifts in the range $0.1<z<2.1$ divided into six redshift bins over a $\sim 7,500$ square degree footprint, from the first year of observations with the Dark Energy Spectroscopic Instrument (DESI Data Release 1). By fitting the full power spectrum, we extend previous DESI DR1 baryon acoustic oscillation (BAO) measurements to include redshift-space distortions and signals from the matter-radiation equality scale. For the first time, this Full-Shape analysis is blinded at the catalogue-level to avoid confirmation bias and the systematic errors are accounted for at the two-point clustering level, which automatically propagates them into any cosmological parameter. When analysing the data in terms of compressed model-agnostic variables, we obtain a combined precision of 4.7\% on the amplitude of the redshift space distortion signal reaching similar precision with just one year of DESI data than with 20 years of observation from previous generation surveys. We analyse the data to directly constrain the cosmological parameters within the $Λ$CDM model using perturbation theory and combine this information with the reconstructed DESI DR1 galaxy BAO. Using a Big Bang Nucleosynthesis Gaussian prior on the baryon density parameter, and a Gaussian prior on the spectral index, we constrain the matter density is $Ω_m=0.296\pm 0.010 $ and the Hubble constant $H_0=(68.63 \pm 0.79)[{\rm km\, s^{-1}Mpc^{-1}}]$. Additionally, we measure the amplitude of clustering $σ_8=0.841 \pm 0.034$. The DESI DR1 results are in agreement with the $Λ$CDM model based on general relativity with parameters consistent with those from Planck. The cosmological interpretation of these results in combination with external datasets are presented in a companion paper.

Figures (26)

• Figure 1: Schematic diagram displaying the different types of analyses we perform or refer to in this paper. The magenta boxes represent the analyses in terms of compressed variables (BAO and ShapeFit), whereas the blue boxes represent the analysis whose variables are the ones of the model assumed (Full Modelling). The Standard compression is not explicitly included as it is considered a particular case of the ShapeFit analysis. Note that both ShapeFit and Full Modelling are considered different types of Full-Shape analyses, in contrast to the BAO analyses, which do not exploit the broadband shape for cosmology inference.
• Figure 2: Constraints on $\Lambda$CDM parameters from the joint fit of the six tracers of DESI DR1 from the Abacus complete mocks (mean of 25 lightcone DESI DR1 realisations). We employ the Full-Modelling approach (velocileptors with the LPT setup) using different choices of priors on counterterms (CT) and stochastic terms (ST), as displayed. For more details on the baseline setup, see \ref{['subsec:methods-baseline']}. The filled(empty) symbols represent the mean(MAP) value. The vertical dashed lines display the expected value given the known cosmology of these mocks. For a given case, the difference between filled and empty markers is caused by the prior volume effect (PVE) and the relative difference between MAP values across different choices of priors is caused by the prior weight effect (PWE). The first five rows correspond to analyses with the covariance corresponding to the complete DESI DR1 volume (across the six redshift bins listed in \ref{['tab:Y1data']}), whereas the last two rows (labelled with $V_{25}$) display the analyses corresponding to the same covariance rescaled to a volume of $25\times$DESI DR1. This allows to illustrate that when the data are highly informative (the volume is large) the projection effects (both PWE and PVE) are largely reduced.
• Figure 3: Toy model example for projection effects for the parameters of the $w_0 w_a$CDM cosmology. The contours display the joint fit of all six DESI DR1 types of tracers on synthetic and noiseless velocileptors-generated power spectrum dataset employing the DESI DR1 data covariance. The orange contours display the results of the Full-Modelling analysis employing baseline choice of priors (as defined in the first item point of \ref{['subsec:methods-projection']} and later described in \ref{['subsec:methods-baseline']}). The empty red contours display the same as the orange contours, but additionally adding DESI DR1 BAO post-reconstruction information. The blue contours display the results where the Jeffreys priors on CT and ST parameters have been implemented (see text for more details), and finally, the empty pink contours display the same as the blue ones but adding the DESI DR1 BAO post-reconstruction information. The black vertical and horizontal dotted lines display the input cosmology of the mock-generated power spectrum. Since the data are noiseless we expect to obtain the same cosmology as the input one. Hence, observed differences between contours and dotted lines reflect the impact of PVE.
• Figure 4: Posteriors obtained when analyzing the mean of 25 Abacus DESI mocks with the DESI DR1 sky geometry covering the six redshift bins of \ref{['tab:Y1data']}. The contours show the results obtained using velocileptors assuming the Full-Modelling analysis, with the Lagrangian PT mode (blue open contours) or Eulerian PT mode (orange solid contours) on a $\Lambda$CDM model with a BBN-like prior. The covariance corresponds to a single DESI DR1 realisation volume.
• Figure 5: Constraints on key parameters from each of the six redshift bins obtained from the mean of 25 Abacus DESI mocks with the DESI DR1 sky geometry. The orange and blue contours display the results obtained using the velocileptors ShapeFit option (with both Eulerian and Lagrangian flavours as indicated). The covariance corresponds to a single DESI DR1 realisation volume. The error bars display the 68% credible intervals. The horizontal dashed grey lines display the expected value for these mocks.