Detection of supernova magnitude fluctuations induced by large-scale structure

TL;DR

This work probes the growth of cosmic structure by linking low-z Type Ia SN magnitude fluctuations to the peculiar velocity field and large-scale structure traced by DESI BGS. By formulating and applying the ψ1, ψ2, ψ3 estimators and combining SN–galaxy cross-correlation with galaxy auto-correlations, the authors infer fσ8 ≈ 0.384^{+0.094}_{-0.157}, consistent with Planck ΛCDM predictions. They validate the methodology using Abacus N-body mocks, including SN selection effects, and demonstrate negligible bias from selection. The results establish a novel velocity-based route to measure structure growth and project substantial improvements with upcoming SN surveys, potentially tightening fσ8 by an order of magnitude.

Abstract

The peculiar velocities of supernovae and their host galaxies are correlated with the large-scale structure of the Universe, and can be used to constrain the growth rate of structure and test the cosmological model. In this work, we measure the correlation statistics of the large-scale structure traced by the Dark Energy Spectroscopic Instrument Bright Galaxy Survey Data Release 1 sample, and magnitude fluctuations of type Ia supernova from the Pantheon+ compilation across redshifts z < 0.1. We find a detection of the cross-correlation signal between galaxies and type Ia supernova magnitudes. Fitting the normalised growth rate of structure f sigma_8 to the auto- and cross-correlation function measurements we find f sigma_8 = 0.384 +0.094 -0.157, which is consistent with the Planck LambdaCDM model prediction, and indicates that the supernova magnitude fluctuations are induced by peculiar velocities. Using a large ensemble of N-body simulations, we validate our methodology, calibrate the covariance of the measurements, and demonstrate that our results are insensitive to supernova selection effects. We highlight the potential of this methodology for measuring the growth rate of structure, and forecast that the next generation of type Ia supernova surveys will improve f sigma_8 constraints by a further order of magnitude.

Figures (8)

• Figure 1: Sky map showing the (RA,Dec) distribution of DESI BGS galaxies and Pantheon+ SNe at $z < 0.1$, centred on the North Galactic Pole (NGP) and South Galactic Pole (SGP) regions.
• Figure 2: The normalised redshift probability distributions of DESI BGS galaxies and Pantheon+ SNe at $z < 0.1$. For clarity of presentation, we have applied smoothing to the raw redshift histograms.
• Figure 3: The $\left( \psi_1, \psi_2, \psi_3, \xi_{gg} \right)$ correlation functions in our tests using the Abacus simulations (Sec. \ref{['sec:abacus']}). We show measurements of the mock mean and standard deviation over the realisations as the data points, and best-fit models as the solid lines.
• Figure 4: Mock validation results, using the 675 Abacus mocks without SN selection effects. Top: histogram of the best-fit $f \sigma_8$ and $b \sigma_8$ values from the combined four-statistic fit. Bottom: histogram of the reduced $\chi^2$ values for fits to the individual- and combined four- correlation function measurements.
• Figure 5: The best fit $f \sigma_8$ and error for the Abacus mock (black points, mean and standard deviation across 675 realisations) and the DESI BGS and Pantheon+ data (red points, best fit and error) for a range of minimum fitted separations ($10 - 45 \, h^{-1}$Mpc). The maximum fitted separation is always $100 \, h^{-1}$Mpc.