Dark Energy Survey: DESI-Independent Angular BAO Measurement

TL;DR

This work constructs a DESI-independent angular BAO likelihood by excluding the DESI-overlapping sky in the DES Y6 data and validating it with COLA mocks, yielding robust $w( heta)$-based BAO measurements. Using the DES BAO-noDESI sample with SN, Planck CMB, and DESI BAO (DR1/DR2), the authors quantify the preference for the time-varying dark energy model $w_0w_a{ m CDM}$ over $oldsymbol{ m Lambda{CDM}}$, finding a modest but notable increase in significance (up to about $4.1}{oldsymbol{ sigma}}$ in some data combinations). Adoption of the DES SN-Dovekie sample shifts constraints toward $oldsymbol{ m Lambda{CDM}}$, reducing tension by roughly $0.8$–$0.9}{oldsymbol{ sigma}}$ but not eliminating it. The study also releases the BAOfit_wtheta code and the DESI-independent DES BAO likelihoods, enabling independent cross-checks and future joint analyses with DESI DR3/DR4.

Abstract

We present a measurement of the angular Baryon Acoustic Oscillation (BAO) scale from the completed Dark Energy Survey (DES) dataset excluding the area of overlap with the Dark Energy Spectroscopic Instrument (DESI). We follow the same methodology and validation process as in the DES Y6 BAO analysis. We interpret the impact of this measurement in the context of the statistical preference for $w_0w_a$CDM over $Λ$CDM when combined with DES Y5 Type Ia supernovae (SN), Planck Cosmic Microwave Background (CMB) and DESI BAO. Based on our previous work, using the full Y6 DES BAO sample, in combination with SN, CMB and DESI DR1 BAO, added 0.3$σ$ in this preference (from 3.7$σ$ to 4.0$σ$), but this ignored possible correlations between datasets. Using our new DESI-independent DES BAO likelihood instead, we find a smaller increase in the statistical preference for $w_0w_a$CDM, from 3.7$σ$ to 3.8$σ$ when using DESI DR1 BAO, and from 4.0$σ$ to 4.1$σ$ when updating to the more recent DESI DR2 BAO. These significances reduce to 3.1$σ$ when using the new calibrated DES SN-Dovekie. Alongside this work, we publicly release BAOfit_wtheta, the BAO fitting code for the angular correlation function used in the DES Y6 BAO analysis.

Figures (6)

• Figure 1: Splits of the DES Y6 BAO angular mask into the overlapping area with DESI (yellow, DES DESI region) and the non-overlapping one (purple, DES no-DESI region). Left: split performed using a DESI mask created from the DESI DR1 tiles. Right: split performed with a cut at $\mathrm{Dec} = -23.5$ deg.
• Figure 2: Angular correlation functions, or $w(\theta)$, for the full sample and the two no-DESI samples ( DR1tiles_noDESI and Deccut_noDESI). The error bars come from the CosmoLike covariance matrices, described in \ref{['sec:cov']}, computed for each of the samples. Points are slightly shifted horizontally to avoid overlap.
• Figure 3: $\Delta\chi^2$ profile for the full sample and the two no-DESI samples ( DR1tiles_noDESI and Deccut_noDESI). The three curves have been stretched to account for the systematic uncertainty given by \ref{['eq:bao_sys']}. In colored dashed lines, we show the $\Delta\chi^2$ obtained when trying to fit the data with a template without BAO. The 1, 2, 3, 4 and 5$\sigma$ limits are shown as horizontal black dashed black lines. We see that all the cases have a significance for the detection of the BAO peak within 3 and 4$\sigma$, being the full sample case the highest one, as expected.
• Figure 4: Results of the BAO fits for the individual redshift bins for the full sample and the two no-DESI samples ( DR1tiles_noDESI and Deccut_noDESI). Bin 1 has a non-detection and, therefore, it is omitted from the plot.
• Figure 5: Ratio between the $D_M(z)/r_d$ measured using the BAO feature at different redshifts and the prediction from the cosmological parameters determined by Planck-2018, assuming $\Lambda{\rm CDM}$ (black line). We include all the measurements from the DESI DR2 BAO analysis in different colors, the fiducial DES Y6 BAO measurement as a golden star and the DES no-DESI BAO measurement as a brown star (from the DR1tiles_noDESI sample). We shifted the redshift of the latter so that it does not overlap with the measurement on the full sample, but they share the same effective redshift.