Supernovae Unite: Combining Pantheon+ and DES-SN5YR

Abstract

We present the Hubble diagram and cosmological constraints resulting from the combination of the Pantheon+ and DES-SN5YR supernova (SN) samples, which we refer to as Unite. Unite updates Pantheon+, including methodology improvements that the DES sample enabled, and adds the new SN from the DES survey. This represents the most comprehensive and internally consistent SN Ia dataset available, consisting of 2884 likely type Ia supernovae. This work features consistent SN Ia modelling, sample selection, and bias corrections. We also redetermine host-galaxy stellar masses for over 98% of the sample using a consistent framework. Using Unite alone, for a flat universe with a cosmological constant (Flat-ΛCDM), we find Ω_m = 0.310^+0.012_−0.011. We further present constraints using the Unite sample combined with Cosmic Microwave Background and both DES and DESI Baryon Acoustic Oscillation data. We find strong evidence of tension between CMB measurements and the combined BAO and supernova datasets when fitting a model with constant dark energy equation of state (w), which is alleviated when allowing w to vary with time. For a flat universe with dark energy that has a time-evolving equation of state parametrized by w₀ and w_a we find (Ω_m,w₀,w_a) = (0.305±0.004,−0.861^+0.044_−0.042,−0.60^+0.17_−0.19) with a dark energy Figure of Merit of 315. This corresponds to a ∼30% reduction in the area of the w₀−w_a confidence region relative to previous constraints from the combination of DES Y6, DESI-DR2, and CMB data (arXiv:2605.27221). The Bayesian evidence indicates only weak preference for time evolving dark energy, whereas frequentist analyses yield a preference over Flat-ΛCDM at a significance of 3.3σ (3.1σ) when using the maximum a posteriori probability (maximum likelihood).

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BibTeX RIS

BibTeX

@misc{camilleri2026supernovae,
  title = {{Supernovae Unite: Combining Pantheon+ and DES-SN5YR}},
  author = {R Camilleri and J Lee and T.M Davis and D Rubin and P Shah and D Scolnic and C Lidman and B Popovic and K Grech and M Vincenzi and D Brout and M Acevedo and P Armstrong and B.A Bassett and K Bechtol and R.C Chen and H.T Diehl and J Frieman and L Galbany and A Möller and M Sako and B.O Sánchez and M Sullivan and B.E Tucker},
  howpublished = {HAL},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.05053},
  eprint = {2609.05053},
  archivePrefix = {arXiv},
  url = {https://hal.science/hal-05759144v1},
}

RIS

TY  - UNPB
TI  - Supernovae Unite: Combining Pantheon+ and DES-SN5YR
AU  - R Camilleri
AU  - J Lee
AU  - T.M Davis
AU  - D Rubin
AU  - P Shah
AU  - D Scolnic
AU  - C Lidman
AU  - B Popovic
AU  - K Grech
AU  - M Vincenzi
AU  - D Brout
AU  - M Acevedo
AU  - P Armstrong
AU  - B.A Bassett
AU  - K Bechtol
AU  - R.C Chen
AU  - H.T Diehl
AU  - J Frieman
AU  - L Galbany
AU  - A Möller
AU  - M Sako
AU  - B.O Sánchez
AU  - M Sullivan
AU  - B.E Tucker
PY  - 2026
DA  - 2026/09/09
PB  - HAL
DO  - 10.48550/arxiv.2609.05053
UR  - https://hal.science/hal-05759144v1
AB  - We present the Hubble diagram and cosmological constraints resulting from the combination of the Pantheon+ and DES-SN5YR supernova (SN) samples, which we refer to as Unite. Unite updates Pantheon+, including methodology improvements that the DES sample enabled, and adds the new SN from the DES survey. This represents the most comprehensive and internally consistent SN Ia dataset available, consisting of 2884 likely type Ia supernovae. This work features consistent SN Ia modelling, sample selection, and bias corrections. We also redetermine host-galaxy stellar masses for over 98% of the sample using a consistent framework. Using Unite alone, for a flat universe with a cosmological constant (Flat-ΛCDM), we find Ω_m = 0.310^+0.012_−0.011. We further present constraints using the Unite sample combined with Cosmic Microwave Background and both DES and DESI Baryon Acoustic Oscillation data. We find strong evidence of tension between CMB measurements and the combined BAO and supernova datasets when fitting a model with constant dark energy equation of state (w), which is alleviated when allowing w to vary with time. For a flat universe with dark energy that has a time-evolving equation of state parametrized by w_0 and w_a we find (Ω_m,w_0,w_a) = (0.305±0.004,−0.861^+0.044_−0.042,−0.60^+0.17_−0.19) with a dark energy Figure of Merit of 315. This corresponds to a ∼30% reduction in the area of the w_0−w_a confidence region relative to previous constraints from the combination of DES Y6, DESI-DR2, and CMB data (arXiv:2605.27221). The Bayesian evidence indicates only weak preference for time evolving dark energy, whereas frequentist analyses yield a preference over Flat-ΛCDM at a significance of 3.3σ (3.1σ) when using the maximum a posteriori probability (maximum likelihood).
ER  -

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